From David.Steele@usask.ca Thu May 02 10:30:28 1996
Path: tribune.usask.ca!rover.ucs.ualberta.ca!unixg.ubc.ca!van-bc!news1.io.org!consultronics.on.ca!ki.net!winternet.com!news.neocom.ca!news3.toronto.istar.net!news2.toronto.istar.net!istar.net!newsjunkie.ans.net!newsfeeds.ans.net!howland.reston.ans.net!newsfeed.internetmci.com!in2.uu.net!news.ultranet.com!bigboote.WPI.EDU!bigwpi.WPI.EDU!ralf
From: ralf@chpc.org (Ralph Valentino)
Newsgroups: comp.sys.ibm.pc.hardware.video,comp.sys.ibm.pc.hardware.comm,comp.sys.ibm.pc.hardware.storage,comp.sys.ibm.pc.hardware.cd-rom,comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.hardware.networking,comp.sys.ibm.pc.hardware.chips,comp.sys.ibm.pc.hardware.misc,comp.answers,news.answers
Subject: comp.sys.ibm.pc.hardware.* Frequently Asked Questions (FAQ) Part 1/5
Followup-To: comp.sys.ibm.pc.hardware.misc
Date: 19 Apr 1996 04:47:56 GMT
Organization: Worcester Polytechnic Institute
Lines: 1931
Approved: news-answers-request@MIT.EDU
Distribution: world
Expires: 31 May 1996 00:00:00 GMT
Message-ID: <4l75ts$elh@bigboote.WPI.EDU>
Reply-To: ralf@wpi.edu
NNTP-Posting-Host: bigwpi.wpi.edu
Summary: This is a monthly posting containing a list of Frequently
         Asked Questions (and their answers) pertaining to hardware
         and IBM PC clones.  It should be read by anyone who wishes
         to post to any group in the comp.sys.ibm.pc.hardware.*
         hierarchy.
Originator: ralf@bigwpi.WPI.EDU
Xref: tribune.usask.ca comp.sys.ibm.pc.hardware.video:68166 comp.sys.ibm.pc.hardware.comm:18565 comp.sys.ibm.pc.hardware.storage:68454 comp.sys.ibm.pc.hardware.cd-rom:32304 comp.sys.ibm.pc.hardware.systems:37524 comp.sys.ibm.pc.hardware.networking:12909 comp.sys.ibm.pc.hardware.chips:79481 comp.sys.ibm.pc.hardware.misc:60067 comp.answers:18206 news.answers:69875

Archive-name: pc-hardware-faq/part1
Last-modified: 1996/04/10
Version: 1.19

This FAQ was compiled and written by Willie Lim and Ralph Valentino
with numerous contributions by others.  Acknowledgements are listed at
end of this FAQ.

Copyright notice:

The comp.sys.ibm.pc.hardware.* Frequently Asked Questions is
distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY.  No author or distributor accepts responsibility to anyone
for the consequences of using it or for whether it serves any
particular purpose or works at all, unless he says so in writing.
Refer to the GNU General Public License for full details.

Everyone is granted permission to copy, modify and redistribute this
FAQ, but only under the conditions described in the GNU General Public
License.  Among other things, the copyright notice and this notice
must be preserved on all copies.

Where section authors are noted, the copyright is held by that author.
Where no author is noted, the copyright is held by the FAQ editors
Willie Lim (wlim@lehman.com) and Ralph Valentino (ralf@wpi.wpi.edu).

Changes, additions, comments, suggestions and questions to:
Ralph Valentino ralf@wpi.edu

Table of Contents:

   ==== PART 1 ====

S) 1.0 Introduction
 Q) 1.1  What does this FAQ cover?
 Q) 1.2  Where can I find the latest copy of this FAQ?
 Q) 1.3  Is it ok to (sell/buy/job-offer/advertise) things here?
 Q) 1.4  I have a binary that people are asking for, should I post it here?
 Q) 1.5  +Where should I post?
 Q) 1.6  How come no one answers my questions?
 Q) 1.7  What are the going prices for...?
 Q) 1.8  Who makes/Where can I find [some obscure piece of hardware]?
 Q) 1.9  What is the history of the IBM PC?
S) 2.0 Motherboards
 Q) 2.1  >What are the differences between the 80x86 CPUs?
 Q) 2.2  How do I pick the right processor?
 Q) 2.3  What is the difference between the 386SX/386DX and 486SX/486DX?
 Q) 2.4  What is a ZIF socket?
 Q) 2.5  What is over clocking and should I do it?
 Q) 2.6  Which is faster, a DX-50 or DX2-66
 Q) 2.7  *What is the P24T/Overdrive?
 Q) 2.8  What are the differences between the 80x87 co-processors?
 Q) 2.9  Would a math co-processor speed up my machine?
 Q) 2.10  Can I use a x387 with my 486?
 Q) 2.11  What is the floating point (FDIV) problem with the Pentium?
 Q) 2.12  How can I tell if my Pentium has the FDIV bug?
 Q) 2.13  How do I get a replacement for my buggy Pentium?
 Q) 2.14  Memory terminology, what does it mean?
 Q) 2.15  What happen to my 384k?
 Q) 2.16  How do I tell how big/fast my SIMMs are?
 Q) 2.17  What speed SIMMs do I need?
 Q) 2.18  Will 9 chip and 3 chip SIMMs work together?
 Q) 2.19  What are "single-sided" and "double-sided" 72-pin SIMMs?
 Q) 2.20  What does parity/ECC memory protect the system from?
 Q) 2.21  What happens if I get memory error with or without parity/ECC?
 Q) 2.22  Do I really need parity/ECC?
 Q) 2.23  How do I get a system with parity support?
 Q) 2.24  How do you distinguish between parity and non-parity SIMMs?
 Q) 2.25  Can I use Mac or PS/2 SIMMs in my PC?
 Q) 2.26  What do wait states and burst rates in my BIOS mean?
 Q) 2.27  Cache terminology, what does it mean?
 Q) 2.28  How do I upgrade the size of my cache?
 Q) 2.29  Do I need to fill the "dirty tag" RAM socket on my motherboard?
 Q) 2.30  How fast do my cache RAMs have to be?
 Q) 2.31  Which is the best cache policy, write-through or "write-back?"
 Q) 2.32  What about an n-way set associative cache, isn't it better?
 Q) 2.33  Which is better, ISA/EISA/VLB/PCI/etc?
 Q) 2.34  *What are the (dis)advantages of ISA/VLB/EISA SCSI?
 Q) 2.35  Will an ISA card work in an MCA (PS/2) machine?
 Q) 2.36  What does the "chip set" do?
 Q) 2.37  How do I enter the CMOS configuration menu?
 Q) 2.38  What is bus mastering and how do I know if I have it?
 Q) 2.39  Can I put an ISA cards in EISA or VLB slots?
 Q) 2.40  How should I configure ISA/VLB cards in the EISA config utility?
 Q) 2.41  What is the difference between EISA Standard and Enhanced modes?
 Q) 2.42  Is there any point in putting more than 16M in an ISA machine?
 Q) 2.43  What disadvantages are there to the HiNT EISA chip set?
 Q) 2.44  *Should I change the ISA bus speed?
 Q) 2.45  Why is my PC's clock so inaccurate?
 Q) 2.46  How can I automatically set my PC's clock to the correct time?
 Q) 2.47  What is the battery for and how do I replace it?
 Q) 2.48  Can I use IRQ2 or is it special?
 Q) 2.49  Where do all the IRQ's and DMA Channels go?

   ==== PART 2 ====

S) 3.0 IO controllers/interfaces
 Q) 3.1  *How do IDE/MFM/RLL/ESDI/SCSI interfaces work?
 Q) 3.2  How can I tell if I have MFM/RLL/ESDI/IDE/SCSI?
 Q) 3.3  Do caching controllers really help?
 Q) 3.4  Do IDE controllers use DMA?
 Q) 3.5  Why won't my two IDE drives work together?
 Q) 3.6  Which is better, VLB or ISA IDE?
 Q) 3.7  How do I install a second controller?
 Q) 3.8  >What is EIDE/Fast-ATA/ATA-2/ATAPI what advantages do they have?
 Q) 3.9  Which is better, SCSI or IDE?
 Q) 3.10  Can MFM/RLL/ESDI/IDE and SCSI coexist?
 Q) 3.11  What's the difference between SCSI and SCSI-2? Are they compatible?
 Q) 3.12  How am I suppose to terminate the SCSI bus?
 Q) 3.13  Can I share SCSI devices between computers?
 Q) 3.14  What is Thermal Recalibration?
 Q) 3.15  Can I mount my hard drive sideways/upside down?
 Q) 3.16  How do I swap A: and B:
 Q) 3.17  My floppy drive doesn't work and the light remains on, why?
 Q) 3.18  What is a 16550 and do I need one?
 Q) 3.19  Are there any >4 channel serial port cards?
 Q) 3.20  Should I buy an internal or external modem?
 Q) 3.21  What do all of the modem terms mean?
 Q) 3.22  Why does my fast modem connect at a lower speed?
 Q) 3.23  >What kinds of sound cards are available?
 Q) 3.24  Where can I find EISA/VLB sound and IO cards?
 Q) 3.25  Where can I get DOS drivers for my ethernet card?
 Q) 3.26  How does the keyboard interface work?
 Q) 3.27  Can I fake a keyboard so my computer will boot without it?

   ==== PART 3 ====

S) 4.0 Storage/Retrieval Devices
 Q) 4.1  Why do I lose x Meg on my hard drive?
 Q) 4.2  *Should I get an IDE/floppy/SCSI/parallel port tape drive?
 Q) 4.3  I have two floppies. Can I add a floppy based tape drive?
 Q) 4.4  How fast is a tape drive? Will a dedicated controller improve this?
 Q) 4.5  What is QIC80, QIC40?
 Q) 4.6  How come I can't fit as much stuff on my tape drive as they claim?
 Q) 4.7  Are Colorado/Conner/Archive/... tapes compatible with each other?
 Q) 4.8  How does the drive/software know how long the tape is?
 Q) 4.9  What are all those QICs?
 Q) 4.10  Which QICs are read/write compatible?
 Q) 4.11  What is the CMOS/jumper setting for my hard drive?
S) 5.0 >Video
S) 6.0 Systems
 Q) 6.1  *What should I upgrade first?
 Q) 6.2  Do I need a CPU fan / heat sink
 Q) 6.3  What does the turbo switch do?
 Q) 6.4  How does the front panel LED display measure the system's speed?
 Q) 6.5  Should I turn my computer/monitor off?
 Q) 6.6  Are there any manufacturers/distributers who read the net?

   ==== PART 4 ====

S) 7.0 Diagnostics
 Q) 7.1  What do the POST beeps mean?
 Q) 7.2  What do the POST codes mean?
 Q) 7.3  *I think my cache is bad. What's a good diagnostic?
S) 8.0 Misc
 Q) 8.1  What is the pin out for ...?
 Q) 8.2  *Where are benchmark programs located. What do they mean?
 Q) 8.3  What is Plug and Play?
 Q) 8.4  What is an OEM product?
 Q) 8.5  What size should I set my DOS partitions to be?
 Q) 8.6  How do I get DOS to letter my devices the way I want?
 Q) 8.7  Why won't my system boot from the hard drive?
 Q) 8.8  How do I clean my computer?
 Q) 8.9  *What OS's are available for the PC? Which are free?
 Q) 8.10  *How can I transfer files between my PC and a Unix system?
 Q) 8.11  What tape backup software is available?
 Q) 8.12  Why doesn't my new device work as fast as it should?
 Q) 8.13  My drive lists a MTBF of 300,000 hours. Will it really last 34 years?
 Q) 8.14  How do I find pin 1 on my chip/card/cable/connector?
 Q) 8.15  I've run out of power connectors, what can I do?
 Q) 8.16  What does FCC approval cover and what needs to be approved?
S) 9.0 References
 Q) 9.1  +What other FAQ's are out there?

   ==== PART 5 ====

 Q) 9.2  What do the industry acronyms stand for?
 Q) 9.3  Where can I get the ISA/EISA/VLB/PCI/etc specs?
 Q) 9.4  What books are available for the PC architecture?
 Q) 9.5  What books are available on network programming?
 Q) 9.6  Which companies have ftp sites?
 Q) 9.7  Which companies have WWW sites?
 Q) 9.8  What's the phone number for...
S) 10.0 Acknowledgments

* = incomplete
+ = new or significant changes since last post
> = pointer to one or more other FAQs

S) 1.0 Introduction

Q) 1.1  What does this FAQ cover?

This FAQ covers Frequently Asked Questions from all groups in the
comp.sys.ibm.pc.hardware.* hierarchy.  Software topics are only
included if they are directly related to hardware or hardware
interfacing.

Q) 1.2  Where can I find the latest copy of this FAQ?

If you haven't done so, new users on the net should read
news.announce.newusers. In particular, the following posts are a good
idea:
        A Primer on How to Work With The Usenet Community
        Answers to Frequently Asked Questions About Usenet
        Hints on Writing Style for Usenet
        Introduction to The *.answers Groups

This FAQ is currently posted to news.answers, comp.answers,
comp.sys.ibm.pc.hardware.cd-rom, comp.sys.ibm.pc.hardware.chips,
comp.sys.ibm.pc.hardware.comm, comp.sys.ibm.pc.hardware.misc,
comp.sys.ibm.pc.hardware.networking, comp.sys.ibm.pc.hardware.storage,
comp.sys.ibm.pc.hardware.systems, and comp.sys.ibm.pc.hardware.video.
All posts to news.answers are archived and are available via anonymous
FTP, uucp and e-mail from the following locations:

FTP:
        FTP is a way of copying file between networked computers. If
        you need help in using or getting started with FTP, send
        e-mail to mail-server@rtfm.mit.edu with
                send usenet/news.answers/ftp-list/faq
        as the body of the message.

        location:  rtfm.mit.edu [18.181.0.24]
        directory: /pub/usenet/news.answers/pc-hardware-faq
        filenames: part1 to part5

        location:  ftp.uu.net [137.39.1.9]
        directory: /archive/usenet/news.answers/pc-hardware-faq
        filenames: part1.Z to part5.Z [use uncompress]

        location:  nic.switch.ch [130.59.1.40]
        directory: info_service/Usenet/periodic-postings
        filenames: [Check info_service/Usenet/00index]


UUCP:
        location:  uunet!/archive/usenet/news.answers/pc-hardware-faq/
        filenames: part1.Z to part5.Z

E-mail:
        Send email to mail-server@rtfm.mit.edu containing these lines:
        send usenet/news.answers/pc-hardware-faq/part1
        ...
        send usenet/news.answers/pc-hardware-faq/part5

You can find a dozen or more sites in the US, Europe and Japan that
store the FAQ and archives for this various newsgroups by using the
Internet search programs, Archie or Wais.

Q) 1.3  Is it ok to (sell/buy/job-offer/advertise) things here?

No, none of the above fit within the charter of the
comp.sys.ibm.pc.hardware.* hierarchy, therefore such posts are
considered unacceptable.  For buying/selling things, use groups with
the words 'wanted' or 'forsale', and for job offers, use groups with
the words 'jobs'.  All of these can be found in the misc.* hierarchy.
For commercial advertisements, use only the biz.* hierarchy as per the
guidelines of USENET.  (refer to the news.* groups for more
information).


Q) 1.4  I have a binary that people are asking for, should I post it here?

Never post binaries to technical discussion groups.  If you absolutely
must distribute a binary, you are ENTIRELY sure that it is legal to do
so and it is not currently available via ftp then, in order of
preference:

 1. Privately offer to mail it to the person (if only a few people are
    looking for it).  Don't blindly mail it to anyone making a general
    request until you offer and they accept.
 2. Place it on an anonymous ftp site and, once it is there, post a
    pointer to it.  To find an anonymous ftp site, scan a few groups,
    they always pop up.
 3. Post it to comp.binaries.ibm.pc (moderated), wait for it to be
    approved, and then post a pointer to it.


Q) 1.5  +Where should I post?
[From: grohol@alpha.acast.nova.edu (John M. Grohol)]

PC-Clone Hardware Newsgroup Pointer                   By: John M. Grohol

This Pointer will help you find the information you need and get your
questions answered much quicker than if you were to simply crosspost to
every hardware newsgroup in existence. It is provided as a public service.
Post your article in the most appropriate newsgroup according to its topic.
Please do not post your hardware questions to software newsgroups,
and vice versa. "For Sale" articles are never appropriate to
either the hardware or software newsgroups.

Comments & suggestions are always welcome! 

Question on...                       Post to...
-----------------------------------  ----------------------------------
Networking/networks                  comp.os.netware.* (where * equals:
                                     announce; connectivity; misc;
                                     security)
                                     comp.dcom.lans.* (where * equals:
                                     ethernet; fddi; misc; token-ring)
                                     comp.protocols.tcp-ip.ibmpc
                                     comp.os.os2.networking.misc
                                     comp.os.os2.networking.tcp-ip
                                     comp.os.ms-windows.networking.*
                                     (where * equals: misc; ras; tcp-ip;
                                     windows)
All NFS-based networking             comp.protocols.nfs
All SMB-based networking 
(LANman, LANserver, WNT, Samba, etc) comp.protocols.smb
PC Networking hardware/cards/cables  comp.sys.ibm.pc.hardware.networking
-----------------------------------  ----------------------------------
Home-built personal computers        alt.comp.hardware.pc-homebuilt
Laptops & notebooks (over 3 lbs.)    comp.sys.laptops
Palmtops (under 3 lbs.)              comp.sys.palmtops
-----------------------------------  ----------------------------------
Servers                              comp.dcom.servers
Modems                               comp.dcom.modems
Printers                             comp.periphs.printers
SCSI devices                         comp.periphs.scsi
Other peripherals                    comp.periphs
PCMCIA devices                       alt.periphs.pcmcia
-----------------------------------  ----------------------------------
Acer users & support                 alt.sys.pc-clone.acer
Dell users & support                 alt.sys.pc-clone.dell
Gateway 2000 users & support         alt.sys.pc-clone.gateway2000
Micron users & support               alt.sys.pc-clone.micron
Zenith users & support               comp.sys.zenith
Zeos users & support                 alt.sys.pc-clone.zeos
-----------------------------------  ----------------------------------
Technical topics on PC soundcards    comp.sys.ibm.pc.soundcard.tech
Advocacy for a particular soundcard  comp.sys.ibm.pc.soundcard.advocacy
Using soundcards with games          comp.sys.ibm.pc.soundcard.games
Music & sound using soundcards       comp.sys.ibm.pc.soundcard.music
Soundcards in general                comp.sys.ibm.pc.soundcard.misc
-----------------------------------  ----------------------------------
Discussion of forsale items          misc.forsale.computers.discussion
Mac-specific sale of items           misc.forsale.computers.mac-specific.*
                                     (where * equals: cards.misc;misc; 
                                     cards.video;portables;software;
                                     systems)
Sale of all computer memory,         misc.forsale.computers.*
   modems, monitors, net-hardware,   (where * equals: memory;modems;
   printers, storage devices         monitors;net-hardware;printers;storage)
Sale of other computer items         misc.forsale.computers.other.*
                                     (where * equals: misc;software;systems)
PC-specific sale of items            misc.forsale.computers.pc-specific.*
                                     (where * equals: audio;cards.misc;
                                     cards.video;misc;motherboards;
                                     portables;software;systems)
Commercial sale of hardware          biz.marketplace.computers.*
                                     (where * equals: pc-clone;mac;other;
                                     workstation;discussion)
-----------------------------------  ----------------------------------
Monitors/video cards                 comp.sys.ibm.pc.hardware.video
Modems/fax cards/communication       comp.sys.ibm.pc.hardware.comm
Hard/floppy/tape drives & media      comp.sys.ibm.pc.hardware.storage 
CD-ROM drives & interfaces           comp.sys.ibm.pc.hardware.cd-rom
Computer vendors & specific systems  comp.sys.ibm.pc.hardware.systems
System chips/RAM chips/cache         comp.sys.ibm.pc.hardware.chips
-----------------------------------  ----------------------------------
Other hardware questions             comp.sys.ibm.pc.hardware.misc
-----------------------------------  ----------------------------------
   This Pointer is freely distributable to  any  other mailing list,
   newsgroup,  or  network  service provider  as  long as it remains
   fully intact. Copyright 1994-1996 John M. Grohol. All rights reserved.

   Send comments/questions/suggestions regarding this Pointer to the
   author (replying to this message should work).   Do *not* include
   this entire Pointer in your reply, or it may not be read.


Q) 1.6  How come no one answers my questions?

If you don't give enough information when asking your question, then
people will not be able to answer it.  If you're not willing to take
the time to look up the necessary information, then why should you
expect people to take the time to answer your question?  For instance,
if you're asking a question about SCSI, it is very important to know
what type of SCSI host adapter (controller) you have.  Some other
important things to mention are which device drivers/tsr's you are
loading, what other similar devices you have in your system, and
exactly what in your setup has changed since it last worked.

Q) 1.7  What are the going prices for...?

If you're looking for new equipment, pick up a copy of Computer
Shopper.  This is the "bible" for buying new equipment.  Skim through
it for the best prices and give these distributers a call.  In most
cases, the advertisements must be placed months in advance; the actual
price may be even lower than the advertised price!  Two other things
to note are the warranty, return policy and location of the company
(companies within the same state as you may be required to add extra
sales taxes).

If you're looking for the expected price of used equipment, then scan
the newsgroup misc.forsale.computers.pc-clone for similar items.  This
will give you the best idea as what to expect.  Don't make assumptions
that the price of used equipment will follow the market trends of new
equipment.  For instance, when new memory prices nearly doubled, the
used prices were barely effected.

Q) 1.8  Who makes/Where can I find [some obscure piece of hardware]?
[From: uwvax!astroatc!nicmad!madnix!zaphod (Ron Bean)]

You can ask on the net, but you'll get a better response if you do
some investigating on your own first. Try calling vendors who
advertise similar or related hardware, they often have things that
aren't in the ads. Vendors who specialize in parts rather than
complete systems are a good bet. You can also ask local dealers to
check their wholesale sources.


Q) 1.9  What is the history of the IBM PC?
[From:]

Around 1978 and '79, the market served by IBM's Data Entry Systems
division began to change.  Instead of terminals and minicomputers or
mainframes, customers began demanding autonomous, low cost,
single-user computers with minimal compute power or connectivity, but
compliance to standards like the ASCII alphabet and the BASIC
programming language.  The closest product in IBM's line was the 5110,
a closed, BASIC-in-ROM machine with a tiny built-in character display.
The 5110 was uncompetitive, and IBM started losing bids from key
customers, mostly government agencies.

Data Entry commissioned a consulting firm (Boca Associates?) to design
a stop-gap machine to fill what was perceived within IBM as a
short-lived, specialized niche.  It was intended that the stop-gap
machine would only be offered for a couple of years until it would be
replaced in "The Product Line" by an internal IBM design.  Some IBM
executives believed the single-user desktop system was a fad which
would die out when the shortcomings of such systems became
appreciated.

The motherboard design was based very closely on a single-board
computer described in a 1978 (?) Intel application note.  (Anybody got
an original copy of this collector's item?  Among other things, Intel
argues that 640KB is more memory than single-user applications will
ever need, because of the efficiency of segmented memory
"management"!)  The expansion slot "bus" is based on an Intel bus
called Multibus 1, which Intel introduced in its microprocessor
software development equipment in the mid '70s.  The Monochrome and
Color Graphics Display Adapters are based on application notes for the
Motorola 6845 video controller chip, except that the strangely
interlaced pixel addresses in the CGA appears to have been extremely
short sighted.  The "event driven" keyboard is an original design, but
the concept is from the Xerox Alto and Star graphics workstations.
The keyboard noise and "feel" are intended to emulate those of the IBM
Selectric typewriter.  The Cassette Interface design is original, but
similar in concept to the one on the Radio Shack TRS-80.

Data Entry Division approached Digital Research Inc. to offer its
popular CP/M-86 operating system on the machine, but DRI rebuffed
them.  IBM's second choice was BASIC-in-ROM vendor Microsoft, which
had no OS product at the time but quickly purchased a crude disk
operating system called 86-DOS from Seattle Computer Products to offer
it to IBM.  Its command interpreter was an imitation of Unix' Bourne
Shell, with the special characters changed to avoid infringing AT&T's
rights.

Data Entry Division began bidding this system in various State
procurements, without any plan to offer it to the public.

It became obvious that the Cassette Interface and optional 360KB
Flexible Disk Drive were inadequate.  The Cassette Interface was
dropped, and an optional Fixed Disk Drive offered on a revised model
known as the IBM Personal Computer XT.  (A fixed, or "hard" disk had
been offered on the PC by special order, with a Xebec controller, but
few were sold.)  The disk controller was designed around the Western
Digital 1010 chip, and its design is taken directly from a WD
application note.

The XT succeeded beyond all expectations.  IBM offered the system to
the public after it became clear that no other division was going to
come up with anything timely.  IBM published complete schematics and
ROM listings, encouraging clones.

In 1984, IBM introduced an upwardly compatible model based on the
Intel 80286.  The expansion slot "bus" was extended to 16-bit data
path width the same way Intel had extended Multibus: by adding data
and address bits, a signal for boards to announce their capability to
perform 16-bit transfers, and byte swapping on the motherboard to
support the 8-bit boards.

S) 2.0 Motherboards

Q) 2.1  >What are the differences between the 80x86 CPUs?

This section is posted separately as the "Personal Computer Chiplist"
and archived along side this FAQ.  Refer to section one for
instructions on retrieving this file.

Newsgroups: comp.sys.ibm.pc.hardware.chips,comp.sys.ibm.pc.hardware.systems,
            comp.sys.ibm.pc.hardware.misc,comp.sys.intel
Subject: Personal Computer CHIPLIST 7.0 part * of *
From: offerman@einstein.et.tudelft.nl (Aad Offerman)
Summary: This list contains the various CPU's and NPX's and their features,
         used in the IBM PC, IBM PC/XT, IBM PC/AT, IBM PS/2 and compatbles,
         and the differences between them.
Archive-name: pc-hardware-faq/chiplist

Q) 2.2  How do I pick the right processor?
[From: jabram@ichips.intel.com (Jeff Abramson)]

This is a hard question.  You have tradeoffs between price,
performance, compatibility, upgradebility, and power consumption.
As a desktop unit owner, you probably have less concerns about
power, but as a laptop owner, this is very important.

The frequency of the CPU defines how fast its internal clock runs.
This defines how fast instructions are executed.  In many ways, this
is meaningless, because a RISC machine (MIPS) running at 100MHz may
in reality be slower than a 50Mhz i486 because a RISC system must
execute more instructions to perform the same function (in some
cases).  Even when comparing processors in the same family, this
info can be misleading.  For example, an Intel486-25 is faster than
an AMD386-40, since the 486 has microarchitectural advancements over
the 386.  The same can be said for the Pentium, where a 66Mhz
Pentium is twice as fast as a 66MHz 486.

For compatibility, keep in mind that the Intel parts are the basis
for all of these processors.  Therefore you always run the risk that
an imitator's part may not be compatible.  AMD chips are compatible
because they are copied.  For some of you, these factors may be
important.

As far as upgradability goes, this depends on both your motherboard
and the processor.  If you purchase a 486DX, then you can upgrade to a
DX2 and double your internal clock simply by buying an overdrive chip
if your motherboard has the ZIF socket.  If it doesn't then you can
replace the CPU with a DX2.  Many new 486 motherboards contain
overdrive sockets for the Pentium chip that is pin compatible.

Q) 2.3  What is the difference between the 386SX/386DX and 486SX/486DX?

[From: jabram@ichips.intel.com (Jeff Abramson)]

The Intel386DX contains full 32 bit buses for external data,
internal data, and address.  The Intel386SX contains a smaller 16
bit external data bus, and a smaller 24 bit address bus.

The Intel486DX contains a floating point unit, the Intel486SX does
not.  A common rumor is that the 486SX is simply a DX part that has
a failure in the floating point unit, so it has been disabled and
the part has been produces as an SX.  This was true for early
production parts and samples, but not for the mass produces SX parts
that we see today.  

Q) 2.4  What is a ZIF socket?

[From: jabram@ichips.intel.com (Jeff Abramson)]

ZIF stands for Zero Insertion Force, and describes a socket on your
motherboard that supports an upgrade processor (overdrive
processor).  In general, an overdrive upgrade works in conjunction
with your original processor so you cannot remove the original
processor after upgrade.  NOTE: Some motherboards do not have a ZIF
socket so you must replace the existing processor to upgrade.

Q) 2.5  What is over clocking and should I do it?
[From: jabram@ichips.intel.com (Jeff Abramson)]

Overclocking is a term generally used to describe how you have
increased the clock frequency on your board to run your system at a
higher speed.  For example, if you plug a 25MHz i486 into a board
that is configured to run a 33MHz i486, then you are overclocking
your CPU.  Most boards allow you to configure your clocking via
jumpers, and others require a new clock oscillator.

Although users have had success with overclocking, it is a dangerous
practice for two reasons.  First, the chip has been designed to meet
a certain speed.  Therefore, some circuits do not have the margin to
operate at a higher frequency.  The chips coming from a wafer have
various speed specs (statistical distribution), so you may be lucky
and own a CPU that has the circuit margins you need to overclock.
But you don't know - and if you overclock, you may get data failure.
The data failure may be reproducable - and therefore avoidable, but
most likely not.

Second, you have reliability concerns when overclocking.
Overclocking means faster frequency, which means more current and
power.  This can lead to real failures in your CPU.
Electromigration is one such failure where metal lines in your CPU
will actually break or connect if they get too much current.  This
is irreversable, and most likely not covered under warranty.

So when can you overclock?  Really only if you don't care about
burning out your CPU and you don't care if you get wrong data every
now and then.  If you own a machine and you use it just for games,
then overclocking may be something to try - and you simply upgrade
to a new CPU when you burn out the current one.  Otherwise, it's not
worth the small performance gain.

Q) 2.6  Which is faster, a DX-50 or DX2-66

The two processors are relatively close for overall usage.  The DX-50
has more I/O bandwidth and the DX2-66 has more computational power.

Q) 2.7  *What is the P24T/Overdrive?
Q) 2.8  What are the differences between the 80x87 co-processors?

See reference in: "What are the differences between the 80x86 CPUs?"

Q) 2.9  Would a math co-processor speed up my machine?

[From: jruchak@mtmis1.mis.semi.harris.com (John Anthony Ruchak)]

If you do a lot of number-crunching with CAD/CAM applications,
spreadsheets, and the like, a math co-processor is likely to increase
performance.  If on the other hand, your primary work is word
processing, a math co-processor will have barely any effect at all.
Also, a math co-processor will not provide any benefit if your CPU
already has one built-in (486/586-DX chips).  In addition, a math
co-processor is not likely to improve the over-all performance of
Microsoft Windows, except when you are running the afore-mentioned
number-crunching programs.

Q) 2.10  Can I use a x387 with my 486?

[From: Shaun Burnett (burnesa@cat.com)]

No, they are not pin compatible.  The 486DX and above contain an
on-chip floating point unit. Therefore, a 387 (SX or DX) math
coprocessor is not needed.  All software written for a 387 coprocessor
will run on your 486.
 
If you want a math coprocessor for a 486SX, you need to purchase the
487SX or a 486 Overdrive processor.
 
While we're talking about math coprocessors, I'll make a brief note
about the Weitek.  Some motherboards may have a socket for a Weitek
math coprocessor.  These coprocessors are not compatible with the
Intel 387 math coprocessor and should only be used if your software
requires it.  The Weitek 3167 replaced the Weitek 1167 and is for the
386 while the Weitek 4167 is for a 486.

Q) 2.11  What is the floating point (FDIV) problem with the Pentium?

Under certain circumstances, based on divisor ranges, mantissa bit 13
and beyond can be incorrect during floating point division.  This
problem effects the functions:

    FDIV, FDIVR, FPTAN, FPATAN, FPREM and FPREM1

in single, double and extended precision modes.  Many programs and
operating systems are already incorporating software patches to work
around the problem.  For most users, the accuracy supplied by the
Pentium even without a patch is more than enough.  However, since the
media hype made the problem sound like it would have a serious impact
on everyone, Intel has agreed to replace all faulty Pentiums free of
charge.

Q) 2.12  How can I tell if my Pentium has the FDIV bug?

If you purchased your Pentium in 1994 or earlier, chances are near
100% that it has the problem.  Purchasing it after this date does not
guarantee a bug free CPU.  The problem existed in all speed grades.

The program:

ftp.intel.com:/pub/IAL/pentium/$cpuid.exe    - executable
ftp.intel.com:/pub/IAL/pentium/cpuidf.txt    - instructions

is Intel's official program to identify CPUs with the FDIV bug.  This
program uses the CPU ID register to compare against the list of known
buggy Pentiums rather than attempting to reproduce the bug through
software, so it should be accurate even if the OS has a software FDIV
patch already in place.
 
Q) 2.13  How do I get a replacement for my buggy Pentium?

From the US and Canada, call 1-800-628-8686.  For other countries, see
the file:

 ftp.intel.com:/pub/IAL/pentium/cpusup.txt

Be sure to have your credit card handy.  Intel won't place any charges
on it as long as you return the defective Pentium within 30 days.  If
you don't have a credit card, contact Intel and they will refer you to
a local service center.

Q) 2.14  Memory terminology, what does it mean?
[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

Read/write memory in computers is implemented using Random Access Memory
chips (RAMs).  RAMs are also used to store the displayed image in a video
board, to buffer frames in a network controller or sectors in a disk
controller, etc.  RAMs are sold by their size (in bits), word width (how
many bits can you access in one cycle), and access time (how fast you
can read a location), among other characteristics.


SRAMs and DRAMs
---------------
RAMs can be classified into two types: "static" and "dynamic."

In a static RAM, each bit is represented by the state of a circuit
with two stable states.  Such a "bistable" circuit can be built with four
transistors (for maximum density) or six (for highest speed and lowest
power).  Static RAMs (SRAMs) are available in many configurations.
(Almost) all SRAMs have one pin per address line, and all of them
are able to store data for as long as power is applied, without any
external circuit activity.

In a dynamic RAM (DRAM), each bit is represented by the charge on a
*very* small (30-50 femptofarads) capacitor, which is built into a
single, specialized transistor.  DRAM storage cells take only about
a quarter of the silicon area that SRAM cells take, and silicon
area translates into cost.
The cells in a DRAM are organized into rows and columns.  To access
a bit, you first select its row, and then you select its column.
Unfortunately, the charge leaks off the capacitor over time,
so each cell must be periodically "refreshed" by reading it and
writing it back.  This happens automatically whenever a row is accessed.
After you're finished accessing a row, you have to give the DRAM time
to copy the row of bits back to the cells: the "precharge" time.

Because the row and column addresses are not needed at the same
time, they share the same pins.  This makes the DRAM package smaller
and cheaper, but it makes the problem of distributing the signals
in the memory array difficult, because the timing becomes so
critical.  Signal integrity in the memory array is one of the
things that differentiate a lousy motherboard from a high quality
one.

EDO RAM
-------
Extended Data Out is a minor variation on the control logic in the DRAM
chip that tells the output pin when to turn on.

In a "standard" (Fast Page Mode) DRAM, the output pin turns off as soon
as the Column Address Strobe (CAS) pin goes false.  The problem with
that comes when you try to do a "burst" read cycle wherein Row Address
Strobe (RAS) is held true while CAS toggles up and down real fast.  The
RAM only drives the data half the time and the other half the time is
wasted.  This makes a cache fill cycle take longer than it otherwise
might, because the cache really can't look at the data unless the DRAM
is driving it.  (You can't store data on a PC board trace because of
inductive kick and other effects.  Trust me, you novice board designers
out there.)

In an EDO (Nippon Electric Corp calls it Hyper Page Mode) DRAM, the
output pin keeps driving until RAS and CAS *both* go false.  Your cache
can fill faster because the whole duration (grossly oversimplifying) is
usable as sampling time.

(Why didn't they do it that way to begin with, some of you are asking.
The EDO DRAM can't read and write in the same RAS cycle.  The FPM can.
That used to be important, but it's not a capability that PCs with
caches happen to use.)

With today's (cost-oriented) SRAM and ASIC technology, only synchronous
SRAMs can take much advantage of the extra bandwidth.  That's why you don't
get a big benchmark boost when you switch to EDO but leave your cache
the way it was before.  You have to upgrade both to see the improvement.

Because it's a minor control variation, the chip maker can do most of the
wafer fabrication steps before deciding whether a wafer full of chips will
be FPM or EDO.  Both types can be made on the same process and circuit
design, and tested on the same equipment.  Therefore, once they all tool
up to make it, EDO and FPM will cost about the same.  Right now (July '95)
EDO costs more only because it's still rare.


SIMMs and SIPPs
---------------
Through the 1970s, RAMs were shipped in tubes, and the board makers
soldered them into boards or plugged them into sockets on boards.
This became a problem when end-users started installing their own
RAMs, because the leads ("pins") were too delicate.  Also, the
individual dual in-line package (DIP) sockets took up too much board
area.
In the early 1980s, DRAM manufacturers began offering DRAMs on tiny
circuit boards which snap into special sockets, and by the late '80s
these "single in-line memory modules" (SIMMs) had become the most popular
DRAM packaging.  Board vendors who didn't trust the new SIMM sockets
used modules with pins: single inline pinned packages (SIPPs),
which plug into sockets with more traditional pin receptacles.

PC-compatibles store each byte in main memory with an associated
check bit, or "parity bit."  That's why you add memory in multiples
of nine bits.  The most common SIMMs present nine bits of data at
each cycle (we say they're "nine bits wide") and have thirty contact
pads, or "leads."  (The leads are commonly called "pins" in the trade,
although "pads" is a more appropriate term.  SIMMs don't *have* pins!)

At the high end of the PC market, "36 bit wide" SIMMs with 72 pads
are gaining popularity.  Because of their wide data path, 36-bit SIMMs
give the motherboard designer more configuration options (you can
upgrade in smaller chunks) and allow bandwidth-enhancing tricks
(i.e. interleaving) which were once reserved for larger machines.
Another advantage of 72-lead SIMMs is that four of the leads are used
to tell the motherboard how fast the RAMs are, so it can configure
itself automatically.  (I do not know whether the current crop of
motherboards takes advantage of this feature.)

"3-chip" and "9-chip" SIMMs

In 1988 and '89, when 1 megabit (1Mb) DRAMs were new, manufacturers
had to pack nine RAMs onto a 1 megabyte (1MB) SIMM.  Now (1993) 4Mb DRAMs
are the most cost-effective size.  So a 1MB SIMM can be built with
two 4Mb DRAMs (configured 1M x4) plus a 1Mb (x1) for the check-bit.

VRAMs
-----
In graphics-capable video boards, the displayed image is almost
always stored in DRAMs.  Access to this data must be shared between
the hardware which continuously copies it to the display device (this
process is called "display refresh" or "video refresh") and
the CPU.  Most boards do it by time-sharing ordinary, single-port
DRAMs.  But the faster, more expensive boards use specialized DRAMs
which are equipped with a second data port whose function is tailored
to the display refresh operation.  These "Video DRAMs" (VRAMs) 
have a few extra pins and command a price premium.  They nearly double
the bandwidth available to the CPU or graphics engine.

(As far as I know, the first dual-ported DRAMs were built by Four-
Phase Systems Inc., in 1970, for use in their "IV-70" minicomputers, which
had integrated video.  The major DRAM vendors started offering VRAMs
in about 1983 [Texas Instruments was first], and workstation vendors
snapped them up.  They made it to the PC trade in the late '80s.)

Speed
-----
DRAMs are characterized by the time it takes to read a word,
measured from the row address becoming valid to the data coming out.
This parameter is called Row Access Time, or tRAC.  There are many
other timing parameters to a DRAM, but they scale with tRAC
remarkably well.  tRAC is measured in nanoseconds (ns).
A nanosecond is one billionth (10 e-9) of a second.

It's so difficult to control the semiconductor fabrication processes,
that the parts don't all come out the same.  Instead, their performance
varies widely, depending on many factors.  A RAM design which would
yield 50 ns tRAC parts if the fab were always tuned perfectly, instead 
yields a distribution of parts from 80 to 50.  When the plant is new,
it may turn out mostly nominal 70 ns parts, which may actually deliver 
tRAC between 60.1 ns and 70.0 ns, at 70 or 85 degrees Celcius and
4.5 volts power supply.  As it gets tuned up, it may turn out mostly 60 
ns parts and a few 50s and 70s.  When it wears out it may get less 
accurate and start yielding more 70s again.

RAM vendors have to test each part off the line to see how fast it is.  
An accurate, at-speed DRAM tester can cost several million dollars, and 
testing can be a quarter of the cost of the parts.  The finished parts 
are not marked until they are tested and their speed is known.


Q) 2.15  What happen to my 384k?

The memory between 640k and 1Meg is used for the BIOS, the video
aperture, and a number of other things.  With the proper memory
manager, DOS can take advantage of it.  Many systems, however, won't
identify its existence on boot.  This does not mean it isn't there.

Q) 2.16  How do I tell how big/fast my SIMMs are?

Individual DRAMs are marked with their speed after they are tested.
The mark is usually a suffix to the part number, representing tens of
nanoseconds.  Thus, a 511024-7 on a SIMM is very likely a 70 ns DRAM.
(vendor numbering scheme table to be added)

Q) 2.17  What speed SIMMs do I need?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

There is no reliable formula for deriving the required RAM speed from
the clock rate or wait states on the motherboard.  Do not buy a
motherboard that doesn't come with a manual that clearly specifies
what speed SIMMs are required at each clock rate.  You can always
substitute *faster* SIMMs for the ones that were called out in the
manual.  If you are investing in a substantial quantity of RAM,
consider buying faster than you need on the chance you can keep it
when you get a faster CPU.

That said, most 25 MHz and slower motherboards work fine with 80 ns
parts, most 33 MHz boards and some 40 MHz boards were designed for
70 ns parts, and some 40 MHz boards and everything faster require
60 ns or faster.  Some motherboards allow programming extra wait states
to allow for slower parts, but some of these designs do not really relax
all the critical timing requirements by doing that.  It's much
safer to use DRAMs that are fast enough for the no-wait or one-wait
cycles at the top end of the motherboard's capabilities.

Q) 2.18  Will 9 chip and 3 chip SIMMs work together?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

Almost always.  But there are exceptions.

1.  Some motherboards do not supply enough refresh address bits for a
4Mb x1 or a 1Mb x4 DRAM.  These old motherboards will not work with 4
MB 9-chip SIMMs or 1 MB 3-chip SIMMS.

2.  Some EL CHEAPO motherboards do not have proper terminations on the
lines which drive the DRAM array.  These boards may show only marginal
compatibility with various SIMMs, not working with all prefectly good
SIMMs you try, favoring SIMMs with parameters skewed towards one end
or another of the allowed ranges.  In some cases, most of the SIMMs
you happen to try might be 9-chip modules, and in other cases they
might be 3-chip modules.  A random selection of a dozen SIMMs might
lead you to conclude the motherboard doesn't "work" with 3-chip
modules, or with a "mixture" of 3-chip and 9-chip modules.

You might find the real solution is to use SIMMs one speed faster
than the manual calls for, because the particular motherboard design
just cuts too many things too close.

Q) 2.19  What are "single-sided" and "double-sided" 72-pin SIMMs?

[From: uwvax!astroatc!nicmad!madnix!zaphod (Ron Bean)]
 
   All 72-pin SIMMs are 32 bits wide (36 with parity), but
double-sided SIMMs have four RAS (Row Address Strobe) lines instead of
two. This can be thought of as two single-sided SIMMs wired in
parallel. But since there is only one set of data lines, you can only
access one "side" at a time.
 
   Usually, 1Mb, 4Mb, and 16Mb 72-pin SIMMs are single-sided, and 2Mb,
8Mb, and 32Mb SIMMs are double-sided. This only refers to how the
chips are wired-- SIMMs that are electrically "single-sided" may have
chips on both sides of the board.
 
   Most 486 motherboards use memory in banks of 32 bits (plus parity),
and may treat a double-sided SIMM as "two banks" (see your
motherboard's manual for details). Some can take four SIMMs if they're
single-sided, but only two if they're double-sided. Others can take
four of either type.
 
   Pentium (and some 486) motherboards use pairs of 72-pin SIMMs for
64-bit memory. Since double-sided SIMMs can only access 32 bits at a
time, you still need to use them in pairs to make 64 bits.

Q) 2.20  What does parity/ECC memory protect the system from?
[From: gnewman@world.std.com (Gary Newman)]

Memory errors are categorized as either "HARD" failures, or "SOFT"
failures.  Either form of failure can cause anything from an
unexplained system crash to a nice warning message saying:

    "soft error corrected at address 0x00343487 pattern 0x0004000"

The methods that have been developed to deal with these failures are
outlined here.

HARD ERRORS occur when one or more bits in a memory consistently read
back different data than is written to them.  There are a myriad of
causes for these failures including failed: memory cells, memory
chips, solder connections, SIMM socket connections, and circuit
traces.  Hard errors are signs of truly broken hardware and require
physical repair to correct.  If you are lucky, simply removing and
reinserting a SIMM in its socket is sufficient to make a better
connection.  Usually it means you have a bad memory chip or
motherboard.

SOFT ERRORS occur when one or more bits in a memory read back
different data than was written to them, BUT after rewriting the same
data the memory reads it back correctly.  In other words: the error is
transient and not reproducible.  Soft errors are usually intermittent
with anywhere from hours to years between occurrences.  There are two
design causes for soft errors, motherboard noise and internal DRAM
noise due to alpha particles or marginal circuits.  On a well designed
motherboard, noise does not cause measurable soft errors unless the
board is defective.

Both soft errors and hard errors can be caused by static electricity
damage or otherwise defective parts.  Unfortunately these problem
parts don't always cause instant hard errors. Failures can appear
weeks or months after initial damage as soft (due to degraded
performance) or hard errors.  "Burn in" (which is heavy exercise of
hardware for it's first few days) is a method used by manufacturers to
weed out these failures at the factory.

Users of computers can also "change the design" of their computer
without understanding the ramifications of what they are doing.
Adding "SIMM converters" to fit 30 pin SIMMs into a 72 socket,
decreasing the DRAM refresh rate, overclocking, and changing the DRAM
access timing all can push a design beyond allowable specifications.
The problems frequently show up as parity errors, or on a system
without parity just as system flakiness.

INTERNAL DRAM NOISE is caused by two different sources.  Marginal
circuits on the DRAM are one source that quality manufacturers nearly
always find at the factory through testing of the parts.  HOWEVER,
SOME MARGINAL DRAM MAKES IT TO MARKET!  The result is a part that
produces a soft error more often than normal (see below).  A system of
mine had such a part that produced a single bit error (always in the
same DRAM chip of a SIMM) once a month.

ALL DRAM PRODUCES SOFT ERRORS DUE TO ALPHA PARTICLES.  The plastic
packaging of the DRAM contains small amounts of radioactivity that
produce alpha particles.  These are energetic, fast moving, helium
atoms which are missing their electrons.  When an alpha particle
emitted by the packaging hits a sense line in the DRAM during a read
cycle, the noise it produces causes the sense amplifier to misread the
data.  Then, as with all DRAM, the memory cell is refreshed after
reading and the bad data becomes permanent.

Memory Error Likelyhood

In 1990, alpha particle induced soft errors occurred in 16 Mb computer
systems at the mean rate of roughly one error every 3 months.
Improved DRAM designs have greatly reduced that error rate so that
today the mean error rate in a 16 Mb system is roughly one bit error
every 16 years.  Note that since the errors only occur when memory is
being read, faster access rates to memory make for shorter times
between errors.  When a computer is idle, the only DRAM access is due
to infrequent memory refresh cycles.  When a program is constantly
reading from memory at the maximum memory bandwidth, bit errors occur
more frequently.

With computers DESIGNED to produce memory errors at a rate of roughly
one bit error per system per 16 years, manufacturers have been cutting
costs by not including "parity" memory with systems they sell.  THIS
ERROR RATE PRODUCES A SINGLE BIT ERROR DURING A TYPICAL THREE MONTH
WARRANTY IN 1.6 PERCENT OF ALL THE COMPUTERS SOLD!  There are two main
risks of using a system without parity memory.  One is that the
computer user will have no warning when a memory error (soft or hard)
has occurred, and the other is that side effects of the error may be
hard to isolate.  A single bit error can produce side effects such as:
a wrong result in a spreadsheet, erroneous data in a database, a bug
in the instructions of an application program or operating system
causing mysterious system crashes.

With 100 million computers in use today, we should expect roughly
6 million single bit errors per year.  Computer hardware and software
companies must receive thousands of "side effect" bug reports and
support calls due to memory errors alone.  The costs of NOT including
parity memory must be huge!


Q) 2.21  What happens if I get memory error with or without parity/ECC?
[From: gnewman@world.std.com (Gary Newman)]

Memory diagnostics and Power On Self Tests (POSTs) find only hard
errors WHEN THE USER LOOKS FOR THEM.  The POST only reports these
errors when a computer is booted.  So unless a memory diagnostic
program is run by the user, a hard memory error may go undetected
until the next reboot.  The effects of an error can spread far and
wide during that time.  Some systems BIOS allows the user to disable
POST to speed up reboot.  Beware that doing this can cause widespread
data corruption if a hard error is present on a system without parity
memory.

The ONLY method of finding hard or soft memory errors during operation
is the use of PARITY MEMORY.  This is simply the addition of one extra
bit for every byte of memory to the computer, increasing memory SIMM
costs by about 10% due to packaging economics.  For a 16 Mb memory
today parity adds about $50 to the end user price of the computer
system.  SOFTWARE CANNOT REPLACE THE FUNCTION OF PARITY MEMORY!

In its simplest form, hardware already in all computers manufactured
today uses information in the parity memory. This allows it to detect
any single bit memory errors before the computer can make any use of
the bad data.  Use of parity memory prevents the error from
propagating and producing side effects.  The only user unfriendly
aspect to this is that computers without ECC (see below) can only halt
the running program to prevent the use of the bad data.  However, that
is almost always better, and less costly, than allowing the spread of
bad data.

At its best, the OS on the computer system can display a warning that
a memory error occurred in a specific SIMM and that the program is
being halted.  This is typical for the Unix OS.  If the error occurs
in the OS itself, the whole system is halted.  The MSDOS operating
system appears to leave the problem to the system's BIOS to deal with.
The better BIOSs will display a message and halt.  The worst will
simply freeze.  All of these alternatives are better and less costly,
than allowing the spread of bad data.

It is interesting to note that Pentium computers access memory 64 bits
at a time, allowing use of Error Correcting Circuits (called ECC) when
parity memory is included.  The cost of adding ECC to the memory
interface chips is modest, and most server computers have done
this.  The result is that soft errors can not only be detected, but
also corrected on the fly without effecting the running programs.
Computers that do this produce warning messages such as:

    "soft error corrected at address 0x00343487 pattern 0x0004000" 

so you know which SIMM produced the error.  Frequent errors in the
same SIMM indicate a bad memory chip. That's how we found the SIMM
that produced one error a month for three months straight!  Single bit
hard errors can also be corrected on the fly.  A single burned out
memory bit or bad SIMM pin is "worked around" by the ECC.  No need to
fix it until a convenient time comes around.

What about errors that parity let's slip by?  Those are double bit
errors and are thus expected once every few thousand years.
Perhaps double bit errors will become important when there are
billions of computers in use... or gigabytes of DRAM on the average
computer.


Q) 2.22  Do I really need parity/ECC?
[From: gnewman@world.std.com (Gary Newman)]

Perhaps the lack of widespread knowledge about memory errors is the
cause of the near eradication of parity memory.  In that case, I hope
the above has helped spread the word about an inexpensive time, money,
and anxiety saver.

Computers based on the new Intel Triton chipset CANNOT DETECT MEMORY
ERRORS.  In other words, Intel chose to not support parity memory with
this chipset.  Beware that buying a system based on Triton will leave
you no future way to add parity error detection to your system.

For any computer system where it's worth spending $50 to avoid the
annoying, and possibly quite damaging, effects of memory errors PARITY
MEMORY IS A MUST.

On some computer systems the owner is willing to take some pain in
order to save the $50 that parity memory adds in costs.  If your
computer will be used solely to play games or you don't mind
occasionally having corrupt files or flaky programs then you may want
to consider a system which has no memory error detection.


Q) 2.23  How do I get a system with parity support?
[From: gnewman@world.std.com (Gary Newman)]

Once you've decided you want a computer that supports parity error 
detection, you will find that nearly all mainstream mail order systems 
are not available with it.  Here are a few approaches that work.

Buy a corporate or server system advertised with parity support.
Dell Optiplex, HP Vectra, and others are available, but usually at a
"corporate" priced premium of $600 or so.

Buy from a local system builder who will provide parity support.

Purchase a system with parity support but without parity SIMMs.
All intel Neptune based P5 computers have such support. Then swap out
the non-parity SIMMs after replacing them with parity simms you purchased from
one of the many memory vendors.  Then the non-parity SIMMs can be
either sold to vendors who resell, or put in a game system you may
have hanging around.


Q) 2.24  How do you distinguish between parity and non-parity SIMMs?

The precise method is to count the number and type of each chip (after
looking them up in a databook for that DRAM manufacturer).  However,
you can get a good guess just by counting the number of chips.

DRAMs (for PC SIMMs) are either 1 or 4 bits wide.  The total bit width
is 8 or 9 (for 30 pin SIMMs) and 32 or 36 (for 72 pin SIMMs).  DRAMs
to hold parity are usually 1 bit wide to allow byte writes.  Some
examples:

2 chips: 8 bit (2x4bit) - no parity
3 chips: 9 bit (2x4bit + 1x1bit) - parity
8 chips: 8 bit (8x1bit) or 32 bit (8x4bit) - no parity
9 chips: 9 bit (9x1bit) - parity
12 chips: 36 bit (8x4bit + 4x1bit) - parity

Some new 72 pin SIMMs have two 32 (or 36) bit banks per SIMM and
therefore have double the number of chips as a normal SIMM.

It also seems that some cheap SIMMs have begun using 'fake' parity on
SIMMs; XOR gates that generate parity from 8 bit data rather than
store and recall the actual parity generated by the DRAM controller.
The only way to tell if you've been taken by one of these fake parity
SIMMs is to look up all of the suspected parts in a DRAM databook.

Q) 2.25  Can I use Mac or PS/2 SIMMs in my PC?

Yes, just about all SIMMs are compatible, be they from another
personal computer, a mainframe, or even a laser printer, though are a
few some odd systems out there.  There are three significant issues:
speed, parity and number of pins (data width).  Speed is obvious,
check the rating, ie: 70ns, to make sure they meet the minimum
requirements of your system.  Parity either exists or doesn't exist
and can be identified by an extra bit per byte, ie: 9 bits or 36 bits.
If your system does not require parity, you can still use SIMMs with
parity.  If, however, your system does require parity, you can't use
SIMMs without parity.  For this case, many PC's have an option to
disable the parity requirement via a jumper or BIOS setting; refer to
your motherboard manual.  The final issue is the number of pins on the
SIMM; the two most common are 30 pins (8 or 9 bit SIMMs) and 72 pins
(32 or 36 bit SIMMs); the second is physically larger thus the one can
not be used in the other.  A few motherboards have both types of
sockets.

Q) 2.26  What do wait states and burst rates in my BIOS mean?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

Modern motherboards are equipped with variable clocks and features
for tuning board performance at each speed.  The BIOS knows how to
program the register bits which control these options.

1.  Wait states may be adjustable to allow for slower DRAMs or
cache RAMs.  If you don't have a motherboard manual, or it doesn't
say, then you will just have to experiment.
2.  Sometimes a wait or two on a write is required with write-through
cache.  The programming allows for slower DRAMs.  The extra wait
state may cost you enough time that you would do better running at a
slower clock rate where the wait state is not required.
3.  Burst rates refer to the number of wait states inserted for
each longword access in the cache fill cycle.

Bob Nichols (rnichols@ihlpm.ih.att.com) adds:
These numbers refer to the number of clock cycles for each access of a
"burst mode" memory read.  The fastest a 486 can access memory is 2 clock
cycles for the first word and 1 cycle for each subsequent word, so
"2-1-1-1" corresponds to "zero wait states."  Anything else is slower.

How fast you can go depends on the external clock speed of your CPU, the
access time of your cache SRAMs, and the design of the cache controller.
It can also be affected by the amount of cache equipped, since "x-1-1-1"
is generally dependent on having 2 banks of cache SRAMs so that the
accesses can be interleaved.  With a 50MHz bus (486DX-50), few
motherboards can manage "2-1-1-1" no matter how fast the SRAMs are.  At
33MHz or less (486DX-33, 486DX2-66), many motherboards can achieve
"2-1-1-1" if the cache SRAMs are fast enough and there are 2 banks
equipped (cache sizes of 64KB or 256KB, typically).

Q) 2.27  Cache terminology, what does it mean?
[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

Why cache improves performance
------------------------------
Today's microprocessors ("uPs") need a faster memory than can be made
with economical DRAMs.  So we provide a fast SRAM buffer
between the DRAM and the uP.  The most popular way to set it up is
by constructing a "direct mapped cache," which is the only setup
I'll describe here.


Generic motherboard cache architecture
--------------------------------------
The direct mapped cache has three big features:
1. a "data store" made with fast SRAMs,
2  a "tag store" made with even faster SRAMs, and
3. a comparator.

The data store is the chunk of RAM you see in the motherboard price
lists.  It holds "blocks" or "lines" of data recently used by the CPU.
Lines are almost always 16 bytes.  The address feeding the cache is
simply the least significant part of the address feeding main memory.
Each memory location can be cached in only one location in the data
store.

There are two "policies" for managing the data store.  Under the
"write-back" (or "copy-back") policy, the master copy of the data is
in cache, and main memory locations may be "stale" at times.  Under
"write-through", writes go immediately to main memory as well as to
cache and memory is never "stale."

The tag store mantains one "word" of information about each line of
data in the data store.
In a "write-back" or "copy-back" cache, the tag word contains two items:
1.  the part of the main memory address that was *not*
    fed to the data store, and
2.  a "dirty" bit.

A write-through cache doesn't need a dirty bit.  The tag store is
addressed with the most significant address bits that are being fed to
the data store.  The tag is only concerned with the address bits that
are used to select a line.  With a 16 byte line, address bits 0
through 3 are irrelevant to the tag.

An example: The motherboard has 32 MB main memory and 256 KB cache.
To specify a byte in main memory, 25 bits of address are required: A0
through A24.  To specify a byte in data store, 18 bits (A0 through
A17) are required.  Lines in cache are 16 bytes on 16 byte boundaries,
so only A4 through A17 are required to specify a line.  The tag word
for this system would represent A18 through A24 (plus dirty bit).  The
tag store in this system would be addressed by A4 through A17,
therefore the tag store would require 16 K tag words seven bits wide.
The dirty bit is written at different times than the rest of the tag,
so it might be housed separately, and this tag store might be built in
three 16K x4 SRAMs.

What happens when it runs
-------------------------
Each motherboard memory cycle begins when the uP puts out a memory
address.  The data store begins fetching, and simultaneously the
tag begins fetching.  When the tag word is ready, the Comparator
compares the tag word to the current address.

If they match, a cache hit is declared and the uP reads or writes
the data store location.  If the hit is a write, the copy-back
cache marks the line "dirty" by setting its dirty-bit in the line's
tag word.  The write-through motherboard simultaneously stores the
write data in data store and begins a DRAM write cycle.  The uP
moves on.

If the tag word doesn't match, what a bummer, it's a cache miss.
If the line in cache is dirty, double bummer, the line must be
copied back to main memory before anything else can happen.  All
16 bytes are copied back, even if the hit was a one-byte write.
This data transfer is called a "dirty write flush."

On a read-miss, the motherboard has to copy a line from main memory
to cache (and update the tag, the whole operation is called a "cache
fill"), and the uP can stop waiting as soon as the bytes it wants
go by.  On a write-miss, the caches I've worked with ignore the
event (that's an oversimplification) and the main memory performs
a write cycle.  I've heard of systems that fill on a write-miss,
that is they replace the cache line whenever it misses, read or
write, dirty or not.  I've never seen such a system.

Terms
-----
The 486, the 68020, and their descendants have caches on chip.
We call the on-chip cache "primary" and the cache on the
motherboard "secondary."  The 386 has no cache, therefore the cache
on a 386 motherboard is "primary."  I like to call the DRAM array
"core" for brevity.  Motherboard = "mb."  Megabyte = "MB."

Problems
--------
I added "core" and I had to disable my secondary cache to
get the board running.  Or, I added core and performance took a dive.
Disabling secondary cache improved it, but still real slow.
What happened?

 Whenever you are adding memory and you cross a power-of-2
address boundary, another address bit becomes interesting to the
tag.  That is, the tag does not care when you add your 8th MB
(MB) but it cares a lot about the new address bit 24 when you add
your 9th MB, or your 17th (bit 25).  Evidently, at the low-price
end of the mb market there are boards with not enough tag RAM
sockets to support all the core they can hold.  Most of these EL
CHEAPO mbs don't even try to use cache in the region beyond the
tag's coverage.  Some of them don't have the logic to stay out or
the BIOS doesn't know to enable it.  These boards just don't run
right.

Do not buy a mb if you are not sure it can cache all of core.  The
worst case is with core fully stuffed with whatever the board claims
to hold, and the smallest cache configuration.  Some motherboards
ask you to add cache when you add core, so that they don't have to
provide for that worst case tag width.  These motherboards may ask
you to move some jumpers in the tag area.  The jumpers control
which address bits the tag looks at.  Do not buy a motherboard if
you don't know how to set all the jumpers.


Q) 2.28  How do I upgrade the size of my cache?

Look in your motherboard manual.  Each motherboard is different.
You will have to add or replace cache RAMs and move jumpers.

Q) 2.29  Do I need to fill the "dirty tag" RAM socket on my motherboard?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

Perhaps you don't *have* to for the board to run, but the missing RAM
will cost you performance.  Most "write-back" mbs cope with the
missing RAM by treating all lines as dirty.  You get a lot of
unneccessary write cycles; you might even do better with
write-through.

Your bargain-basement no-documentation no-brand mb might not have the
pullup resistor on that socket, and it might run for a second, ten
minutes, or ten years with that pin not driven.  I think it's a
pointless risk to leave the socket empty.

Q) 2.30  How fast do my cache RAMs have to be?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

Only the person who designed your mb knows for sure.  There is
no simple formula related to clock rate.  However, most people tell
me their 33 MHz mbs' manuals call for 25 ns data store and 20 ns
tag store, and their 40 and 50 MHz mbs want 20 ns data store and
15 or 12 ns tag.  Tqhe tag has to be faster than data store to make
time for the comparator to work.  Do not buy a motherboard if you do
not know what speed and size of cache RAMs it requires in all its
speeds and configurations.

If you're not sure, it doesn't hurt to use faster RAMs than your
manual calls for.  If your manual says 20 ns for location x and you
happen to have 15 ns parts, it's ok to "mix" the speeds.  It's ok to
"mix" RAMs from more than one manufacturer.  However, the faster RAMs
will not buy you more performance.

Q) 2.31  Which is the best cache policy, write-through or "write-back?"

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

For most applications, copy-back gives better performance than
write-through.  The amount of win will depend on your application and
may not be significant.  Write-through is simpler, but not by much any
more.

Q) 2.32  What about an n-way set associative cache, isn't it better?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

At the high end of the mb market, caches are available with more than
one set.  In these caches, the data store is broken into two or four
parts, or sets, with a separate tag for each.  On a miss, clever
algorithms (such as Least Recently Used) can be used to pick which set
will be filled, because each set has a candidate location.  The result
is a higher hit rate than a direct mapped (single set) cache the same
size can offer.

The primary cache on the 486 is four-way set associative.

Q) 2.33  Which is better, ISA/EISA/VLB/PCI/etc?
[From: ralf@wpi.wpi.edu (Ralph Valentino)]

Here is a quick overview of the various bus architectures available
for the PC and some of the strengths and weaknesses of each.  Some
terms are described in more detail at the bottom.

XT bus:
        8 data bits, 20 address bits
        4.77 MHz
   Comments: Obsolete, very similar to ISA bus, many XT cards will
             work in ISA slots.
        
ISA bus: Industry Standard Architecture bus (aka. AT bus)
        8/16 data bits, 24 address bits (16Meg addressable)
        8-8.33MHz, asynchronous
        5.55M/s burst
        bus master support
        edge triggered TTL interrupts (IRQs) - no sharing
        low cost
   Comments: ideal for low to mid bandwidth cards, though lack of
             IRQs can quickly become annoying.
        
MCA bus: Micro Channel Architecture bus
        16/32 data bit, 32 address bits
        80M/s burst, synchronous
        full bus master capability
        good bus arbitration
        auto configurable
        IBM proprietary (not ISA/EISA/VLB compatible)
   Comments: Since MCA was proprietary, EISA was formed to compete with
             it.  EISA gained much more acceptance; MCA is all but dead.
        
EISA bus: Enhanced Industry Standard Architecture bus
        32 data bits, 32 address bits
        8-8.33MHz, synchronous
        32M/s burst (sustained)
        full bus master capability
        good bus arbitration
        auto configurable
        sharable IRQs, DMA channels
        backward compatible with ISA
        some acceptance outside of the PC architecture
        high cost
   Comments: EISA is great for high bandwidth bus mastering cards
             such as SCSI host adaptors, but its high cost limits
             its usefulness for other types of cards.

P-EISA: Pragmatic EISA (also Super-ISA)
        (see the description of the HiNT chipset elsewhere in this FAQ)

VLB: VESA Local Bus
        32 data bits, 32 address bits
        25-40MHz, asynchronous
        130M/s burst (sustained is closer to 32M/s)
        bus master capability
        will coexist with ISA/EISA
        slot limited to 2 or 3 cards typical
        backward compatible with ISA
        moderate cost
   Comments: VLB is great for video cards, but its lack of a good bus
             arbiter limits its usefulness for bus mastering cards and
             its moderate cost limits its usefulness for low to mid 
             bandwidth cards.  Since it can coexist with EISA/ISA, a
             combination of all three types of cards usually works best.
             
PCI:  Peripheral Component Interconnect local bus
        32 data bits (64 bit option), 32 address bits (64 bit option)
        up to 33MHz, synchronous (upto 66MHz PCI 2.1 option)
        132M/s burst at 33MHz (sustained) (264M/s with 64 bit option)
        full bus master capability
        good bus arbitration
        slot limited to 3 or 4 cards typical
        auto configurable
        will coexist with ISA/EISA/MCA as well as another PCI bus
        strong acceptance outside of the PC architecture
        support for 5V and 3.3V peripheral cards
        moderate cost
   Comments: The newest of the buses, combining the speed of VLB with
             the advanced arbitration of EISA.  Great for both video
             cards and bus mastering SCSI/network cards.  
   Notes: 64 bit option was defined in the original PCI 2.0 spec.  66MHz
          operation is an option of the PCI 2.1 spec and is only
          available for the 3.3V PCI bus.  PCI 2.1 compliance does NOT imply
          66MHz operation.

                        =Terms=

Auto configurable:  Allows software to identify the board's
requirements and resolve any potential resource conflicts
(IRQ/DMA/address/BIOS/etc).

Bus master support:  Capable of First Party DMA transfers.

Full bus master capability:  Can support any First Party cycle from any
device, including another CPU.

Good bus arbitration:  Fair bus access during conflicts, no need to
back off unless another device needs the bus.  This prevents CPU
starvation while allowing a single device to use 100% of the available
bandwidth.  Other buses let a card hold the bus until it decides to
release it and attempts to prevent starvation by having an active card
voluntarily release the bus periodically ("bus on time") and remain
off the bus for a period of time ("bus off time") to give other
devices, including the CPU, a chance even if they don't want it.

16Meg addressable:  This limits first party DMA transfers to the lower
16 Meg of address space.  There are various software methods to
overcome this problem when more than 16 Megs of main memory are
available.  This has no effect on the ability of the processor to
reach all of main memory.

Backward compatible with ISA:  Allows you to place an ISA card in the
slot of a more advanced bus.  Note, however, that the ISA card does
not get any benefit from being in an advanced slot, instead, the slot
reverts to an ISA slot.  Other slots are unaffected.


Q) 2.34  *What are the (dis)advantages of ISA/VLB/EISA SCSI?

Q) 2.35  Will an ISA card work in an MCA (PS/2) machine?

No, they will not.  MCA, unlike EISA and VLB, is not backward
compatible with ISA.

Q) 2.36  What does the "chip set" do?
[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

The motherboard "chip set" contains all the logic that's not in
the microprocessor ("uP") and its coprocessor, or the memory.
These functions always include:
 *  Address decoding and "memory mapping"
 *  keyboard interface controller (which includes reset generator)
 *  Direct Memory Access (DMA) channels
 *  interrupt controller
 *  bus controller(s)
 *  battery-powered "real time" clock/calendar circuit
 *  crystal-controlled clock oscillator(s)
 *  main memory controller
 
They almost always include:
 *  controller for cache external to the uP
 *  "turbo" switch logic
 *  programmable "wait state" logic

and some of them include:
 *  controller(s) for PCMCIA slots
 *  "green" power-conservation logic
 *  video display logic for CRT, LCD, or both
 *  serial ports, parallel ports, floppy, SCSI and/or IDE, etc. controllers
 *  network interface controllers (for Ethernet)

Some people consider the BIOS ROM part of the "chip set."

Sometimes part of an EISA or VLB bus controller is implemented
in an optional, socketed integrated circuit.  A motherboard like that
can be sold with the socket empty, and you have to go back and
buy the "bus mastering option" later when you find out you need it.

"Chip sets" are usually a set of highly integrated, special purpose
integrated circuits.  The keyboard interface controller is usually
in a 40-pin dual-inline pin (DIP) package compatible with the Intel
8048 single-chip microcomputer which was used for that function in the
IBMPC-AT.  The rest of the logic often fits in a single IC.  In the trade,
you may see this single IC referred to as "the chipset," even though
the keyboard interface and other logic is external.  The Asian data sheets
often call the high-integration chips "LSIs."

The word "ChipSet" is a trademark of Chips and Technologies
Inc. (San Jose, California), which introduced a 5-chip set of LSIs
for AT-clone motherboards in early 1985.  CTI may also own "chipset"
and "Chipset"; I don't know.
CTI was very successful at promoting the term "ChipSet," but less
successful at associating it in the public mind with their particular
brand.  People use the word to refer to any high integration chip
used in PCs.  For example, you'll hear people talk about the "ET4000
video chipset."  The ET4000 is a single chip which integrates most
of an SVGA controller.  The word "ASIC" (application-specific integrated
circuit) would be more appropriate.

Single, high-integration ICs are not very good at driving heavily
loaded signals, like the ones in the memory array and the expansion
slots.  Better motherboards use buffer chips external to the LSI
for this electrical function.  It may not show up in "WinMark"
comparisons, but it shows in electrical compatibility.  Well-buffered
motherboards are less likely to require SIMM "cherry-picking,"
and are more likely to work at high ambient temperatures.
The 74F245, which costs about 15 cents in high volume, is often used for
this electrical buffering.


Q) 2.37  How do I enter the CMOS configuration menu?

[From: burnesa@cat.com (Shaun Burnet)]

        AMI BIOS        Del key during the POST
        Award BIOS      Ctrl-Alt-Esc
        DTK BIOS        Esc key during the POST
        IBM PS/2 BIOS   Ctrl-Alt-Ins after Ctrl-Alt-Del
        Phoenix BIOS    Ctrl-Alt-Esc or Ctrl-Alt-S

[From: mike@pencom.com (Mike Heath)]

Some 286 machines don't have a CMOS configuration menu in the BIOS.
They require a software CMOS setup program.  If you don't have the
Installation and/or Diagnostics diskette for your machine, you can
try using a shareware/freeware program.  Try looking in:

oak.oakland.edu:/SimTel/msdos/at
  or
ftp.uu.net:/systems/msdos/simtel/at


Q) 2.38  What is bus mastering and how do I know if I have it?

Bus mastering is the ability of an expansion (ISA/EISA/VLB/MCA/etc)
card to directly read and write to main memory.  This allows the CPU
do delegate I/O work out to the cards, freeing it to do other things.
For all of the above busses, bus mastering capability is assumed.
Unless specifically stated otherwise, you should assume each slot has
this capability.  For cards, this is not assumed.  If you want a bus
mastering card, you should specifically request it and expect to pay
more.  Note that some cards (RLL/MFM/IDE/com) are not available in bus
mastering versions.

Q) 2.39  Can I put an ISA cards in EISA or VLB slots?

Yes, you can put ISA cards in both EISA slots and VLB slots, as both
buses were specifically designed to be 100% ISA compatible.  ISA cards
will not directly effect the performance of EISA/VLB cards; a well
balanced system will have both.  Note, however, that the total
bandwidth of the bus will be split between all cards, so there is a
strong advantage to using EISA/VLB cards for the high bandwidth
devices (disk/video).

Q) 2.40  How should I configure ISA/VLB cards in the EISA config utility?

Only EISA cards matter in the ECU; ISA and VLB entries are only place
markers.  While this is a good way to keep track of IRQ, DMA and BIOS
conflictions, ISA and VLB need not be placed in the configuration at
all, nor should it be assumed that the settings for them match the
actual card settings.  If you wish to add them, you can use the
"Generic ISA Card" configuration file for either.  Do not expect card
vendors to supply them.

Q) 2.41  What is the difference between EISA Standard and Enhanced modes?

Many EISA cards support both Standard (ISA) and Enhanced (EISA) modes.
In Standard mode, the card will appear to be an ISA card to the OS; it
will generate edge triggered interrupts and only accept ISA addressing
(for bus mastering cards), for instance.  An important thing to note
is that the card may still do EISA specific things like 32-bit data
bus mastering and EISA configuration setup as this functionality is
hidden from the OS.

Q) 2.42  Is there any point in putting more than 16M in an ISA machine?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

Sure.  Even inferior operating systems can use it for something.
The question is how much performance it buys.  In ISA, the DMA
channels and bus-mastering IO cards can only address the first 16 MB.  
Therefore the device drivers have to copy data up and down or just
not use the space.  I am told the Linux SCSI drivers know how to
do this.  I don't know about OS/2 or MSWindows.

Q) 2.43  What disadvantages are there to the HiNT EISA chip set?
[From: ralf@wpi.wpi.edu (Ralph Valentino)]

The HiNT Caesar Chip Set (CS8001 & CS8002) can come in three different
configurations.  All three of these configurations have EISA style
connectors and are (sometimes incorrectly) sold as EISA motherboards.
The differences should be carefully noted, though.

The rarest of these configuration uses a combination of the first HiNT
chip (CS8001) and the Intel chip set.  This configuration can support
the full EISA functionality: 32 address bits, 32 data bits, level
sensitive (sharable) interrupts, full EISA DMA, watch dog (sanity)
timer, and so forth.

The second configuration is called Super-ISA, which uses both of the
HiNT chips.  This configuration is very common in low-end models.  It
supports a very limited functionality: 24 address bits, 32 data bits,
edge triggered (non-sharable) interrupts, ISA (16 data, 24 address)
DMA, and no watch dog timer.  Some EISA boards, such as the Adaptec
1742A EISA Fast SCSI-2 host adapter, can be configured to work in this
mode by hacking their EISA configuration file (.CFG) to turn off these
features.  Other EISA cards require these features and are therefore
unusable in these systems.

The final configuration is called Pragmatic EISA, or P-EISA.  Like
Super-ISA, both HiNT chips are used but external support logic
(buffers and such) are added to provide a somewhat increased
functionality: 32 address bits, 32 data bits, edge triggered
(non-sharable) interrupts, ISA (16 data, 24 address) DMA, and no watch
dog timer.  The full 32 bits for address and data allow bus mastering
devices access to the complete range of main memory.  As with
Super-ISA, there may be incompatibilities with some EISA cards.


Q) 2.44  *Should I change the ISA bus speed?

Q) 2.45  Why is my PC's clock so inaccurate?
[From: uwvax!astroatc!nicmad!madnix!zaphod (Ron Bean)]
 
Usually this means that the clock crystal is not adjusted properly, or
that it needs a new battery. The interrupt-based "DOS time" can also
be affected by programs that disable interrupts for too long.
 
   If your clock is just running at the wrong speed, you can
compensate for it in software by measuring the drift rate and applying
a correction factor. In the long run, this can be *very* accurate. One
such program for DOS is adclk100.zip. An alternative is to run a
program that periodically sets your clock to another one that's known
to be accurate (see the question on setting your clock).
 
   If your clock is more erratic (eg, it stops when the machine is
turned off, or the date gets scrambled), try replacing the battery
(but remember to write down your CMOS settings first!).  The CMOS RAM
takes considerably less power than the clock, so it may keep working
even though the battery is too weak to run the clock (see the question
on replacing the battery for details).
 
   A typical cheap quartz watch is rated at +/- 15 sec per month (3
minutes per year) which is about 5.7 ppm (parts per million).  Dallas
Semiconductor rates their encapsulated clock modules for +/- 1 min per
month, or 22.8 ppm. Clocks with external crystals can be "fine-tuned"
with a trimmer capacitor-- if the motherboard designer included one
(Note: there may be more than one crystal on the motherboard). The
crystal's frequency will change slightly over time as the crystal
"ages".
 
   The original IBM AT used the Motorola MC146818, which is a
real-time clock plus 50 bytes of CMOS RAM. This chip is discussed in
the book "The Undocumented PC", from Addison-Welsey. The Dallas
Semiconductor DS1285 is a drop-in replacement for the MC146818, and
the DS1287 is the same chip encapsulated with its own battery and
clock crystal. Other variants include larger amounts of CMOS RAM. Most
software accesses the clock through the BIOS.
 
   Before the AT, there were various types of aftermarket clock cards,
and some of them may still be available (even though every PC sold in
the last several years "already has a clock").
 
   Given the number of times this comes up on the net, there should be
a market for accurate clock cards. On the other hand, most people
don't seem to care whether their computers have anything close to the
correct time. If your machine doesn't keep time correctly, and you
think it should, you might consider complaining to the manufacturer
about it.


Q) 2.46  How can I automatically set my PC's clock to the correct time?
[From: uwvax!astroatc!nicmad!madnix!zaphod (Ron Bean)]

If you're on the internet, you can use ntp (network time protocol) to
set your clock to another machine that's known to be accurate (see RFC
1129, Internet Time Synchronization).
 
   ACTS, the Automated Computer Time Service, is available by modem at
(303)494-4774 (note this is NOT a toll-free call). There are programs
that will dial this number and set your clock automatically. This
service is run by NIST (the National Institute of Standards and
Technology, formerly the National Bureau of Standards).
 
   In Germany, the Physikalisch-Technische Bundesanstalt (PTB)
broadcasts a coded time signal on 77.5 kHz from a transmitter near
Frankfurt, and inexpensive receivers are available that can plug into
a serial port (this signal should cover most of Europe). In the US,
NIST runs a similar station (WWVB) on 60 kHz, but the data is encoded
differently and receivers are expensive and hard to find.
 
   Other coded time signals are available from WWV and WWVH on 2.5, 5,
10, 15, and 20 MHz (shortwave), and from the GOES and GPS
satellites. CHU Canada on 3.33, 7.335, and 14.670 MHz broadcasts time
codes using Bell 103 FSK (300 baud modem tones) during seconds 31
through 39 of each minute. If you don't have a shortwave receiver, the
WWV audio time announcement can be heard by dialing (303)499-7111
(again, this is NOT a toll-free call).
 
   NIST publishes a 30-page booklet (NIST Special Publication 432)
that explains all of their time services in detail. They also have a
partial list of companies that make receivers, but it appears to be
somewhat out of date. Both are available from:
 
          NIST/Radio Station WWV
          2000 East County Road 58
          Fort Collins, CO  80524-9499
 
   You may have heard about Heathkit's "Most Accurate Clock", which
decodes the time signal from WWV and has a serial port.  Heath no
longer sells kits, but they still sell the factory-built version of
the clock (it's not cheap, though). Their address is P.O. Box 1288,
Benton Harbor, MI 49023.


Q) 2.47  What is the battery for and how do I replace it?

[From: uwvax!astroatc!nicmad!madnix!zaphod (Ron Bean)]

   The battery maintains power to the CMOS RAM and the real-time clock
when your PC is turned off. You may have a small lithium "coin"
battery soldered to the motherboard, or a larger external one plugged
into a connector. Some motherboards have a jumper to select either
type, and a few have a NiCd battery that recharges automatically, or a
lithium battery encapsulated in the clock chip.
 
   NOTE: Always write down your CMOS settings before you mess with the
battery! In fact, you should write them down now anyway, in case the
battery fails later.
 
   The batteries that are soldered in or encapsulated with the clock
chip are supposed to last 10 years or more, but your mileage may
vary. Some people find that the external type has to be replaced every
couple of years. Self-recharging NiCds that get power from a disk
drive cable are available as aftermarket items.  A few people have
tried to save money by substituting 4 alkaline AA batteries for the
expensive external lithium battery, but they have to be replaced more
often.
 
   If you need to replace a soldered-in battery, have a repair shop
install a socket (you shouldn't attempt this yourself, unless you're
experienced at soldering on expensive multi-layer circuit boards). If
the battery is encapsulated in the chip, there is no way to replace it
without replacing the chip-- again, consult a repair shop if it's not
socketed. These chips can be "turned off" via software to extend
battery life during storage, and are shipped from the factory that
way.

Q) 2.48  Can I use IRQ2 or is it special?

IRQ2 is used to cascade the second programmable interrupt controller
(PIC) on AT machines.  The IRQ2 line on the old XT bus has been
renamed to IRQ9.  This has one and only one side effect: from a
software point of view, IRQ2 = IRQ9.  You can freely use IRQ2 on any
hardware device, provided you are not already using IRQ9.  Your
associated software driver can be set to IRQ2 or IRQ9, which ever it
happens to prefer.  Note that many video cards have an IRQ2 enable
jumper for very, very old backward compatibility reasons; you should
disable this before attempting to use the IRQ for something else.
There are no unexpected side effects.

Q) 2.49  Where do all the IRQ's and DMA Channels go?
[From: wlim@lehman.com (Willie Lim)]
[From: r.j.mersel@is.twi.tudelft.nl (Rob Mersel)]

(Note that DRQ is the DMA Channel)

Default IRQ/DRQ settings AT systems:

IRQ   IO BASE   DRQ   Card or Device
      ADDRESS
      (HEX)
===   =======   ===   ================
 *       *       0    unassigned (? bit DMA)
 *       *       1    unassigned (8 bit DMA)
 *       *       3    unassigned (8 bit DMA)
 *       *       5    unassigned (16 bit DMA)
 *       *       6    unassigned (16 bit DMA)
 *       *       7    unassigned (16 bit DMA)
 0       *       *    timer (reserved)
 1       *       *    keyboard (reserved)
 2       *       *    interrupt 8-15 (cascade) (see Q 2.40)
 3    2E8-2EF    *    COM4:
 3    2F8-2FF    *    COM2:
 4    3E8-3EF    *    COM3:
 4    3F8-3FF    *    COM1:
 5    278-27F    *    LPT2:
 6    3F0-3F7    2    Floppy drive controller
 7    378-37F    *    LPT1: (PRN:)
 8       *       *    real-time clock (reserved)
 9       *       *    unassigned (see Q 2.40)
10       *       *    unassigned
11       *       *    unassigned
12       *       *    unassigned
13       *       *    math co-processor
14    1F0-1F7    *    Hard drive controller (drive 0)
14    3F6-3F7    *    Hard drive controller (drive 1)
15    170-177    *    Secondary hard drive controller (drive 2)
15    376-377    *    Secondary hard drive controller (drive 3)


Adapter card IRQ/DRQ settings:

IRQ   IO BASE   DRQ   Card or Device
      ADDRESS
      (HEX)
===   =======   ===   ================
 *    200-207    *    Game port
 2      330      *    MPU-401 Emulation (PAS 16)
 3      300      *    3Com Etherlink II, II/TP, II/16, II/16TP, 16/16TP
 3      300      *    Novell NE2000
 3      300      *    SMC/Western Digital 8003EP, 8013EWC, 8013WB
 5      368      *    Ungermann-Bass Ethernet NIUpc (long), NIUpc/EOTP (short)
 5      ???      *    DEC etherWORKS LC, Turbo, Turbo/TP
 5      220      1    Sound Blaster Emulation (PAS 16)
 5    220-22F    1    Sound Blaster 2.0 (default)
 *    338-339    *    Sound Blaster 2.0 FM music chip
 5      A20      5    Proteon P1390
 7       *       3    Pro Audio Spectrum 16 (PAS 16)
 9      300      5    Boca Ethernet BEN100, BEN102, BEN300


Default IRQ/DRQ settings XT systems:

IRQ   IO BASE   DRQ   Card or Device           
      ADDRESS
       (HEX)
===   =======   ===   ===============
 *       *       0    DRAM-refresh (used on motherboard only?)
 *       *       1    unassigned
 0       *       *    timer (reserved)
 1       *       *    keyboard (reserved)
 2       *       *    unassigned
 3    2E8-2EF    *    COM4:
 3    2F8-2FF    *    COM2:
 4    3E8-3EF    *    COM3:
 4    3F8-3FF    *    COM1:
 5       ?       3    Hard drive controller
 6    3F0-3F7    2    Floppy drive controller
 7    378-37F    *    LPT1: (PRN:)


===============
Ralph Valentino (ralf@fs09.webo.dg.com) (ralf@wpi.edu)
Senior Hardware Engineer, AViiON System Development
Data General Corporation, Westboro, MA USA


From David.Steele@usask.ca Thu May 02 10:30:39 1996
Path: tribune.usask.ca!rover.ucs.ualberta.ca!unixg.ubc.ca!van-bc!news.rmii.com!newsjunkie.ans.net!newsfeeds.ans.net!howland.reston.ans.net!newsfeed.internetmci.com!in1.uu.net!news.ultranet.com!bigboote.WPI.EDU!bigwpi.WPI.EDU!ralf
From: ralf@chpc.org (Ralph Valentino)
Newsgroups: comp.sys.ibm.pc.hardware.video,comp.sys.ibm.pc.hardware.comm,comp.sys.ibm.pc.hardware.storage,comp.sys.ibm.pc.hardware.cd-rom,comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.hardware.networking,comp.sys.ibm.pc.hardware.chips,comp.sys.ibm.pc.hardware.misc,comp.answers,news.answers
Subject: comp.sys.ibm.pc.hardware.* Frequently Asked Questions (FAQ) Part 2/5
Followup-To: comp.sys.ibm.pc.hardware.misc
Date: 19 Apr 1996 04:48:00 GMT
Organization: Worcester Polytechnic Institute
Lines: 1397
Approved: news-answers-request@MIT.EDU
Distribution: world
Expires: 31 May 1996 00:00:00 GMT
Message-ID: <4l75u0$elt@bigboote.WPI.EDU>
Reply-To: ralf@wpi.edu
NNTP-Posting-Host: bigwpi.wpi.edu
Summary: This is a monthly posting containing a list of Frequently
         Asked Questions (and their answers) pertaining to hardware
         and IBM PC clones.  It should be read by anyone who wishes
         to post to any group in the comp.sys.ibm.pc.hardware.*
         hierarchy.
Originator: ralf@bigwpi.WPI.EDU
Xref: tribune.usask.ca comp.sys.ibm.pc.hardware.video:68145 comp.sys.ibm.pc.hardware.comm:18558 comp.sys.ibm.pc.hardware.storage:68436 comp.sys.ibm.pc.hardware.cd-rom:32293 comp.sys.ibm.pc.hardware.systems:37510 comp.sys.ibm.pc.hardware.networking:12904 comp.sys.ibm.pc.hardware.chips:79432 comp.sys.ibm.pc.hardware.misc:60033 comp.answers:18185 news.answers:69819

Archive-name: pc-hardware-faq/part2
Last-modified: 1996/04/10
Version: 1.19

S) 3.0 IO controllers/interfaces

Q) 3.1  *How do IDE/MFM/RLL/ESDI/SCSI interfaces work?

Q) 3.2  How can I tell if I have MFM/RLL/ESDI/IDE/SCSI?

[From: ralf@wpi.edu (Ralph Valentino)]

The most reliable way to tell what type of drive you have is to call
the manufacturer with the model number and ask.  There is an extensive
list of phone numbers in the References section of the FAQ. 

That aside, the first thing to check is the number of pins on the
drive's connector(s).  The second thing to check is the CMOS setup,
assuming, of course, that it is in a working system.

SCSI = 1 cable: 50 pins (note 1,2)
  usually set up as "not installed" in the CMOS
IDE  = 1 cable: 40 pins
  no reliable way to tell from the CMOS
RLL  = 2 cables: 34 pins & 20 pins
  always has 26 sectors per track
MFM  = 2 cables: 34 pins & 20 pins
  always has 17 sectors per track (note 3)
ESDI = 2 cables: 34 pins & 20 pins (note 4)
  usually set up as type #1 in the CMOS and auto-configured at boot time

If you've narrowed it down to RLL/MFM or ESDI but it isn't in a
working system, there's no easy way to narrow it down any further just
by looking at the drive.

note 1: The QIC-2 tape drive interface also has 50 pins
note 2: To differentiate single ended and differential SCSI, see the scsi-faq
note 3: Some people attempt to set up MFM drives as RLL with varying success,
        this method will only tell you what it is set up as.
note 4: While ESDI uses the same type of cables as RLL and MFM, the
        signals are very different - do not connect ESDI to RLL or MFM!


Q) 3.3  Do caching controllers really help?
[From: backbone!wayne@tower.tssi.com (Wayne Schlitt)]

The short answer, is that if you are using a multi-tasking
operating system with a good memory manager, caching controllers
should be ignored.  If you are running DOS or Windows, then *maybe*
they will help, but I am not sure that they are a good buy.  

There are lots of people who have said "I put a caching controller in
my computer, and it runs faster!".  This is probably true, but they
never have measured the speed increase compared to putting the same
memory into main memory instead.  More importantly, the caching
controllers cost more money than non caching controllers, so you
should be able to add _more_ main memory instead of buying a caching
controller.

The following is a shortened up version of a much longer article.  If
you want a copy of the longer article, send me email at
"wayne@cse.unl.edu".

*** Why a multi-tasking operating system?

A multi-tasking operating system can allow the application to continue
immediately after it does a write, and the actual disk write can
happen later.  This is known as write behind.  The operating system
can also read several blocks from the file when the application
requests just part of the first block.  This is known as read ahead.
When the application requests the block later on, the block will
already be there and the OS can then schedule some more reads.

A multitasking operating system is required because these operations
can cause interrupts and processing when control has been given back to
the application.  

Basically, operating systems such as DOS, MS-Windows, MacOS and such
do not allow true preemptive multitasking and can not do the read a
heads and the write behinds.  For these systems, the latency of a disk
drive is the most important thing.  The application does not regain
control until the read or write has finished. 

*** The controller can't speed up the disk.

Remember, the bottleneck is at the disk.  Nothing that the controller
can do can make the data come off the platters any faster.  All but the
oldest and slowest controllers can keep up with all but the newest and
fastest disks.  The SCSI bus is designed to be able to keep *several*
disks busy without slowing things down.

Speeding up parts of the system that are not the bottleneck won't help
much.  The goal has to be to reduce the number of real disk accesses.

*** First, isn't the caching controller hardware and isn't hardware
*** always faster than software?

Well, yes there is a piece of physical hardware that is called the
caching controller, but no, the cache is not really "in hardware".
Managing a disk is a fairly complicated task, complicated enough that
you really can't implement the controller in combinatorial logic. 

So, just about all disk controllers and for that matter all disk
drives have a general purpose computer on them.  They run a little
software program that manages the communication between the main cpu
and the disk bus, or the disk bus and the disk.  Often this cpu is put
in with a bunch of other logic as part of a standard cell custom chip,
so you might not see a chip that says "Z80" or such.

So, we are really not comparing "hardware" with "software", we are
comparing "software on the controller" with "software on the main
cpu".

*** Ok, why can the OS win?

Assume that you have a bunch of memory that you can either put into
main memory and have the OS manage the cache, or put on a caching
controller.  Which one will be better?  Let us look at the various
cases. 

For a cache hit you have:

If the OS does the caching, you just have the OS's cache checking
latency.

If the card does the caching, you will have the OS's cache checking
latency, plus the I/O setup time, plus the controller's cache checking
latency, plus you have to move the data from the card to main memory.
If the controller does DMA, it will be taking away from the memory
bandwidth that the main CPU needs.  If the controller doesn't have
DMA, then the main CPU will have to do all the transfers, one word at
a time.

For a cache miss, you have:

If the OS does the caching, you have the OS's cache checking latency
plus the set up time for the disk I/O, plus the time it takes for the
disk to transfer the data (this will be a majority of the time), plus the
cost of doing either the DMA or having the CPU move the data into main
memory. 

The caching controller will have all of the above times, plus it's own
cache checking latency.

As you can see, the caching controller adds a lot of overhead no
matter what.  This overhead can only be offset when you get a cache
hit, but since you have the same amount of memory on the controller
and the main cpu, you should have the same number of cache hits in
either case.  Therefore, the caching controller will always give more
overhead than an OS managed cache.

*** Yeah, but there is this processor on the controller doing the
*** cache checks, so you really have a multi-processor system.
*** Shouldn't this be faster than a single processor?  Doesn't this
*** allow the main cpu to do other things while the controller manages
*** the cache?

Yes, this really is a multi-processor system, but multi-processors are
not always faster than uni-processors.  In particular, multi-processor
systems have communication overhead.  In this case, you are
communicating with the controller using a protocol that is fairly
expensive, with outb instructions and interrupts and such.  The
overhead of communicating with this other processor is greater than
the overhead of just checking the cache on main cpu, even if the main
cpu is very slow.  

The multi-processor aspect just doesn't help out when you are talking
about managing a cache.  There is just too much communication overhead
and too little processing for it to be a win.

*** Ok, but couldn't the caching controller do a better job of
*** managing the cache?

Both the controller and the OS are going to be executing a piece of
software, so in theory there isn't anything that the slower cpu on the
controller can do that the OS can't do, but the OS can do things that
the controller can't do.

Here are some of the things that the OS can do better:

* When you read a block from a file, the OS can read several more
  blocks ahead of time.  Caching controllers often will read an entire
  track in order to simulate this file read a head, but the rest of
  the file isn't always on the same track, only the OS knows where the
  blocks are really going to be at.  This can lead to wasted time and
  cache memory reading data that will never be used.

* In order to improve file system reliability, some writes _must_
  complete immediately, and _must_ complete in the order that they are
  given.  Otherwise, the file system structures may not be left in a
  coherent state if the system crashes.

  Other writes can be completed as time is available, and can be done
  in any order.  The operating system knows the difference between
  these cases and can do the writes appropriately.

  Caching controllers, on the other hand, don't know if the write that
  it was just given _must_ be written right away, or if it can wait a
  little bit.  If it waits when it shouldn't, you are risking your
  file system and data.  

* Sometimes, you want a large disk cache if you are accessing lots of
  data off the disk.  At other times, you want a small disk cache and
  more memory left to programs.  The operating system can balance
  these needs dynamically and adjust the amount of disk cache
  automatically.

  If you put the memory on a caching controller, then that memory can
  _only_ be used for disk caches, and you can _never_ use more.
  Chances are, you will either have too much or too little memory
  dedicated to the cache at any give time. 

* When a process closes a file, the operating system knows that the
  blocks associated with that file are not as likely to to be used
  again as those blocks associated with files that are still open.
  Only the operating system is going to know when files are closed,
  the controller won't.  Similar things happen with processes.

* In the area of Virtual Memory, the OS does an extremely better job
  of managing things.  When a program accesses a piece of memory, the
  CPU will do a hardware level check to see if the page is in memory.
  If the page is in memory, then there will basically be no delay.  It
  is only when the page isn't in memory that the OS gets involved.

  Even if all of those extra pages are sitting in the
  caching controller's memory, they still have to be moved to main
  memory with all the overhead that that involves.

  This is why dynamic caches vs program memory is so important.

*** What is the "Memory Hierarchy" and how does this relate to
*** caching controllers?

The basic idea of a memory hierarchy is to layer various types of
memory, so that the fastest memory is closest to the cpu.  Faster
memory is more expensive, so you can't use only the fastest type and
still be cheap.  If a piece of data isn't in the highest (fastest)
level of the hierarchy, then you have to check the next level down.

In order for a memory hierarchy to work well, you need to make sure
that the each level of the hierarchy has much more storage then the
level above it, otherwise you wont have a high hit rate.

The hierarchy on a 486 goes something like this:

8 regs << 8k on chip cache << 256k off chip cache << main memory << disk

If you are going to put something between main memory and disk, it
needs to be much larger than main memory in order for it to be
effective. 

*** What about all these neat things that a caching controller can do
*** such as elevator seeking, overlapping seeks with reads and writes,
*** scatter/gather, etc...

These are nice features, but they are all done by either the OS or a
good SCSI controller anyway.  None of these things are at all related
to supporting the cache, so you shouldn't buy a caching controller for
just these features.

*** Ok, you have talked about things like Unix, OS/2 and Windows NT,
*** but what about DOS and MS-Windows?

Well, here things get a lot grayer.  First, older versions of DOS have
notoriously bad disk cache programs.  Since neither DOS nor MS-Windows
are preemptive multi-tasking systems, it is much harder to do read
ahead.  Also, since DOS/MS-Windows users are used to being able to
power off their computers at any time, doing write behind is much more
dangerous.  DOS and MS-Windows also can crash much easier than these
other OS's, so people might reboot for many reasons.

Caching controllers usually leave the hard disk light on when they
have data that hasn't been written out, and people don't usually power
their computer off until that light goes out.  This lets the
controllers do write behind fairly safely.  (But you can still loose
power, so this isn't risk free.)  They also do crude read a heads by
prereading entire tracks.

DOS also runs in real mode and real mode can only access 640K of
memory.  This mean that a disk cache can be real helpful.
Unfortunately, to do a software based disk cache, the cpu has to be
switched into protected mode in order to access memory beyond the 640K
boundary and then you have to switch back into real mode.  Intel,
however forgot to make it easy to switch back to real mode.   All in
all, this switching back and forth ends up being real expensive.  This
_might_ be more expensive than just using a caching controller, I
don't know.

So, it is possible that if you configure DOS to not use a cache, and
get a caching controller, then you might be a head.  I really don't
know much about this area.  I have not done any real timings of this.

*** So, when would you ever want to buy a caching controller?

The answer is not too often, but there are a few cases that I can
think of:

* You have filled up all your SIMM slots on your motherboard and in
  order to add more memory you would have to throw some out.  This is
  a real shaky reason.  You can always sell your old memory, or move
  it to another computer.  The jump from 4 1MB SIMMs to 4 4MB SIMMs is
  large, but you will be much better off in the long run with more
  main memory.

* You have maxed out your memory and you need it all for programs and
  data.  If you can't put any more memory on the mother board, then
  you don't have many choices.

* If you have a bunch of slow (100ns-120ns) memory left over from say
  a 286 or something and you can't use it on your motherboard because
  it is too slow, then maybe adding it to a caching controller
  will help.  Be careful however, if your hit rates on the caching
  controller are too low, then you may be just adding overhead without
  getting any benefits.

* If you are stuck with a bad OS because that's what your applications
  run on, then you might be better off with a caching controller.

*** What about those disk drives that come with caches, are they bad too?

Don't confuse caching disk controllers with cache on disk drives.  The
latter is actually useful.  The little cpu on the disk drive has to
read every byte that comes off the disk in order to see when the
sector that you are interested in has come under the heads and to do
any error detection and correction.  The disk also has to have buffers
in case the bus is busy, and to sync up the speeds of the bus and the
heads.

Since all this data is going though the cpu on disk drive and you have
to have a buffer anyway, just making the buffer larger and saving the
entire track is an easy win.  Saving a couple of the most frequent
tracks is also a win.

Most of these caches on the disk drives are fairly small (64k-256k),
and a single memory chip will give you about that amount of memory
anyway, so you aren't wasting many resources.  This also allows the OS
to always assume that interleaving is not necessary to get full disk
throughput, even if it does a fair amount of processing between disk
requests. 

Q) 3.4  Do IDE controllers use DMA?

No, they do not.  This is a rumor that keeps popping up.  This may
change on the next revision of the standard.

Q) 3.5  Why won't my two IDE drives work together?

[From: jruchak@mtmis1.mis.semi.harris.com (John Anthony Ruchak)]

Assuming that the drives are attached to the same controller and they
work properly when attached one-at-a-time, you probably don't have
them configured properly for Master/Slave operation.

When operating 2 IDE drives, one must be designated as "Master" and
the other as "Slave."  There are jumpers on every IDE drive to
configure this.  Check your hard drive manuals for the jumper settings
for your drives.  In general, it doesn't matter which is which - just
pick one as master, and make the other slave.

In your CMOS configuration, Drive 1 should have the parameters (heads,
cylinders, etc.) that match the drive you set as "Master" and Drive
2's parameters should match those of the "slave" drive.  In operation,
the Master will appear as drive C: and the slave as drive D:.

Because not all hard drive manufacturers follow the IDE specifications
closely enough, drives from 2 different manufacturers may not work well
together.  In this case, changing master -> slave and slave -> master
(along with the appropriate CMOS changes) may help.  If it doesn't,
then trying two drives from the SAME manufacturer is the only avenue
you have left.

Q) 3.6  Which is better, VLB or ISA IDE?
[From: pieterh@sci.kun.nl]

If a simple answer is what you want, then yes, in general VLB IDE
controllers are better than ISA ones.  If you are purchasing or
putting together a computer, the relatively small price difference
makes the choice for a VLB controller a sensible one.

However, if you already have an ISA controller and are wondering
whether it's worth upgrading to VLB, it's not that easy.  VLB may be
faster in principle, the question is if you're going to notice it.


 *** The Bottlenecks

Let's take a look at what the limiting factors are in the path the
data travels from your drive platter to the CPU.

1. Raw data transfer from the drive platter.  To find out what this
   rate is, you need the spec sheet for your drive.  Remember that
   it is dependent on the cylinder, so a single drive can give
   different results depending on where on the drive you're testing.
   
   Anyway, this transfer rate is 1 to 2 MB/s on most IDE drives,
   depending on data density and rotational speed.

2. The data has to be digested by the drive's onboard controller,
   which not only mediates between the drive hardware and the IDE
   bus, but also manages the buffer cache.  Let's hope it's both
   fast and intelligent (not always the case *sigh*).
   
3. Data transfer over the IDE/ATA bus (2-3MB/s with standard
   timing).  The actual speed depends on the timing used; some
   drives and controllers support faster timing.  Enhanced IDE
   (IDE-2) can transfer up to 11 MB/s.
 
4. Transfer from the interface to the CPU (ISA: max 5 Mb/s, VLB:
   10-80 MB/s depending on CPU clock, wait states, interface...)
 
A generic IDE interface is usually not able to get the most out
of the ISA and IDE bandwidths (3 and 4); a typical upper limit is
about 2 MB/s if you use block transfers (see below), 2.5 MB/s if
you're willing to push the ISA bus clock a little (more about
that later on).

Still, it's clear that on all but the fastest drives the raw data
transfer rate to/from the drive platter (1) will determine the
maximum performance you're going to get.  If you're getting
transfer rates near this limit, you can't significantly improve
your throughput whatever you do.


 *** Tuning Your Harddisk

Suppose your harddisk throughput is lower than you think is
possible with your drive.  How can you tune your system to improve
hard disk performance?  I'll go through points 1-4 again and
indicate what you can do to widen up the bottlenecks a little.

1. Drive platter to head transfer.
    - Sorry, there's nothing you can do short of getting a new
      drive.
      
2. The drive controller.
    - Many modern drives understand "block transfer", also known as
      multi-sector I/O or read/write multiple.  Although the newest
      BIOSes have this feature built in, most of us will have to
      use a driver.  More about that at the end of this section.
      
      What is block transfer?  Normally, for each sector the
      computer wants to read from or write to the drive, it has to
      issue a separate command.  When you're transfering 2 MB/s,
      that means you're sending the drive 4,000 commands each
      second.  Each command has to be issued by the CPU, transferred
      over the ISA and IDE buses, interpreted and acted upon by the
      drive's onboard controller.  Every such command takes a little
      time.
   
      By using block transfer mode, it is possible to read or write
      more than one sector (usually 4 to 32) using a single command.
      This greatly cuts down command overhead, as you can imagine,
      and may very well have a dramatic effect on a badly performing
      system.  In most cases, it will improve performance by 5-20%.
      
      Unfortunately some older drives have inferior support of this
      feature and actually slow down...  or in exceptional cases
      even hose your data.

3. The IDE bus.
    - With most drives you can use faster IDE bus timing, but your
      interface has to support this.  Modern IDE interface chips
      often have completely programmable timing; these can be
      exceptionally fast if the software supports this feature and,
      of course, if the drive can keep up.  Some controllers use
      jumpers to configure timing.

      The last word in IDE bus bandwidth is of course the Enhanced
      IDE bus, which allows exceedingly fast transfers if both
      drives and interface support it.

      If you cannot use improved timing with a new VLB interface,
      the IDE bus will prove to be as much as a bottleneck as the
      ISA bus was.

    - Not all interfaces are created equal, some are better
      engineered.  With the current VLB hype, there's bound to be
      a friend who has an old (ISA) interface gathering dust; try
      that one.

4. The ISA bus.
    - The official speed of the ISA bus is about 8 MHz, but most
      cards, especially modern ones, will work fine on 11 MHz or
      more (some will even take as much as 20 MHz).  If you don't
      mind experimenting, it may be worthwhile to see if your
      ISA cards run reliably at a higher bus clock.  This is
      especially interesting if your drive nears the 2MB/s mark.

      The BIOS setup has to support this, of course.

      *WARNING* Pushing the ISA bus clock beyond spec often works
      well, but there is always the risk that it DESTROYS YOUR
      DATA.  Make a backup before attempting this and thoroughly
      verify correct operation before entrusting critical jobs to
      a "pushed" system.

    - Finally, if you need more than the 2.5-3 MB/s or so you can
      squeeze out of a good ISA controller, VLB is the way to go.
      Be aware that the controllers on the market are of variable
      quality; VLB alone isn't going to be enough if you need the
      highest performance.  It has occurred that a VLB interface
      proved to be, all things equal, slower than the ISA one it
      replaced!

      Take special note of the drivers: they must be stable and
      support whatever software you intend to use (DOS, Windows
      32-bit VxD, OS/2).  Without a driver loaded, the VLB
      interface will perform no better than an ISA controller.

A final word about block transfer drivers.  VLB controllers are
usually shipped with a TSR that, among other things, enables block
transfers (usually designated "Turbo" mode)---this is often where
most of the performance gain actually comes from.  But block mode
is equally possible using ISA based interfaces.  Popular block
transfer drivers are Drive Rocket and DiskQwik.  You can get a
crippled version of the latter from Simtel:

        pub/msdos/diskutil/dqwik110.zip

If you're using Linux, you can use Mark Lord's IDE performance
patches to enable block mode.  In true multitasking operating
systems, block transfers have the additional advantage of greatly
reducing CPU load.


Q) 3.7  How do I install a second controller?
[From: strople@ug.cs.dal.ca (PAUL LESLIE STROPLE)]

The following should solve about 95% (9.5?) of second controller
problems, if only to tell you it can't be done!
 
Generic Second Controller Installation:

1) Normally the MFM/IDE/RLL controller is set up as the primary, and
the ESDI/SCSI as the secondary; One reason for this is because the
ESDI/SCSI controller cards are usually more flexible in their set up
and secondly this method seems to work (probably due to reason one).
 
2) Your primary controller is set up using all the normal defaults:
   - Floppy  at primary address(3F0-3F7).
   - Hard disk enabled, at primary addresses (1F0-1F7),
BIOS address C800 and interrupt 14.
 
3) Your secondary controller is set up as:
   - Floppy drives disabled
   - Hard disk controller enabled, secondary address(170- 177) and
     interrupt 15.
   - NOTE: onboard bios set to D400, or D800 can be used, if there is a
     conflict.
 
4) Computer BIOS Setup:
   - Any drive(s) on the primary controller (MFM/IDE), should be
     entered in the BIOS setup as usual.
   - You DO NOT enter the drive types for the hard disks on the
secondary controller, even if there are only two drives in the entire
system i.e., if one drive on each controller you only enter the drive
type of the hard disk on the primary controller -- the 2nd drive type
is left as not installed (0).
 
Operating System:
 
If you do the above steps you now have the hardware setup correctly;
your only other problem may be with the operating system.
 
Different OSs handle secondary controllers differently; as well,
different controllers handles same OSs differently (scared yet?).
 
For example: with DOS you may require a device driver (available from
the manufacture or through third party companies, such as Ontrack
Computer Systems -- more on Ontrack later). Some flavors of UNIX
handle a mixture of controllers better than others (e.g., IA 5.4 had
probs mixing ESDI and SCSI controllers under certain conditions).
 
Procedure:
 
You should verify that your secondary controller, and associated hard
drives, are working properly (you can try this by installing it as the
primary system -- removing existing system first!).  Follow above
steps 1 to 4, pray, and turn on system! If it still won't work you may
need additional drivers. First check with the supplier or manufacture
(I know, for example, a DTC ESDI controller comes with the DOS drivers
included, and it works perfectly).
 
I am not sure of operating systems supported by Ontrack Data Systems.
I know that their DOS driver can assist secondary controllers, even
allowing two IDEs to co-exist. Likewise, the drivers can also install
virtually any drive, regardless of what is supported by the BIOS.
 
BIG NOTE: The features required in a secondary controller are normally
not found on a $30.00 IDE controller. The best thing to do it, if
possible, is to get a guarantee from the supplier/manufacture that if
it doesn't work (and they can't make it) then they will take it back.
 
Ontrack supplies a complete range of hard disk products and services
-- from driver software, data recovery services, to media and data
conversions (including tape backups).  The product I know them from is
DiskManager.
 
Disk Manager is a utility for hard disk management. It will allow you
to setup and install virtually any hard disk, regardless of disk's
layout and BIOS options available. Disk Manager (version greater than
5.2.X, or there abouts) includes a driver for co-resident controllers.
For driver to work the co-res board must be able to hit the above
addresses and must be WD1003 AT command set compatible (this includes
most IDE and ESDI boards).
 
DM contains a number of features, including full diagnostics.  You may
not need to know the disk's geometry, as there are numerous layouts
stored internally. All you need to do is select the correct model and
DM does the rest.
 
To contact Ontrack: U.S.  (800)-872-2599; UK 0800-24 39 96 this is
either an address or phone number! outside U.K. (but NOT U.S.)
44-81-974 5522

Q) 3.8  >What is EIDE/Fast-ATA/ATA-2/ATAPI what advantages do they have?

This topic is posted separately as the "Enhanced IDE/Fast-ATA/ATA-2 FAQ"
and archived along side this FAQ.  Refer to section one for
instructions on retrieving this file.

Newsgroups: comp.sys.ibm.pc.hardware.storage,comp.sys.ibm.pc.hardware.misc,
            comp.answers,news.answers
Subject: Enhanced IDE/Fast-ATA/ATA-2 FAQ [* of *]
From: pieterh@sci.kun.nl (Maintainer)
Summary: This FAQ addresses issues surrounding Enhanced IDE, ATA-2,
    ATAPI and Enhanced BIOSes. It includes practical questions,
    background information and lists of net resources.
Archive-name: pc-hardware-faq/enhanced-IDE


Q) 3.9  Which is better, SCSI or IDE?
[From: ralf@wpi.wpi.edu (Ralph Valentino)]

IDE vs SCSI

Non-issues:
1) SCSI and IDE devices cost approximately the same for the same
   features (size, speed, access time).  Shop around for good prices.

Advantages of IDE:
1) faster response time (low request overhead)
2) hard drive interface is compatible with RLL/MFM/ESDI: any driver
for one (including the main system BIOS) will run the other.
3) IDE controllers are considerably cheaper ($150 and up) than SCSI
   host adapters. 
4) Will always be the boot device when mixed with SCSI.

Advantages of SCSI:
1) Supports up to 7 devices per host adapter.  This saves slots,
IRQ's, DMA channels and, as you add devices, money.
2) Supports different types of devices simultaneously the same host
adapter (hard drives, tape drives, CDROMs, scanners, etc).
3) SCSI devices will work in other systems as well (Mac, Sparc, and
countless other workstations and mainframes).  If you change platforms
in the future, you will still be able to use your SCSI devices.
4) Automatically configures device type, geometry (size), speed and
even manufacturer/model number(SCSI-2).  No need to look up CMOS
settings.
5) Busmastering DMA (available in all but a few cheap SCSI host
adapters) decreases amount of CPU time required to do I/O, leaving
more time to work on other tasks (in multitasking OS's only).
6) Software portability - drivers are written for the host adapter,
not the specific device.  That is, if you have a CDROM driver for your
host adapter, you can purchase any brand or speed SCSI CDROM drive and
it will work in your system.
7) Will coexist with any other type of controller (IDE/RLL/MFM/ESDI)
or host adapter (other SCSI cards) without any special tricks.  SCSI
host adapters do not take up one of the two available hard drive
controller port addresses.
8) greater bandwidth utilization (higher throughput) with multiple
devices.  Supports pending requests, which allows the system to
overlap requests to multiple devices so that one device can be seeking
while the second is returning data.
9) Ability to "share" devices between machines by connecting them to
the same SCSI bus.  (note: this is considerably more difficult to do
than it sounds).
10) Bridges are available to hook RLL and ESDI drives to your SCSI host
adapter.  (note: these tend to be prohibitively expensive, though).

Warnings:
1) With otherwise equal drives, IDE will perform better in DOS due to
low command overhead.  SCSI, however, will perform better in
multitasking OS's (OS/2, Unix, NT, etc).  If you see speed comparisons
(benchmarks), make sure you know what OS they were run under.
2) Most benchmarks only test one aspect of your system at a time, not
the effect various aspects have on each other.  For instance, an IDE
drive may get faster throughput but hurt CPU performance during the
transfer, so your system may actually run slower.  Similar confusions
arise when comparing VLB and EISA host adapters.
3) When comparing two systems, keep in mind that CPU, memory, cache,
and bus speed/type will all effect disk performance.  If someone gets
great I/O performance with a particular controller/drive combination
on his Pentium, you should not expect your 386SX-25 to get such I/O
performance even with the exact same controller/drive combination.
4) Similarly sized or even priced drives may not perform equally, even
if they're made by the same manufacturer.  If you're going to compare
two drives, make sure they have the exact same model number.  (IDE
drives usually have an 'A' and SCSI drives usually have an 'S'
appended to their model number).

Q) 3.10  Can MFM/RLL/ESDI/IDE and SCSI coexist?

The PC is limited to two drive controllers total.  SCSI, however, is a
"host adapter" and not a drive controller.  To the rest of your
system, it appears more like an ethernet card than a drive controller.
For this reason, SCSI will always be able to coexist with any type
drive controller.  The main drawback here is that on most systems, you
must boot off a disk on the primary drive controller, if you have one.
That means if you have SCSI and IDE in your system, for example, you
can not directly boot from the SCSI drive.  There are various ways to
get around this limitation, including the use of a boot manager.

Q) 3.11  What's the difference between SCSI and SCSI-2? Are they compatible?

The main difference between SCSI and SCSI-2 are some new minor
features that the average person will never notice.  Both run at a
maximum 5M/s.  (note: Fast and Wide SCSI-2 will potentially run at
faster rates).  All versions of SCSI will work together.  On power up,
the SCSI host adapter and each device (separately) determine the best
command set the speed that each is capable of.  For more information
on this, refer to the comp.periphs.scsi FAQ.

Q) 3.12  How am I suppose to terminate the SCSI bus?

Some basic rules on termination:

1. The SCSI bus needs exactly two terminators, never more, never less. 
2. Devices on the SCSI bus should form a single chain that can be
   traced from the device at one end to the device at the other.  No
   'T's are allowed; stub length should be kept as short as possible.
3. The device at each end of the (physical) SCSI bus must be
   terminated, all other devices must be unterminated.
4. All unused connectors must be placed _between_ the two terminated devices.
5. The host adapter (controller) is a SCSI device.
6. Host adapters may have both an internal and external connector; these
   are tied together internally and should be thought of as an "in"
   and "out" (though direction has no real meaning).  If you have only
   internal or external devices, the host adapter is terminated
   otherwise it is not.
7. SCSI ID's are logical assignments and have nothing to do with where
   they go on the SCSI bus or if they should be terminated.
8. Just because your incorrectly terminated system happens to work
   now, don't count on it continuing to do so.  Fix the termination.

Examples:

      internal      external           internal            external
    T------|-----|------T          T------|-------|-----|------|------T
 drive   drive   HA    cdrom      tape  unused unused   HA   drive  drive

        internal             external             external
     T------|-----T      T------|------T          T------T
   drive  drive   HA     HA    tape   cdrom       HA    cdrom

"T" = terminator   "|" = connector (no terminator)   "HA" = Host Adapter

Q) 3.13  Can I share SCSI devices between computers?

There are two ways to share SCSI devices.  The first is removing the
device from one SCSI host adapter and placing it on a second.  This
will always work if the power is off and will usually work with the
power on, but for it to be guaranteed to work with the power on, your
host adapter must be able to support "hot swaps" - the ability to
recover from any errors the removal/addition might cause on the SCSI
bus.  This ability is most common in RAID systems.

The second way to share SCSI devices is by connecting two SCSI busses
together.  This is theoretically possible, but difficult in practice,
especially when disk drives are on the same SCSI chain.  There are a
number of resource reservation issues which must be resolved in the
OS, including disk caching.  Don't expect it to 'just work'.

Q) 3.14  What is Thermal Recalibration?

When the temperature of the hard drive changes, the media expands
slightly.  In modern drives, the data is so densely packed that this
expansion can actually become significant, and if it is not taken into
account, data written when the drive is cold may not be able to be
read when the drive is warm.  To compensate for this, many drives now
perform "Thermal Recalibration" every degree C (or so) as the drive
warms up and then some longer periodic interval once the drive has
reached normal operating temperature.  When thermal recalibration
takes place, the heads are moved and the drive may sound like you are
accessing it.  This is perfectly normal.

If you're attempting to access the drive when thermal recalibration
occurs, you may experience a slight delay.  The only time this becomes
important is when you're doing real-time operations like recording /
playing sound or video.  Proper software buffering of the data should
be able to hide this from the application, but software seldom does
the proper thing on its own.  Because of this, a few companies have
come out with special drive models for audio/video use which employ
special buffering techniques right on the drive.  These drives, of
course, cost significantly more than their counterparts.  Some other
drives offer a way to trigger thermal recalibration prematurely (thus
resetting the timer), so if your real-time operation is shorter than
the recalibration interval, you can use this to assure your operation
goes uninterrupted.  Disabling or delaying recalibration is dangerous
and should be completely avoided.  For more information on the thermal
recalibration characteristics of a drive, contact the drive
manufacturer directly.

Q) 3.15  Can I mount my hard drive sideways/upside down?

Old hard drives always had specific requirements for mounting while
most modern hard drives can be mounted in any orientation.  Some
modern hard drives still have mounting restrictions; the only way to
be sure is to read the documentation that comes with the drive or
contact the manufacturer directly and ask.  Restrictions may be model
specific so be sure you know the exact model number of your drive.  A
common misconception is that it is always safe to mount the circuit
board side up, this is not the case.  When in doubt, look it up.

Failure to follow the mounting instructions can result in a shortened
lifetime.


Q) 3.16  How do I swap A: and B:
[From: rgeens@wins.uia.ac.be (Ronald Geens)]

To swap A: and B: drives :
1) open up your machine to see if look at the cable that interconnects
the 2 drives.
2) if the cable is twisted, there is no problem, just switch the
connectors from 1 drive to the other.And change the bios-setup.
3) if the cable isn't twisted (which is very,very rare), it's a little
harder: leave the cables as they are, but change the jumpers on the
drive. (this sounds a lot tougher, but it can usually be done without
to much hassle.  When the cable connecting the 2 drives is just a flat
one (like the harddisk cable) then you must play with the jumpers on
the drives: Most of the time, there is a jumper with 4 pins, with the
following layout:
                               _
                              |1|
                             |2*3|
                              ---

Where the * is the 4th unnumbered pin. Normally the A: drive will have a 
jumper on pin 2 & 4 and the B: drive on 1 & 4. Just change these jumpers 
around, (i.e. new A: 2&4, new B: 1&4) and change the BIOS configuration.
4) Don't panic if it doesn't work, just make sure all cables are
conected properly and if that doesn't work just restore everything to
its old state.
PS. By twisted cable, I mean that between the A: and B: drive, a few
wires of the flat cable are turned around.

[From: sward+@CMU.EDU (David Reeve Sward)]

I have found two ways to do this: I originally switched their
positions on the cable attached to the controller, and changed the
BIOS to reflect this.  I recently got a gsi model 21 controller for my
IDE drive, and this controller allows you to specify which drive is A:
and B: in software (it lights the LEDs in turn and asks which is A:
and which is B:).  This did not require a cable change (but I still
changed by BIOS).

Q) 3.17  My floppy drive doesn't work and the light remains on, why?

If you've played around with the floppy cables at all, chances are you
put one of them on backwards.  In general, floppy cables aren't keyed
to prevent this.  Carefully find pin 1 on all floppy drives and the
floppy controller and make sure they all line up with pin 1 on the
cable.  If you have trouble with this, "How do I find pin 1..."
elsewhere in this FAQ may be of some help.

Q) 3.18  What is a 16550 and do I need one?

The 16550 is a UART with two 16 byte FIFOs.  A UART is the part of a
serial port that takes byte-wide (characters) data and converts it to
bit-wide (serial) data, and visa versa.  The FIFO is a buffer which
can hold characters until the CPU is ready to remove it or until the
serial line is ready to transmit it.  The 'normal' UART in the PC (the
8250 or 16450) only has 1-byte FIFOs.  The additional 15 bytes can be
useful when the CPU is busy doing other things - if the CPU isn't able
to remove data fast enough, it will be lost.  The OS or program has to
explicitly support 16550 to make full use of its advantages.

A very important thing to note is that under DOS, the CPU doesn't have
anything else to do, so the 16550 is wasted.  Only under multitasking
operating systems does it really become useful.  The 16550 will *not*
make your file transfers any faster, it will only prevent data from
being lost and relieve your CPU of some overhead.  If you notice
system performance dropping like a rock when file transfers are
occurring, a 16550 may be helpful.  If you see re-transmissions (bad
packets) or "FIFO overrun's" during file transfers under a
multitasking OS, try the same thing under DOS - if the errors go away,
then chances are a 16550 will be useful.  If they remain, then your
problem is likely to be elsewhere.

Q) 3.19  Are there any >4 channel serial port cards?
[From: wkg@netcom.com (William K. Groll)]

Here is a partial listing of vendors or serial port cards with greater
than 4 ports.  In almost all cases cables and/or interface panels are
required to make the physical connection to the phone lines. Some of
these interfaces can be almost as expensive as the cards themselves,
so find out what is needed before you order. Prices, if available in
their current (late '94 or early '95 issue) catalog/price-list, are
given below and do not include cables, connector panels, etc. unless
noted. Some also offer driver software, either included with the card
or at additional cost. Some of the cards have an on-board processor to
handle the communications, while other lower cost boards require the
main CPU to perform all of the housekeeping chores.

These are primarily manufacturers/distributors of industrial PCs for
embedded applications, but they will sell mail-order in single
quantities. I have not personally used _any_ of these cards, but
believe the vendors to be reputable businesses. They offer warranties
and some technical support, but as always ask before you buy and
"caveat emptor".

Another source for information on this type of card is manufacturers
of BBS software.


Advantech (408)245-6678, fax 245-8268
    PCL-844, 8-port Intelligent RS-232 Card

Axiom (909)464-1881, fax 464-1882
    C218, Intelligent 8-port Async Card; 
    C216, 16-port Intelligent RS-232 Interface Card

Contec (800)888-8884, fax (408)434-6884
    COM-8SF(PC), Intelligent RS-232 Interface with 8 ports 
    (up to 4 boards/system): $495

CyberResearch (800)341-2525, fax (203)483-9024
    many models from 4 to 32 ports, $359 to $2895 
    (appears to include cost of connectors)

Industrial Computer Source (800)523-2320, fax (619)677-0898
    many models from 4 to 32 ports, $399 to $1099

Personal Computing Tools (800)767-6728, fax (617)740-2728
    various 4, 8, and 16-port cards, $299 to $999

QuaTech (800)553-1170, fax 434-1409
    various models with 4 or 8 ports, $299 to $675

Sealevel Systems (803)843-4343, fax 843-3067
    3420, 8-port RS-232 card: $499 (includes cable with connectors)


Q) 3.20  Should I buy an internal or external modem?
[From: arnoud@ijssel.hacktic.nl (Arnoud Martens)]

While low speed modems are often only produced as an internal PC card,
most modem manufacturers provide two versions of their higher speed
modems:

1: internal ISA bus card, specially designed to work with the
standard PC bus. You just plug it in and configure it to use on
port.

2: external modem that has to be connected to the serial ports of
your PC (com 1-4), using a serial RS232 cable.

In most cases the functionality of these two is equal. There are
however some differences in using, maintaining and buying these
modems. It is very difficult to give an definite answer as to which one
is better, it completely depends on your own situation. Some of the
points that are in favor of an external modem are:

  * It has lights showing the status of the connection, this can be
    useful in those (rare) cases that you have problems with the
    connection.

  * It can be used on a wide range of systems. External modems
    are connected using a RS232 cable, a standard that most computer
    systems support. So you can as easily use your external modem
    on a Mac, Amiga or Unix box as on your PC. 

  * It doesn't consume power inside the PC (it uses a normal net
    adapter), and doesn't produce any heat inside your PC.

On the other hand the internal modem has also a couple of advantages
compared to an external modem:
   
  * It is always cheaper, Somewhere in the order of 10% less compared
    to the same external modem.

  * It doesn't need special serial hardware since it has already
    been integrated on the board, which will make it even more
    cheaper. 
   
So basically if portability of your modem is an issue, you are better
of with an external modem. But if you only intend to use the modem
with your PC and don't have any power problems, an internal modem is
the best choice.

Q) 3.21  What do all of the modem terms mean?
[From: arnoud@ijssel.hacktic.nl (Arnoud Martens)]

A modem (MOdulator-DEModulator) is a device capable of converting digital
data from your computer into an analog signal that is suitable for
transmission over low band width telephone lines. A modem thus makes it
possible to connect two computers over a telephone line and exchange data
between them.

Basically a modem picks up the phone, and dails a number. A modem on
the other side will pick up the phone and the two modems will
negotiate which protocol to use. When they agree the actual
transmission of data can begin.

The major feature of a modem is the speed that it can achieve
connecting to other modems. This speed is often expressed in baud or
bits per second. The first is a feature of the line and specifies how
much of the bandwidth of the phone channel is used and is fixed to
2400 baud. A baud is defined as the number of lines changes per
second. Bits per second is the actual amount of data transmitted in
one second. Most modems are capable of sending more than one bit per
line transition by using very intelligent signal modulation
techniques. So the bps can be eight times higher compared to trhe baud
rate.

The modulation techniques that a modem uses are standarized by the
ITU-T ( former CCITT), so that modems of different brands can connect
to each other as they use the same modulation schemes. These standards
are often incorporated in a protocol definition that is referred to by
the letter V followed by a number. The most common protocols are:

    V21: (300 baud)
    V22bis: (2400 baud)
    V32: (9600 baud)  
    V32bis: (14400 baud)

A modem is often advertised only by its fastest protocol, most of these
modems "speak" slower protocols as well.

There are also standards on using data compression by the modem, such as MNP5
and V42bis, and error control protocols (V42 and MNP4). These standards can
reduce the transmitted data by a factor four, by using advanced compression
techniques. 

To give you an idea a how fast fast is in modem technology: V32bis transmits
somewhat like 1600 characters per second (that is ~33% of 1 page of
text). Transferring a file of 1Mb takes about 12 minutes. Using V42bis can
speed up transmission to 4000 characters per second for uncompressed data.

Apart from these standardized protocols there are also faster protocols which
are supported by some modem manufacturers. But remember anything faster than
14k4 is *not yet* standarized, and often different manufacturers use their
own modulation scheme that allows only their own modems communicate at that
speed. The most common high speed protocols are:

    V32 terbo (19200 baud)
    V34 (28800 baud) or Vfast. 

The standard for V34 is being worked on, it will be released somewhere in
1994. Some modem manufacturers already sell modems with the (prelimenary) V34
standard. If you are serious about buying a fast modem, upgradability to this
standard should be provided by the manufacturer.

When you use your modem it is important to differentiate between command
status and connect status of your modem. When you are connected to an another
modem everything you send to the modem, will be transmitted to the other
modem. In command mode everything you type will be recieved and interpreted
by the modem. Command mode allows you to change the default settings for
youyr modem.

In command mode it is likely that your modem will respond to the Hayes AT
command set. "AT commands" all have prefix AT, and can be used to change the
(default) settings of your modem. To check if your modem works, fire up a
terminal program (such as kermit), connect to your modem (in kermit c
[ENTER]) and issue AT [ENTER], if your modem works it should respond with
OK. For a list of all "AT commands" see the manual of your modem, as most AT
commands are modem specific.

If you buy a fax-modem, you should pay attention to a couple of things. First
the modem must support Class 2 fax commands, furthermore automatic fax mode
selection is a big pro. That means if you receive a call the modem is capable
of detecting a fax message or a modem connection and act properly (start up a
fax receiving program or spawn something like a login process on the
connection).

Finally there is no best modem to get, brands and qualities change very fast,
as do the prices. If you are interested in buying one, subscribe to the
newsgroup comp.dcom.modems, most postings in this group are very brand
oriented and you will recognize fast enough which users are satisfied over
their modems and which are not.

Q) 3.22  Why does my fast modem connect at a lower speed?

For 28.8 modems that connect at lower speeds such as 22, 24 or 26.4,
this is perfectly normal.  The usable channel capacity of the
telephone system with a ideal connection is just over 28.8k.  In
reality, you'll very rarely see a 28.8k connection so don't expect
it.  When the two modems connect, they will evaluate the connection
quality and pick a corresponding speed.  If you have your modem set up
correctly, it will retrain every once in a while and increase or
decrease your connection speed based on the current line quality.

For modems that connect at considerably lower than expected speeds
(such as 2400 for a 9600+ modem), there are two possibilities.  The
first possibility is that the remote modem can't handle the higher
speed.  There is nothing you can do about this except call a faster
modem.  The other possibility is that you have your serial port / comm
software set up incorrectly.

When you connect your PC to another machine through modems, there are
actually three connections being made: PC1 to modem1, modem1 to modem2
and modem2 to PC2.  The speed of the modem (2400,9600,14.4,28.8) is
the rate (more or less) at which the modem1 will speak to modem2.  The
PC to modem connections are based on the speed your COM port is set
to.  If you set the COM port speed to 2400, the modem to modem speed
will drop accordingly.  For this reason, you want to set the COM port
speed at least as high as the modem to modem speed.  In actuality, the
modem to modem protocol may support compression and achieve data
transfers faster than the connection speed so you want to set your COM
port higher than your modem to modem connection.  For a 28.8 modem,
set the COM port to 38.4k, 57.6k, or 115k.  While higher is always
(potentially) better, some software/operating systems have trouble
with very high COM port speeds, so start with 38.4k and see how it
goes.

Q) 3.23  >What kinds of sound cards are available?

This is covered in the comp.sys.ibm.pc.soundcard FAQ, archive name:
PCsoundcard/soundcard-faq.  Please refer to this document for more
information.

Q) 3.24  Where can I find EISA/VLB sound and IO cards?

Chances are that you won't be able to find them anywhere, and if you
do, they won't be worth the money.  Sound and IO cards have very low
bandwidth requirements, over 10 times lower than the ISA bandwidth and
over 60 times lower than the EISA bandwidth.  For this reason, there
is no advantage in placing them on the more expensive EISA/VLB cards
when the less expensive ISA will more than suffice, especially
considering than all ISA cards will work in an EISA/VLB slot.

Q) 3.25  Where can I get DOS drivers for my ethernet card?
[From: ralf@wpi.edu (Ralph Valentino)]

The first thing you need is a low level packet driver for your
ethernet card.  This driver links your card specific functions to a
common software interface allowing higher level software to read
and write to your ethernet card without knowing any of the hardware
specifics.  Ethernet cards usually come with a packet driver.  If you
didn't get one, try contacting the card manufacturer (they may have a
www/ftp site, see the references section of this FAQ).

Another option is using publicly available packet drivers.  The Crynwr
packet driver collection is free, supports a significant number of
cards and comes with sources and documentation.  You can find this
package in the "pktdrvr" subdirectory on any of the Simtel mirrors.
For instance:

   wuarchive.wustl.edu:/systems/ibmpc/simtel/pktdrvr/
   ftp.uu.net:/systems/msdos/simtel/pktdrvr/

The files of interest are:

  pktdrvr11.zip  -  executable
  pktdrvr11a.zip pktdrvr11b.zip pktdrvr11c.zip  -  sources

The included instructions explain how to install them.  The file
"software.doc" (within the zip archive) contains pointers to a number
of other useful protocol drivers, which is the next thing you need.

The protocol driver sits on top of the packet driver and implements
one of the many standard protocols (IPX, TCP/IP, etc).

IPX protocol drivers, needed for many multiplayer games, can be found
in the same "pktdrvr" directory as the Crynwr packet drivers.  Files
of interest are:

    novel.zip  - IPX protocol driver from BYU
    intelpd.zip - IPX protocol driver from Intel (newer)

Either of the above will do.

For a quick TCP/IP implementation allowing telnet and file transfers
with both Unix and other DOS machines with very little setup, try
Kermit.  You can get Kermit from the Columbia University distribution
site:

   kermit.cc.columbia.edu:systems/msdos/msvibm.zip
                                  - everything you need for DOS and more

To make a connection, type:

   set tcp/ip address *.*.*.* (where *.*.*.* is your IP address)
   set port tcp/ip *.*.*.*    (where *.*.*.* is the destination IP address)
   connect

Remember to type "set file type binary" at the Kermit prompt on both
ends if you are transfering binary files (anything but unarchived
text).  See the documentation and on-line help for time transfer
optimization as well as how to set the rest of the TCP/IP related
parameters (netmast, broadcast address, bootp server, nameserver, etc)
if you are interfacing to an existing network.

Another program of interest is NCSA Telnet.

    ftp.ncsa.uiuc.edu:PC/Telnet/tel23bin.zip - binaries
    ftp.ncsa.uiuc.edu:PC/Telnet/tel23src.zip - sources

Many commercial protocol drivers/applications are also available,
including Windows for Workgroups, PC/TCP, WIN/TCP and PC-NFS, to name
a few.  See your local software store for information on these.


Q) 3.26  How does the keyboard interface work?

[From: jhallen@world.std.com (Joseph H Allen)]

The IBM keyboard is connected to the computer through a serial interface
similar to a COM port.  When you press a key, the keyboard sends a
"scan-code" for that key to the computer.  When you release the key, the
keyboard sends a release code to the computer.  If you hold down one key and
press and release another key, the computer will receive the scan-code for
the held key and a scan and release code for the other key.  Since the
release code for the held key was not received, the computer knows that the
held key was down while the other key was pressed.  In this way, the
computer can handle the Shift, Alt and Ctrl keys (and any key could work
like a shift key, since all keys work alike).  The ROM BIOS in the computer
buffers the data from the keyboard, translates the scan-codes to ASCII and
handles the operation of the shift and lock keys.  The keyboard itself also
has a small buffer and there is hardware flow-control for preventing
overruns.  All of this seems simple and quite elegant, but by the time we
get to the AT keyboard the details of the implementation are so complicated
as to ruin an otherwise ideal keyboard.

The XT keyboard's interface almost captures the above elegance (indeed it is
the only elegant thing about the XT, IMHO).  The interface uses a 5-pin DIN
connector with these signal assignments:

     1     CLK/CTS (open-collector)
     2     RxD
     3     RESET
     4     GND
     5     +5V

When the keyboard has a byte to send to the computer, it shifts 9 bits out
to the data line (RxD) with nine clock pulses on the CLK line.  The data
format is 1 start bit, followed by 8 data bits.  The baud rate is roughly
2000 bits per second and is not precisely defined.  Once a byte is
completely transmitted, the computer holds the Clear-To-Send (CTS) line low
to prevent the keyboard from sending any more bytes until the keyboard
interrupt handler reads the current one.  Usually a simple 9-bit clearable
TTL shift register is used to receive keyboard data.  The 9th bit of the
shift register is used to drive an open-collector buffer connected to the
CTS line.  When the start-bit gets all of the way through the shift
register, it holds the CTS line low itself.  Once the CPU reads the
assembled byte, it has only to clear the shift register to release the CTS
line and allow another byte to be received.  Three TTL chips or a single PAL
can implement an entire XT keyboard interface.

The data bytes which the XT sends are also simple.  Codes 0-127 are the
scan-codes.  Codes 128-255 are the release codes- they're the same as the
scan codes, but with the high bit set.  The XT keyboard has only 84 keys, so
not all of the scan-codes are used.

The only problems with the XT keyboard are the lock-status lights
(Caps-lock, Scroll-lock and Num-lock) and the key repeat mechanism.  The
lock-status lights can get out of sync with the computer's idea of which
lock keys are activated, but this only happens if someone resets the
keyboard by unplugging it temporarily.  When you hold a key down long
enough, the keyboard starts repeating the scan-code for that key.  The
release code is still only transmitted once, when the key is released.  The
problem here is that the delay to the start of the repeats and the repeat
rate were made too slow.  Of course, the keyboard really doesn't have to
handle repeat at all, since the computer knows when keys are pressed and
released and has a timer itself.  Old XT keyboard TSRs allowed you to adjust
the repeat delay and rate by duplicating the key repeat mechanism in the
computer.

Once IBM found that it had a nearly perfect keyboard it, of course, decided
that it had to be almost completely redesigned for the AT.  The keyboard
didn't have to be redesigned- there were enough extra scan-codes for the
AT's 101 key keyboard and the repeat mechanism could simply have been moved
to the BIOS.  But no, they had to redesign everything.  Sigh.

The AT uses a 5-pin DIN and the PS/2 uses a smaller connector with the same
signals:

     1     CLK/CTS (open-collector)
     2     RxD/TxD/RTS (open-collector)
     3     Not connected or Reset
     4     GND
     5     +5V

Now the interface is bi-directional.  When the computer wants to send a byte
to the keyboard, it asserts RTS and releases CTS.  If you're lucky, the
keyboard isn't deciding to transmit at the same time and it responds by
giving 10 clock pulses (at about 10000 baud) on the CLK line.  The computer
shifts a frame out on TxD on rising clock edges.  The frame format is now 1
start bit, 8 data bits and 1 odd parity bit.  The keyboard takes RTS being
held low as the first start bit, and the first data bit should be sent on
TxD after the first clock edge is received.  Yes, now you need a full UART
for the keyboard interface since you have to both transmit and receive and
generate and check parity (but it's still not RS-232- that would have been
too logical).  Why do you need parity checking on a three foot long keyboard
cable?  Because collisions can occur since the lines are so overloaded with
signals with different meanings and parity provides the means for detecting
these collisions.

The AT documentation says that pin 3 is "reserved", so the keyboard has to
provide its own reset.  But on the original AT, pin 3 was still Reset and
IBM's own keyboards at that time needed Reset (original AT keyboards won't
work on some old clones because of this).  Don't ask me... I don't
understand why they did this.

The protocol on the keyboard interface is now much more complicated.  These
bytes are defined:
 
Commands

  ED <byte>                 Set leds depending on byte
                              bit 0 is Scroll lock
                              bit 1 is Num lock
                              bit 2 is Caps lock

  EE                        Echo EE (for testing?)
  F0 <mode>                 Select mode 1, 2 or 3
  F2                        Send keyboard I.D.
  F3 <byte>                 Set repeat delay and rate
                              byte is: 0ddbbaaa
                              delay is (dd+1)*250 msec
                              rate is (8+aaa)*2^bb*4 msec

  F4                        Clear buffer
  F5                        Restore default settings and wait for enable
  F6                        Restore default settings
  FA                        Acknowledge
  FE                        Error- please retransmit
  FF                        Reset keyboard

Status returns

  00                        Buffer overflow
  AA                        Self-test passed
  F0 <scan-code>            Release code
  FA                        Acknowledge last command
  FD                        Self-test failed
  FC                        Self-test failed
  FE                        Last command in error; re-send
  E0 scan/release code      Extended keys in Mode 2

The computer and keyboard must acknowledge each command and key code with
either FA if there was no error, or FE if the last command/key-code should
be re-sent.  There are three modes of operation for the keyboard, depending
on which scan code assignments you want (these can often be set by a switch
on the back of keyboard, except that if mode 1 is selected from the switch,
the protocol is eliminated an the keyboard works exactly like an original XT
keyboard- newer keyboards only support modes 1 and 3).  In mode 1, the
keyboard gives XT scan-codes.  The keyboard handles the cursor keypad (which
didn't exist on the XT) by simulating pressing or releasing a shift key
(depending on whether shift or num-lock are pressed) and sending codes from
the numeric keypad.  Mode 2 works like mode 1, except that when the keyboard
does the weird stuff with the numeric keypad it prefixes everything with E0
and the release codes are the scan-codes prefixed with F0.  In mode 3, each
key gets a unique code and the release codes work as in mode 2: the release
are the scan-codes prefixed by F0.

When the AT keyboard is first reset it's supposed to send an AA if its
self-test passed or FD or FC if it failed.  But before it does this, it
sends a continual stream of AAs with the parity incorrect.  Once the
computer sends an FE to indicate that there is a parity error, the keyboard
stops sending bad AAs and sends a correct AA or an FD or FC.  This sounds
like someone made a quick fix in the keyboard firmware for mis-matched reset
timing (the keyboard always finishes resetting before the computer so the
computer could miss the AA/FD/FC).


Q) 3.27  Can I fake a keyboard so my computer will boot without it?

[From: jhallen@world.std.com (Joseph H Allen)]

() The IBM Keyboard - how do you use a computer without a keyboard?

Sometimes a PC needs to be set up as a "turn-key" system with no keyboard
for security reasons, or simply because the application doesn't need a
keyboard.  This causes a dead-lock problem when the system is booting: The
BIOS will detect that there is no keyboard and display the message "keyboard
failure - press F1 to continue," and the system becomes stuck.

There is usually a BIOS set-up option for disabling the keyboard test.
Check the manual for your motherboard.  If your BIOS does not have
this option, you're essentially screwed because there's no simple
solution.  You can't wire the DIN to fake the existence of a keyboard
since the BIOS checks for a self-test result code generated by the
keyboard.  You have to implement a small protocol (byte-by-byte
handshaking and ACK/NAK) to simulate a keyboard up to its self test.
There are adaptors available which contain a small microcontroller
programmed to do this.  Another solution is to replace your BIOS with
one which has the keyboard test disable option.  However, you have to
find one which matches your motherboard.



===============
Ralph Valentino (ralf@fs09.webo.dg.com) (ralf@wpi.edu)
Senior Hardware Engineer, AViiON System Development
Data General Corporation, Westboro, MA USA


From David.Steele@usask.ca Thu May 02 10:30:46 1996
Path: tribune.usask.ca!rover.ucs.ualberta.ca!unixg.ubc.ca!info.ucla.edu!newsfeed.internetmci.com!in1.uu.net!news.ultranet.com!bigboote.WPI.EDU!bigwpi.WPI.EDU!ralf
From: ralf@chpc.org (Ralph Valentino)
Newsgroups: comp.sys.ibm.pc.hardware.video,comp.sys.ibm.pc.hardware.comm,comp.sys.ibm.pc.hardware.storage,comp.sys.ibm.pc.hardware.cd-rom,comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.hardware.networking,comp.sys.ibm.pc.hardware.chips,comp.sys.ibm.pc.hardware.misc,comp.answers,news.answers
Subject: comp.sys.ibm.pc.hardware.* Frequently Asked Questions (FAQ) Part 3/5
Followup-To: comp.sys.ibm.pc.hardware.misc
Date: 19 Apr 1996 04:48:04 GMT
Organization: Worcester Polytechnic Institute
Lines: 1694
Approved: news-answers-request@MIT.EDU
Distribution: world
Expires: 31 May 1996 00:00:00 GMT
Message-ID: <4l75u4$em3@bigboote.WPI.EDU>
Reply-To: ralf@wpi.edu
NNTP-Posting-Host: bigwpi.wpi.edu
Summary: This is a monthly posting containing a list of Frequently
         Asked Questions (and their answers) pertaining to hardware
         and IBM PC clones.  It should be read by anyone who wishes
         to post to any group in the comp.sys.ibm.pc.hardware.*
         hierarchy.
Originator: ralf@bigwpi.WPI.EDU
Xref: tribune.usask.ca comp.sys.ibm.pc.hardware.video:68152 comp.sys.ibm.pc.hardware.comm:18560 comp.sys.ibm.pc.hardware.storage:68439 comp.sys.ibm.pc.hardware.cd-rom:32296 comp.sys.ibm.pc.hardware.systems:37518 comp.sys.ibm.pc.hardware.networking:12905 comp.sys.ibm.pc.hardware.chips:79453 comp.sys.ibm.pc.hardware.misc:60041 comp.answers:18200 news.answers:69847

Archive-name: pc-hardware-faq/part3
Last-modified: 1996/04/10
Version: 1.19

S) 4.0 Storage/Retrieval Devices

Q) 4.1  Why do I lose x Meg on my hard drive?
[From: Mike Long <mike.long@analog.com>]

The problem here is that there are two different measures of hard
drive storage, both called megabytes.  Computer hardware works on the
basis that one megabyte equals 2^20, or 1048576 bytes.  Hard drive
manufacturers, on the other hand, use a megabyte that has 1000000
bytes, because it makes the drive looks larger.  When buying a hard
drive, you should expect to lose almost 5% of what the manufacturer
claims the drive size to be.

The manufacturers are not totally at fault.  The first track of the
drive is used for the partition table and master boot record.  The
amount of data lost here depends on your drive parameters; usually
there are between 32 and 64 sectors (512 bytes/sector) on this first
track, so you lose between 16384 and 32768 bytes that way.

Additional space is taken up by two hidden files on your boot drive.
If you are running MS-DOS, these files are IO.SYS and MSDOS.SYS.  If
you are running PC-DOS, the names are IBMIO.COM and IBMDOS.COM.

[From: ralf@wpi.wpi.edu (Ralph Valentino)]

Many drives these days advertise unformatted capacity.  The actual
formatted capacity may be significantly lower than this as space is
taken up marking tracks, sectors, CRC's, etc.  Exactly how much lower
depends on the the size of the sectors.  For instance, placing 1k
sectors on the disk instead of the usual 512 byte ones may slightly
increase the usable storage space on the disk.  Note, however, that
many OS's insist you stick to the 512 byte sectors so this option is
best left alone.

A large number of drives also do auto-mapping of bad sectors; when a
sector goes bad, it will automatically use a spare it kept aside
during the format.  This is very handy as the OS never needs to deal
with the problem and some OS's, like DOS, will mark a whole cluster
bad when a single sector goes bad.  These spare sectors, as many as
one per track, remain hidden from the OS but still take up space on
your hard drive.

When you get to drives larger than 1.0 gig (SCSI), many host adapter
BIOS's can not deal with this as the BIOS was never designed to handle
more than 1024 cylinders, 64 heads, and 32 sectors per track. (1024 *
64 * 32 * 512bytes/sec = 1.0 gig).  Luckily, some OS's (like OS/2)
ignore the BIOS all together and read the actual geometry from the
disk itself.  If, however, you're not using such an OS and you notice
that you only have 1.0 gig available, you may want to check with the
manufacturer of your SCSI host adapter to see if a newer BIOS is
available.

Q) 4.2  *Should I get an IDE/floppy/SCSI/parallel port tape drive?
Q) 4.3  I have two floppies. Can I add a floppy based tape drive?
 
[From: herbst@techunix.technion.ac.il (Herbst OMR)]

It depends. On all modern tape drives: yes. Some old tape drives
cannot do this (my old Jumbo). If you have one of these, you will have
to buy either a 4-floppy controller or a dedicated tape controller.

Q) 4.4  How fast is a tape drive? Will a dedicated controller improve this?

[From: herbst@techunix.technion.ac.il (Herbst OMR)]

The tape connected through a floppy interface is limited to the floppy
speed.  On ATs 500Kbit/S. On old XT 250Kbit/S. With card support for
2.88MB floppy, 1Mbit/S. Many of the newer cards support this transfer
rate.
 
If the card operate at 500Kbit/S, a dedicated controller card will
speed up the tape by a factor of two.  In many cases, those cards do
hardware compression, helping even more.

Q) 4.5  What is QIC80, QIC40?
 
[From: herbst@techunix.technion.ac.il (Herbst OMR)]

QIC stands for Quarter-Inch Cartridge. QIC80 is the standard for 80MB
tapes, QIC40 for 40MB tapes. Both standard allows for extended length
cassettes of 300ft which gives 120MB and 60MB respectively.

Q) 4.6  How come I can't fit as much stuff on my tape drive as they claim?

Most tape drives these days advertise capacity with an expected
compression ratio of 2:1.  If you are backing up compressed files
(.Z,.ZIP, .ARC, .JPEG, and so forth) then the drive's own compression
scheme will not be as effective.  For these cases, the actual capacity
of the tape will be closer to the "uncompressed" capacity.

A table from herbst@techunix.technion.ac.il (Herbst OMR) shows:

  stated capacity     standard        tape length         # tracks
 
  80MB                QIC40           200ft (normal)      15
  120MB               QIC40           300ft (extended)    15
  160MB (rarely)      QIC80           200ft               28
  250MB               QIC80           300ft               28
 
  For all the recording density is 12500 ftpi; max tape speed is 90 ips.

A second reason is that some tapes assume you will be taking full
advantage of their "streamers".  Streaming collects a number of tape
blocks and writes them all at once, preventing the need for backing up
the tape after each block.  This positions the blocks closer together
on the tape.  If your backup program is slow, some streamers won't be
quite as effective.  If you hear the tape drive motor backing up the
tape alot on writes, this could be the case.

Q) 4.7  Are Colorado/Conner/Archive/... tapes compatible with each other?

[From: herbst@techunix.technion.ac.il (Herbst OMR)] 

If you use the same software: Yes. If you want to use different
software, then turn compression off. Compression done in software on
those drives is not compatible.

Q) 4.8  How does the drive/software know how long the tape is?

[From: herbst@techunix.technion.ac.il (Herbst OMR)]
 
The magnetic tape has holes in it. Inside the cassette enclosure there
is a small mirror. The drive sends an IR beam through it. Near the end
of tape the drive receives it. If the IR receiver is dusted, the drive
may 'reel off' the cassette.

Q) 4.9  What are all those QICs?

[From: herbst@techunix.technion.ac.il (Herbst OMR)]
 
(Thanks to Karl-Peter Huestegge and Jan Christiaan van Winkel)
QIC-11 is not an Industry Standard and there exist some incompatible
versions.
 
 Standard      Capacity      Tracks   Speed  Rec-density Flux-Trans Cartridges
 ----------------------------------------------------------------------------
 QIC-11     15/30MB (300ft)     4/9   90ips
            20/40MB (450ft)     4/9   90ips               6400ftpi  DC300XL
                                                         10000ftpi  DC300XLP
            27/60MB (600ft)     4/9   90ips              10000ftpi  DC600A
 
 QIC-24     45MB (450ft/137m)    9    90ips    8000bpi   10000ftpi
            55MB (555ft/169m)    9    90ips    8000bpi   10000ftpi
            60MB (600ft/183m)    9    90ips    8000bpi   10000ftpi  DC600A
 
 QIC-120   125MB (600ft/183m)    15   72ips   10000bpi   12500ftpi  DC600A
 
 QIC-150   155MB (600ft/183m)    18   72ips   10000bpi   12500ftpi  DC600XTD
                                                                    DC6150
 QIC-150   250MB (1000ft/305m)   18   72ips   10000bpi   12500ftpi
 
 QIC-320   320MB (600ft/183m)    26   72ips   16000bpi   20000ftpi  DC6320
 
 QIC-525   525MB (1000ft/305m)   26   72ips   16000bpi   20000ftpi  DC6525
 
* QIC-1000  1000MB (760ft)
 
* QIC-2GB
 
* QIC-10GB
 
Q) 4.10  Which QICs are read/write compatible?

[From: herbst@techunix.technion.ac.il (Herbst OMR)]

 The left column should be read: "Tape drives designed for the QIC-???
 standard *should* be able to read/write the following Tape formats:"
 
 TAPE-DRIVES     |                     Tape - Formats                      |
 designed for:   | QIC-11 | QIC-24 | QIC-120 | QIC-150 | QIC-320 | QIC-525 |
 ----------------|--------|--------|---------|---------|---------|---------|
 QIC-11          |  R  W  |        |         |         |         |         |
 QIC-24          |  R  W  | R   W  |  R      |         |         |         |
 QIC-120         |  R  -  | R   -  |  R   W  |  R      |         |         |
 QIC-150         |  R  -  | R   -  |  R   W  |  R   W  |         |         |
 QIC-320         |  R  -  | R   -  |  R   W  |  R   W  |  R   W  |  ?   ?  |
 QIC-525         |  R     | R      |  R   W  |  R   W  |  R   W  |  R   W  |
 ---------------------------------------------------------------------------

Q) 4.11  What is the CMOS/jumper setting for my hard drive?
[From: Carsten Grammes (cagr@rz.uni-sb.de)]

                    Configuration of IDE Harddisks
                    ==============================


last update: 24 March 1994

collected by Carsten Grammes (cagr@rz.uni-sb.de)
and published on comp.sys.ibm.pc.hardware as part of the FAQ.



!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
There is explicitly NO WARRANTY that the given settings are correct or
harmless. (I only collect, I do not check for myself!!!). There is
always the possibility that the settings may destroy your hardware!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


Since I hope however that only well-minded people undergo the effort of
posting their settings the chance of applicability exists. If you should
agree or disagree with some setting, let me know immediately in order
to update the list.

If you possess a HD not mentioned here of which you know BIOS and/or
jumper settings, please mail them to me for the next update of the list!

Only IDE (AT-Bus) Harddisks will be accounted for.  If not specified the
Landing Zone should be set equal to the number of cylinders. If not
specified the 'Write Precompensation' should be set 65535. (There are
BIOSes that don't even ask for it).  On most IDE disks these values are
dummies, relicts from old MFM times.

The capacity given here is sometimes in Megabytes (1000000 bytes) and
sometimes in MB (1048576 bytes). Don't worry! The only right way to calculate
the capacity is
    cyl * heads * sec/tr * 512 
which gives the capacity in bytes!  Dividing by 1000000 or 1048576 gives
the capacity in Megabytes or MB respectively.

If you get problems when installing 2 HD's with correct BIOS and jumper
settings, try to swap drive 1 and 2, often that helps.

Please don't flame me because of the 'layout' of the list. Since the
available information is so strongly varying I often only pack _YOUR_
mail to me into the list. If someone feels encouraged to improve this,
I would be glad to receive a 'lifted' version. But there should be all
info contained!

Since the list is rather long, I give here a summary of all drives
described therein.

************* ALPS Alps alps
DR311C

************* CDC Cdc cdc
BJ7D5A   94155-48   94335-100  94166-141   94171-300  736 SABRE
BJ7D5A   94295-51   94355-55   94166-182   94171-344  850 SABRE
BJ7D5A   94155-57   94355-100  94186-383   94181-574  1230 SABRE
94155-21 94155-67   94155-135  94186-383H  94208-51
94155-25 94155-77   94205-77   94186-442   94211-91
94155-28 94155-85   94355-150  94216-106   94221-190
94155-36 94155-86   94335-150  94356-200   94351-172
94155-38 94205-51   94156-48   94161-86    368 SABRE
94335-55 94156-67   94166-101  94161-121   500 SABRE

************* CONNER Conner conner
CP342   CP2034   CP2084   CP3044  CP3104  CP3204  CP30084
CP344   CP2044   CP3000   CP2124  CP3111  CP3204F CP30104
CP2024  CP2064   CP3024   CP3184  CP3114  CP30064 CP30084E

CP30174E  CP30174E  CP3304  CP3544
CP30204   CP30204   CP3364  CP3554
CP30254   CP30254   CP3504  CP30101

************* FUJITSU Fujitsu fujitsu
M2611T  M2612ET  M2613ET  M2614ET  M2618T  M2622T  M2623T  M2624T

************* HEWLETT PACKARD Hewlett Packard hewlett packard HP Hp hp
C2233

************* IBM Ibm ibm
WDA-L160   WDA-L42   IBM 85 MB IDE (number not known)

************* JVC Jvc jvc
JD-E2085M

************* KALOK Kalok kalok
KL3100 KL3120

************* MAXTOR Maxtor maxtor
LXT-200A  2585A  7120A
LXT-213A  7040A  7131AT
LXT-340A  7060A  7213A
LXT437A   7080A  7245A
LXT535A

************* MICROPOLIS Micropolis micropolis
2105A     2112A

************* MICROSCIENCE Microscience microscience
7100-00  8040-00  7070-20  7100-00  7100-20  8040

************* MINISCRIBE Miniscribe miniscribe
8225AT  8051AT  8450AT

************* NEC Nec nec
D3735  D3755  D3756  D3741

************* QUANTUM Quantum quantum
40AT     LPS52AT      ELS42AT
80AT     LPS80AT      ELS85AT
120AT    LPS105AT     ELS127AT
170AT    LPS120AT     ELS170AT
210AT    LPS170AT     LPS540A
425AT    LPS240AT

************* RODIME Rodime rodime
RO3058A  RO3088A  RO3095A  RO3128A  RO3135A  RO3059A  RO3089A
RO3129A  RO3139A  RO3209A  RO3259A

************* SAMSUNG Samsung samsung
SHD-3101A  SHD-3061A  SHD-3062A

************* SEAGATE Seagate seagate
ST1057a     ST1144a     ST138a      ST274a      ST3283a
ST1090a     ST1156a     ST1400a     ST280a      ST351ax
ST1102a     ST1162a     ST1401a     ST3051a     ST9051a
ST1111a     ST1186a     ST1480a     ST3096a     ST9077a
ST1126a     ST1201a     ST157a      ST3120a     ST9096a
ST1133a     ST1239a     ST2274a     ST3144a     ST9144a
ST3243A     ST125a      ST2383a     ST325ax
ST351AX
ST9235A     (maybe others)

************* TEAC Teac teac
SD-3105

************* TOSHIBA Toshiba toshiba
MK1122FC  MK2024FC  MK2124FC  MK2224FC  MK234FCH  MK234FCF

************* WESTERN DIGITAL Western Digital western digital
WDAC140  WDAC280  WDAC1170  WDAC2120  WDAC2170  WDAC2200  WDAC2250
WDAC2340 WDAC2420 WD93044-A WDAH260   WDAH280   WDAP4200
WD93048A



And here it comes...


************* ALPS Alps alps *************

Manufacturer: ALPS ELECTRIC Co.

BIOS settings:
Model   Heads  Cylinders  Sectors  L-Zone Size
DR311C   14      868        17      868   105 MB

(Real geometry of drive:
   2108 cyl.  2 heads  49 sectors/track
   32k internal cache)

Jumpers:
  C/D
 -ACT
 -DSP
 -HSP
  MS3
  SYNC
  DC
  MS0
  MS1
  MS2

Master drive & no slaves present: jumpers on C/D and -ACT.
No other jumpers installed, function unknown.


***************************   C D C ***********************************

I have the feeling that not all of these are IDE...

-------------------------------------------------------------------------------
MODEL    ST-506         CAP   CYL  H  RWC  WPC ENC  RATE ACCESS  SPT COMMENTS
-------------------------------------------------------------------------------
BJ7D5A  77731614 5.25FH  23   670  4  375  375 M    5             17
BJ7D5A  77731608 5.25FH  29   670  5  375  375 M    5             17
BJ7D5A  77731613              733  5  -    -        5             17
94155-21 WREN-1 5.25FH   21   697  3  698  698 M    5    28 MS    17
94155-25                 24   697  4  698  128 M    5             17
94155-28                 24   697  4  698  128 M    5             17
94155-36 WREN-1 5.25FH   36   697  5  698  698 M    5    28 MS    17
94155-38                 31   733  5  734  128 M    5             17
94155-48 WREN-2 5.25FH   40   925  5  926  926 M    5    28 MS    17
94295-51 WREN-2 5.25FH   43   989  5  990  990 M    5    28 MS    17
94155-57 WREN-2 5.25FH   48   925  6  926  926 M    5    28 MS    17
94155-67 WREN-2 5.25FH   56   925  7  926  926 M    5    28 MS    17
94155-77 WREN-2          64   925  8  926  926 M    5             17
94155-85 WREN-2 5.25FH   71  1024  8   -    -  M    5    28 MS    17
94155-86 WREN-2 5.25FH   72   925  9  926  926 M    5    28 MS    17
94205-51       5.25HH    43   989  5  990  128 M    5    32 MS    17
94335-55        3.5"     46  -     5   -    -  M    5    25 MS    17
94335-100       3.5"     83  -     9   -    -  M    5    25 MS    17
94355-55   SWIFT-2 3.5"  46  -     5   -    -  M    5    16.5 MS  17
94355-100       3.5"     83  -     9   -    -  M    5    16.5 MS  17
    ST-506 RLL
94155-135 WREN-2 5.25HH  115  960  9   -    -  R    7.5  28 MS    26
94205-77  WREN-2 5.25HH  63   989  5   -    -  R    7.5  28 MS    26
94355-150        3.5"    128 -     9   -    -  R    7.5  16.5 MS  26
94335-150        3.5"    128 -     9   -    -  R    7.5  25 MS    26
    ESDI
94156-48   WREN-2        40   925  5  926  926 N    5    28 MS
94156-67   WREN-2        56   925  7  926  926 N    5
94156-86   WREN-2        72   925  9  926  926 N    5
94166-101  WREN-3 5.25FH 86   969  5  970  970 N    10   16.5 MS
94166-141  WREN-3 5.25FH 121  969  7  970  970 N    10   16.5 MS
94166-182  WREN-3 5.25FH 155  969  9  970  970 N    10   16.5 MS
94186-383  WREN V 5.25FH 383 1412 13   -    -  R/N  10   8.3 MS
94186-383H WREN V 5.25FH 383 1224 15   -    -  R/N  10   14.5 MS
94186-442  WREN V 5.25FH 442 1412 15   -    -  R/N  10   16 MS
94216-106  WREN-3 5.25FH 91   969  -   -    -  N    10   16.5 MS
94356-200  SWIFT 3 3.5"  172 -     9   -    -  R/N  10   16.5 MS
WREN III          5.25HH 106  969  5   -    -  R/N  10   18 MS
    SCSI
94161-86   WREN-3 5.25FH 86   969  -   -    -            16.5 MS
94161-121  WREN-3 5.25FH 121  969  -   -    -            16.5 MS
94171-300  WREN-4 5.25FH 300 1365  9   -    -  R         16.5 MS
94171-344  WREN V 5.25FH 344 1549  9   -    -  Z    9-15 17.5 MS
94181-574  WREN V 5.25FH 574 1549 15   -    -  Z    9-15 16 MS
94208-51
94211-91   WREN-3 5.25FH 91   969  -   -    -            16.5 MS
94221-190  WREN V 5.25HH 190 1547  5   -    -  R    10-15 8.3 MS
94351-172  SWIFT 4 3.5"  172 -     9   -    -       10   16.5MS
WREN III         5.25HH  106  969  5   -    -  R/N  10   18 MS
    SMD
368 SABRE  8"            368 -    10   -    -       1.8  18 MS
500 SABRE  8"            500 -    10   -    -       2.4  18 MS
736 SABRE  8"            741 -    15   -    -       1.8  16 MS
850 SABRE  8"            851 -    15   -    -       2.4  16 MS
1230 SABRE 8"           1236 1635 15   -    -       2.4
-------------------------------------------------------------------------------

    CAP   = CAPACITY IN FORMATTED MEGABYTES
    CYL   = MAXIMUM NUMBER OF CYLINDER
    H     = NUMBER OF DATA HEADS
    RWC   = START REDUCED WRITE CURRENT
    WPC   = START WRITE PRECOMP
    ENC   = ENCODING METHOD R=RLL, M=MFM,Z=ZBR
    RATE  = TRANSFER RATE IN MEGABITS/SEC
    ACCESS= AVERAGE ACCESS TIME
    SPT   = SECTORS/TRACK X 512 bytes
    FH    = FULL HIGH FORM FACTOR
    HH    = HALF HIGH FORM FACTOR
    R     = RLL (run length limited)
    N     = NRZ (non return to zero)
    M     = MFM (modified frequency modulation)
    SA    = STAND ALONE
    Z     = ZBR

Jumpers are not know (yet).


************************** CONNER Conner conner **************************

Conner drives are low level formatted at the factory. It is only necessary to r
un SETUP, FDISK and DOS FORMAT.
          
Model     Hds  Cyls  Sec    Pcomp  L-Zone    Type    Table  LED
CP342     4    805   26       0    805        17       n/a  A
CP344     4    805   26       0    805        17       1    A
CP2024    2    653   32       0    653         2       3    n/a
CP2034    2    823   38       0    823       *UT       3    n/a
CP2044    4    552   38       0    552        17       3    n/a
CP2064    4    823   38       0    823       *UT       3    n/a
CP2084    8    548   38       0    548       *UT       3    n/a  
CP3000    2   1047   40       0   1047        17       1    A
CP3024    2    636   33       0    636         2       1    A
CP3044    1   1047   40       0   1047        17       1    A
          5    980   17   (also reported)
CP2124    8    560   53       0    560       *UT       3    n/a
CP3184    6    832   33       0    832       *UT       1    A
CP3104    8    776   33       0    776       *UT       1    A
CP3111    8    833   33       0    833       *UT       1    A(?)
CP3114    8    832   33       0    832       *UT       1    A
CP3204    16   683   38       0    683       *UT       2    B
CP3204F   16   683   38       0    683       *UT       3    B
CP30064   4    762   39       0    762       *UT       2    B
CP30084   8    526   39       0    526       *UT       2    B
CP30104   8    762   39       0    762       *UT       2    B
CP30084E  4    903   46       0    903       *UT       4    C
CP30174E  8    903   46       0    903       *UT       4    C
CP30204   16   683   38       0    683       *UT       4    C
CP30254   see below
CP3304    16   659   63       0    659       *UT       4    D 
CP3364    16   702   63       0    702       *UT       4    C
CP3504    16   987   63       0    987       *UT       4    D
CP3544    16   1024  63       0    1024      *UT       4    C
CP3554    16   1054  63       0    1054      *UT       3    B

Table 1 jumper settings: 
     Single drive = Jumper ACT and C/D 
     Master drive = Jumper ACT, C/D and DSP.
     Slave drive = No jumpers installed.

Table 2 jumper settings:
     Single drive = Jumper E2
     Master drive = Jumper E1 & E2
     Slave drive = No jumpers installed.

Table 3 jumper settings:
     Single Drive = Jumper C/D
     Master Drive = Jumper C/D and DSP
     Slave Drive = No jumpers installed

Table 4 jumper settings:
     Single and Master drive = Jumper C/D
     Slave drive = no jumper




ALL CONNER 20 MBYTE DRIVES USE DRIVE TYPE 2. ALL CONNER 40 MBYTE DRIVES USE DRI
VE TYPE 17.                                        * 

UT = Universal translate. Select a drive type that is close to, but does not ex
ceed the megabyte capacity of the drive. The drive will translate to the megaby
te capacity you have selected.

 LED
A: J-4         B: J-1         C: J-5         D: J-3
Pin 1 = +      Pin 3 = +      Pin 3 = +      Pin 3 = +
Pin 2 = -      Pin 4 = -      Pin 4 = -      Pin 4 = -

Conner drives are low level formatted at the factory. It is only necessary
to run SETUP, FDISK, and DOS FORMAT.

Comment concerning CP3000 jumpers:

   According to your list, all Conners should be 2 or 3 jumpers only.
That's why I'm puzzled with the 4-jumper Conner CP-3000.
In addition to the common jumpers present in
Conner - C/D, DSP & ACT, there is an extra one: HSP
By trial and error, HSP seems to follow DSP setting.


> When I installed a Conner CP3204F (203 MB) as master and a WD Caviar 2200
> (203 MB) as slave, both with and without the "CP" jumper, the Caviar had
> seemingly normal behaviour. However, when doing writes to the Caviar, once
> in a while it would overwrite directories etc. Using FASTBACK was almost
> impossible.
> 
> The workaround is to install the Caviar as the master, and the Conner
> as the slave.

and:
information: I am slaving a Conner CP3000 40Meg to a Western Digital
Caviar 2200 212 Meg.

the results: I first found out that pin 1 on the CP3000 was LABELED
INCORRECTLY on the PC board....had to flip the IDE cable (which made the
cable install much more cleanly- no flips....shoulda been my first clue
that something was not correct, oh well)

next: I had to DOS-format the CP3000 ALONE on the PC system before it
wanted to work with the WD caviar.... weird
also: the WD Caviar is partitioned: C:\ was the first 100 Meg and D:\ was
the second 100 Meg.  After the CMOS was correctly configured and the
drives brought online, the PC AUTOMATICALLY assigned the drives as thus:
C:\ first 100 Meg partition on the WD
D:\ 40 Meg Conner
E:\ second 100 Meg partition on the WD
even FDISK reports the above.  


Conner CP 30254

Capacity: 250 MB
Dimensions: 3,5 inch, lowprofile (1 inch)
IDE interface
                         Cylinders Heads Sectors

Physical specs.:         1985      4     62
Logical specs.:          895       10    55

seek time 12 ms
Rotation speed 4542 rpm

jumpers         C/D
1 drive master  Y
2 drive master  Y
2 drive slave   N/Y


----

Subject: Re: Conner CP 30254

I tried several combination and even called Conner for info on
configuring two Conner drives as master (301??, a 300+ M Connder
drive) and slave (30254).  The jumpers that worked are:

                Pins    Jumpers
Master          1-2        Y     (factory setting)
                3-4        Y     (factory setting)

Slave           1-2        N
                3-4        Y     (factory setting)

So the C/D should mape to Y/N instead of N/Y in the table.
--
Some notes made whilst configuring a pair of Conner IDE drives
for Master/Slave operation from Hyundai Super-LT6 Laptop 386sx-20.

Final Working Configuration

Drive 1:        CP3000  40 Mb   Type 17
977 cyl 5 hds   17 sec/trk      Pre 300 LZ 977

Verified configuration as per Grammes' list. HSP does need to
follow DSP (empirically) - failure to do so produced behaviour
such as LCD screen display scrambling on ROM boot.

Single, Master and Slave configurations all checked out.

Drive 2:  CFA170A 170 Mb  Unknown type
332 cyl 16 hds  63 sec/trk      Pre --- LZ ---

Did not appear on Grammes' list. Successful configuration resulted
close to that shown as Table 3 for Conner drives, as follows:

        Single          2 links         (not C)/D and (not A)/(?)
        Master          1 link          (not C)/D
        Slave           0 links

One link is listed here as (not A)/(?) due to a hole being drilled
through the (?) part of the silk screening ...

The drives worked together as either slave or master ...
--
Connor CP30101
760 cyl, 8 hds, Precomp -1, Landing 760, Sec/Track 39, ECC 7 Capacity 121.41M


Model CP342 disk (40 Meg IDE drive)
  Single Drive: E5, E7 jumpers IN
  Master Drive: E6, E7 jumpers IN
  Slave Drive:  E7 jumper IN

In addition, this is an old disk drive.  It was factory configured to
use 3:1 interleave.  This can cause timing problems with newer disk
drives that are configured for 1:1 interleave when using the same IDE
controller.  The CONNER tech support person suggested I only use the
CONNER drive as a SLAVE with the newer disk as the MASTER.

This configuration (MAXTOR 7345A as MASTER and CONNER CP342 as SLAVE)
has now been in use for over a week and seems to be working fine.


************************  FUJITSU Fujitsu fujitsu  ***************************

DETAILS OF FUJITSU DRIVES M261xT (Standard)

                   M2614ET     M2613ET     M2612ET     M2611T

Heads (physical)       8           6           4           2
Cyl (physical)      1334        1334        1334        1334
Sec/trk               33          33          33          33
Speed (rpm)         3490        3490        3490        3490
Capacity           180MB       135MB        90MB        45MB


              +-----------------------------------------------+
              |                                               |
              +--+                                            |
        PSU   |  |      CNH-2                                 |
              +--+          1                                 |
            1 |  |          .                    LED          |
              |  | CNH-1    9      CNH-3      Connector       |
              |  |   1           6..1            o o          |
      40-way  |  |   .                           | |          |
        IDE   |  |   .                                        |
              |  |   .                                        |
              |  |  12                                        |
              +--+                                            |
              +-----------------------------------------------+



                 Pin        Function
                 Position

                 *  1- 2    Active mode
                    2- 3    Slave present mode
                    4- 5    Pin 27=IOCHRDY
CNH-1 JUMPERS    *  5- 6    Pin 27=RESERVED
                    7- 8    2 drive system
                 *  8- 9    1 drive system
                   10-11    Pin 29=IRQ14 : Pin 31=RESERVED
                 * 11-12    Pin 31=IRQ14 : Pin 29=RESERVED


                 Pin        Function
                 Position

                    1- 2    SLAVE drive mode
CNH-2 JUMPERS    *  4- 5    MASTER drive mode
                    7- 8    ECC 4 bytes
                 *  8- 9    ECC 7 bytes


                 Pin        Function
                 Position

                    1- 2    Write protect enabled
CNH-3 JUMPERS    *  2- 3    Write protect disabled
                    4- 5 -6 Reserved

Key:  * (I guess!) marks factory default setting for jumper


BIOS SETTINGS

BIOS setting for the M2614ET in my system is 667 cylinders, 33 sectors
and 16 heads.

> I was trying to set my IDE drive in the subject above to a slave drive for
> A Conner 170MB drive and contacting the support company gave me this answer (w
hich works). The factory default on SW2 is On Off Off Off Off Off (1-6). This se
ts the drive to be a single drive. Setting SW2 to Off On On Off Off Off makes it
 a slave drive. SW1 has been set to On Off Off On (1-4) all along.



MODEL      CYLINDERS   HEADS    SECTORS   CAPACITY (Million bytes)

M2622T      1013        10        63         326.75
M2623T      1002        13        63         420.16
M2624T      995         16        63         513.51


There are 6 switches on the switch block on these drives.  Only 4 of 
them have a use that I am aware of (from my M2624T manual):

Master/Slave        Master (*)      SW1-5 OFF
                    Slave           SW1-5 ON
ECC bytes           4 bytes (*)     SW1-4 OFF
                    7 bytes         SW1-4 ON
Write Protect       Disabled (*)    SW1-3 OFF
                    Enabled         SW1-3 ON
IO Channel Ready    Disabled (*)    SW1-1 OFF
                    Enabled         SW1-1 ON

I have no idea about the function of SW1-2 and SW1-6.  The values 
listed with a (*) are the factory default settings.


M2618T  202MB   Cyl/hd/spt  718 12 48


*********************   Hewlett Packard   ****************************
HEWLETT PACKARD Hewlett Packard hewlett packard HP Hp hp

C2233   227 MB  Cyl/hd/spt  733 12 53


*********************   IBM Ibm ibm   ****************************

WDA-L160    163 MB      Cyl/hd/spt  984 10 34
WDA-L42     42MB        Cyl/hd/spt  977 5 17

Jumpers for IBM WDA-L160:

Fit JP2 for Master or single drive

Remove JP2 and fit JP3 for Slave

JP1 appears to be always fitted.

Functions of other jumpers unknown at present.

Position of jumpers:

                -----------------------------------------
                |          Drive Mechanism              |
                |                                       |
                -----------------------------------------
                                PCB             . . . . 
                                                . . . .

                                        JP      4 3 2 1 


Also:

IBM 85 M IDE (number not known)

10 Heads        984 Cylinders           17 Sectors      0 WPC   984 LZ

Patches as for L160 above


*********************   JVC Jvc jvc   ****************************

JD-E2085M   79 MB       Cyl/hd/spt  973 4 43


***********************    KALOK Kalok kalok    ***************************

KALOK   KL3100    105 MB
BIOS:   cyl 979     heads 6     sectors 35

KALOK   KL3120    120 MB
BIOS:    Cyl 981     heads 6     sectors 40

The following jumper settings have been reported for KL3100 but are probably
also valid for other Kalok drives.

Single HD:
o o o o o

o o o o-o    <-- same row as pin 1 of the IDE connector.

Master (disk 1):
o o o o o
    |
o o o o o

Slave:
o o o o o
      |
o o o o o

These 5 pairs of pins are at the righthand side of the disk.



************************   MAXTOR Maxtor maxtor   ***************************

Model           Cyls    Heads   Sectors Precomp Landing Zone
----------      -----   -----   ------- ------- ------------
LXT-200A        816     15      32      0       816
LXT-213A        683     16      38      0       683
LXT-340A        654     16      63      0       654
LXT437A         842     16      63      0       842
LXT535A         1036    16      63      0       1024

Jumpers are as follows:

The bottom of the drive looks like this (well, sort of):

|        o o 1-2             |
|        o o 3-4             |
|        o o 5-6             |
|        o o 7-8             |
|        o o 9-10            |
|                            |
+[POWER] [IDE CONNECTOR]-----+

                                Single drive      Dual Drive System
Pin numbers     Jumper          System          Master          Slave
-----------     ------          ------------    ------          -----
1-2             Slave Drive     remove          remove          install
3-4             Activity LED    optional        optional        optional
5-6             Slave Present   remove          remove          optional
7-8             Master Drive    remove          install         remove
9-10            Sync Spindle    remove (n/a)    optional*       remove

* only one drive (the master) in an array should have this jumper installed.


                Hd    Cyl   spt
Maxtor 2585A    10    981   17

Maxtor 7060A    16    467   17     62,0 J14 closed, J13 closed
Maxtor 7060A     7   1024   17     59,5 J14 open,   J13 open
Maxtor 7060A     4    762   39     58,0 J14 closed, J13 open
Maxtor 7060A     8    925   17     57,9 J14 open,   J13 closed

Maxtor 7120A    16    936   17    124,3 J14 closed, J13 closed
Maxtor 7120A    14   1024   17    119,0 j14 open,   J13 open
Maxtor 7120A     8    762   39    116,0 J14 closed, J13 open
Maxtor 7120A    15    900   17    112,0 J14 open,   J13 closed
Maxtor 7120A     8    824   33    106,2 J14

Jumpers for the above 2 drives:

                  J11  I/O-channel ready ( open: disabled; close: enabled )
                  J13  see above
                  J14  see above
                  J15  operation-status ( open: normal; close: factory )
       J J J J J            
       2 1 1 1 1
       0 9 8 7 6

Power  data-cable

J16: Idle mode latch ( open: disabled; close: enabled )
J17: drive model ( open: 7060A; close 7120A )
J18: ECC Bytes ( open: 7 bytes; close: 4 bytes )

Master/Slave: drive is master and alone    : J20 closed, J19 closed
              drive is master of two drives: J20 closed, J19 open
              drive is slave of two drives : J20 open  , J19 closed


Maxtor 7213A

Default (power-up) AT BIOS Translation Parameters (others possible)
Cyl   Hds  SpT  MBytes
683   16   38   212

There are two sets of jumpers. A set of 5 and a set of
4. With the power and IDE connector toward you, the set of 5 is
numbered (left to right) J16 - J20  , and the set of 4 is numbered
(bottom to top) J22-J25. 

The only jumper of normal interest is J20. Jumper it for only
drive in a single drive system, or master drive in a dual drive
system.
 
Remove the jumper J20 for slave drive in a dual drive system. 

J19 is a dummy and may be used to store the spare shunt if the 
drive is configured for a slave mode.

Jumpers J17, J18, J24, J25 are factory reserved. Abnormal operation
may occur if jumpered.

Jumper 22 is sync spindle enabled/disabled  (open=disabled)
Jumper 23 is sync slave/master              (open=slave)
Jumper 16 is I/O Channel Ready              (open=disabled)


Maxtor 7245A (245Mb IDE; self-parking; Universal Translate):
Drive type : User defineable
Cyl    Hds    WPC    LZ     S/T
967    16     0      0      31      (WPC and LZ optional)

Master(2):  J20 closed
Slave(2):   J20 open (use J19 for shunt storage)
Single:     J20 closed


 
 Basic Specifications                                       
 -------------------------------------------------------------------
         Formated              Data          Sect.         Average
 Model   Capacity   Cylinders  Heads  Disks  Track  Cache  Seek Time
 7080A   82.2 MB    1.170      4      2      36     32k    17ms  
 7040A   41.1 MB    1.170      2      1      36     32k    17ms  
 
 AT BIOS Translation Parameters
 ---------------------------------+---------------------------------
 Model  Cyls  Heads  Spt   MB     |  Model   Cyls  Heads  Spt   MB
 7080A  1039    9    18    82.1   |  7040A   524     4    40    40.9 
         981   10    17    81.4   |          981     4    17    40.7 
         832    6    33    80.4   |          977     5    17    40.5  
         497   10    33    80.0   |                                 
        1024    9    17    76.5   |                                 
 
 Technical Notes:
 ------------------------------------------------------------------------
 * The WPC and Landing Zone BIOS entieres do not need a specific number 
   for proper operation. Maxtor AT interface hard drives will ignore and
   override any numbers programmed.             

 * Drive is low-level formated with 1:1 interleave at factory, with any 
   defects retired to a dedicated non-destructive zone.
 
 * The drive's on-board controller will auto-translate every cylinder, 
   head, and SPT combination listed in the parameters table. Therefore, 
   configuration jumpers J13 and J14 are not required for most AT BIOS 
   setup applications.

 * The 7080A is shipped with J17-J20 jumered and the 7040A is shipped 
   with J18-J20 jumpered to operate as single AT IDE drives. J20 and J19 
   control master/slave operation.
 
 7080A / 7040A Jumper Designation
 ------------------------------------------------------------------------
 Jumper   |               21111    1111  |  J3 1 +12V DC      J7 1 +5V
 Position |               09876    5431  |     2 +12V Ground     2 +12V
          |                              |     3 +5V Ground      3 Ground
 Pins     +[4321]--[1            ]--[321]+     4 +5V DC
         J3 Power     Data Cable   J7 Power

 J20 J19  Master/Slave Select    (*) Single Drive   closed, closed
                                     Master (Dual)  closed, open
                                     Slave (Dual)   open, closed
 J18      ECC Bytes              (*) closed 4 Bytes / open 7 Bytes
 J17      Drive Model                open 7040A / closed 7080A
 J16      Idle Mode Latch        (*) open disabled / closed enabled
 J15      Reserved for Factory   (*) open normal / closed factory
 J11      I/O Channel Ready      (*) open disabled  /  closed enabled
 J14 J13  Default Configuration at Power Up
          Cyls  Heads  SpT  MB     J14     J13     (J17)
 40MB (*)  981    5    17   40.7   open    open    open 
           524    4    40   40.9   open    closed  open
 80MB (*)  981   10    17   81.4   open    open    closed
           832    6    33   80.4   open    closed  closed
          1024    9    17   76.5   closed  open    closed
 (60MB)    762    4    39   58.0   closed  closed  closed       
 ------------------------------------------------------------------------
 (*) = Default      Note:  A spare jumper is supplied across J13 and J14.



>I have a 7131AT maxtor in my machine and setup info as follows:
>
>                1002 cylinders
>                8 heads
>                32 sectors
>                0 precomp
>                1002 LZ
>

********************* MICROPOLIS Micropolis micropolis ***********************


Drive           2105A           2112A
----------------------------------------
Unformatted MB  647             1220
Formatted MB    560             1050
Platters        5               8
Heads           8               15
Cylinders       1760            1760
----------------------------------------

Performance (both):

        Track to track (read)           1.5 msec
        Track to track (write)          2.5 msec
        Average                         10 msec
        Max                             25 msec
        Avg Rotational Latency          5.56 msec
        Rotational speed                5400 rpm (+/- 5%)
        Data Transfer Rate              upto 5Mbytes/sec
        Internal data rate              24-40 Mbits/sec

BIOS Settings:

2105A           1084 cyl        16 heads        63 sectors
2112A*  master  1024 cyl        16 heads        63 sectors
        slave   1010 cyl        16 heads        63 sectors
                
* the 2112A emulates both master and slave


Jumpers (labelled J6 on the drive)

        ----
        |oo| W1\ only these 2 are used
        |oo| W2/
        |oo|
        |oo|
        |oo|
        ----

        W2      W1
        --      --
        in      in      2112A only - drive emulates both master + slave
        in      out     Drive is master, slave is present
        out     in      Drive is slave
        out     out     Drive is master, no slave present (ie single drive)


*****************   MICROSCIENCE Microscience microscience   *****************

MicroScience 

Model: 7100-00
Heads: 7
Cylinders: 855
S/T: 35 (?)
Size: 105M


Model # 8040-00.
Size 40M  5hd/17sec/977cyl

Model   # cyls  # heads spt     lz      precomp         cap (formatted)
7070-20 960     5       35      960     960             86 MB
7100-00 855     7       35      855     855             107 MB
7100-20 960     7       35      960     960             120 MB
8040    1024    2       40      1024    1024            41 MB

(NOTE: I have no jumper information on the model 8040)
On the 7xxx series the jumper pins are bent parallel to the board. When 
they are pointing toward you #1 is on the left, there are 8 altogether.

single drive            all open
master drive            1-2 shorted
slave drive             7-8 shorted


***************   MINISCRIBE Miniscribe miniscribe    ************************

Miniscribe

MODEL   AT               CAP   CYC  H  RWC  WPC ENC  RATE ACCESS  SPT COMMENTS 
8225AT            3.5"    21   745  2  -    -        8    28 MS    28
8051AT            3.5"    42   745  4  -    -        8    28 MS    28
8450AT            3.5"    42   745  4  -    -        8    40 MS    28

Master(2):  5-6
Slave(2):   1-2
Single:     1-3 (shunt storage)


***************************   NEC Nec nec   *********************************

NEC     D3735,  40 MB
BIOS:   Cyl 537     Head 4      sect 41

NEC     D3755,  105 MB
BIOS:   Cyl 625     Head 8      sect 41

NEC     D3756, 105 MB
BIOS:   Cyl 1005    Head 12     sect 17

NEC     D3741,  44 MB
BIOS:   Cyl 423     Head 8      sect 26         WPcom 0         LZone 424
 

Jumper  JP12    JP13        (for all above NEC drives)
Single  0       0
Master  1       0
Slave   1       1

There have been reported difficulties in using WD Caviar as Master and
NEC drives as slave - the other way it works.



************************  QUANTUM Quantum quantum   *************************

Logical Specs for Quantum AT Drives
COMPLIMENTS OF COMPUTER BROKERS OF CANADA


Model       Cap     Avg Acc     Cylinders     Heads    Sectors/Track
            (MB)     (ms)

40AT        42        19           965          5            17
80AT        84        19           965         10            17
120AT       120       15           814          9            32
170AT       168       15           968         10            34
210AT       209       15           873         13            36
425AT       426       14          1021         16            51
LPS  52AT   52        17           751          8            17
LPS  80AT   83        17           611         16            17
LPS 105AT   105       17           755         16            17
LPS 120AT   122       16           901          5            53
LPS 170AT   160       15           968         10            34
LPS 240AT   245       16           723         13            51
LPS 540A    see below

=================================================
Legend:  1=Jumper Installed  0=No Jumper
=================================================

40 & 80 AT Jumpers

DS  SS   Meaning
1   0    Single drive configuration
1   1    Master of dual drive
0   0    Slave of dual drive
0   1    Self-Seek Test

=======================================================

120, 170, 210 & 425 AT Jumpers

DS  SP  SS   Meaning
0   0   0    Slave when the Master is Quantum PRODRIVE other than 40/80A
0   0   1    Slave in PRODRIVE 40/80A mode
0   1   0    Slave when Master is non Quantum Drive
0   1   1    Not Used
1   0   1    Master drive PDIAG mode checking DASP for slave
1   1   0    Master in PDIAG mode using SP to check if slave present
1   1   1    Master in 40/80A mode using SP to check if slave present
1   0   0    Single drive

=======================================================

LPS 52, 80, 105, 120, 170 & 240 AT Jumpers
DS  SP  DM*  Meaning
0   0   0    Slave in standard PDIAG mode for compatibility with drives that use
             PDIAG-line to handle Master/Slave communications
0   0   1    Slave in PRODRIVE 40/80A mode compat. without using PDIAG line
0   1   0    Self Test
0   1   1    Self Test
1   0   0    Master in PDIAG mode using DASP to check for Slave
1   0   1    Master in 40/80A Mode using DASP to check for Slave
1   1   0    Master in PDIAG mode using SP to check for Slave without
             checking DASP
1   1   1    Master in 40/80A mode using SP to check for Slave without
             checking DASP


======================================================================
* While my Spec form marked the jumper name DM, it is labeled as CS on
  my LPS 240AT drive.

Quantum LPS540A:
1120 cyl.    16 hds.     59 sec/trck    541MB
1024 cyl.    16 hds.     63 sec/trck    528MB

The second option is for those that will use the drive under DOS (1024 limit
without driver support).

9-12ms avg. access time
ECC Reed Solomon, 4,500 rpm, local bus support, fast multiword DMA, 128k cache
(of this 32k is used by firmware), read/write caching.


The QUANTUM ELS series:

Model       Cap     Avg Acc     Cylinders     Heads    Sectors/Track
            (MB)     (ms)
 
ELS42AT        42        -           968          5             17
ELS85AT        85        -           977          10            17
ELS127AT       127       -           919          16            17
ELS170AT       170       -           1011         15            22

Write precomp = 0 for all Quantum drives ( probably no significance)
Landing Zone = Cylinders

Straps: If an ELS drive is 
        master only, use DS
        master with slave, DS or, DS and SP in some cases
        slave, no strap


*********************   RODIME Rodime rodime   ******************************

Information for RO 3008A and RO 3009A series hard disk drives:

Drive Types

   Model        Cyls    Hds     Sectors/Trk      No. blocks     Formatted Cap.
  -------       ----    ---     -----------      ----------     --------------
  RO3058A       868      3          34             88,536        45.33 MByets
  RO3088A       868      5          34            147,560        75.55 MByets
  RO3095A       923      5          34            156,910        80.33 MByets
  RO3128A       868      7          34            206,584       105.77 MByets
  RO3135A       923      7          34            219,674       112.47 MByets
 
  RO3059A       217     15          28             91,158        46.67 MByets
  RO3089A       325     15          28            136,737        70.00 MByets
  RO3129A       492     15          28            206,645       105.80 MByets
  RO3139A       523     15          28            219,735       112.50 MByets
  RO3209A       759     15          28            319,053       163.35 MByets
  RO3259A       976     15          28            410,211       210.02 MByets


Link Options

   In order to install the Rodime Ro 3000A series drives the dumpers for 
the single/dual drive and LED operation on the drive need to be set as 
described in the relevant product specification.
   I a single drive environment the drive is described as a Master.
   In a dual drive environment the drives are described as a Master and a
Slave. This is due to the protocal the takes place between the two drives 
when performing diagnostics.
   There are four links, LK1, LK2, LK4 and LK5, adjacent to the 40 way 
interface connector. They have the following functions and are described 
in order as viewed from the end of the drive, with the first jumper 
described nearest the 40 way interface connector.

LK2: LED 
     When fitted, this jumper connects the LED drive to pin 39 of the
     interface. This allows a LED to be connected to the interface. An
     external current limiting resistor needs to be fitted in series with
     the LED when this option is selected. The value of the resistor will
     be dependant on the LED type chosen but will be in the range of 130
     Ohms ot 220 Ohms.

LK1: Dual Drives
     This jumper must be fitted when two drives are attached to a single
     bus. It fallows communication across the 40 way interface connector,
     indicating, to the Master drive, the presence of a Slave.

LK4: Master
     When fitted this signifies that the drive jumpered is a Master. If
     there are two drives connected on a single bus then only one may be
     jumpered in this way.

LK5: IOChRdy
     When fitted this connects the IOChRdy signal to the drive, it is 
     fitted when the drive is used in host systems that have a higher
     data transfer rate than the drive i.e. greater than 4 MBytes per
     second when using 1:1 interleave. This jumper is not normally 
     fitted as most hosts transfer at a lower rate than 4 MBytes per
     second.

   There are four possible Master/Slave configurations in which a drive(s)
may be jumpered:

     Master, single drive with LED on interface         LK2 & LK4 fitted.
     Master, single drive without LED on interface      LK4 only fitted.
     Master, dual drive without LED on interface        LK4 & LK1 fitted.
     Slave, dual drive without LED on interface         No jumpers fitted.
     Master, dual drive with LED on interface           LK4, LK1 & LK2 fitted.
     Slave, dual drive with LED on interface            LK2 only fitted.

   The Master drive will delay power-up for approximately two seconds to
reduce power surges in applications where dual drives are used.

   The other connections for a LED will be found close to the 28 way 
connector at the other end of the drive. This LED driver is not affected
by the link options. An internal current limiting resistor is on the 
drive for this LED driver. Refer to the product specification for further
details.


*************************** SAMSUNG Samsung samsung  *************************

            CYL   hd  Sectors
SHD-3101A   776    8    33        (100 MB)  (MB = 1024 bytes)
SHD-3061A   977    7    17        (56.76 MB)
SHD-3062A   917   15    17        (114 MB)

for drive SHD-3101A, SHD-3061A and SHD-3062A

                             2 drives
Jumper     1 drive      Master       Slave
C/D           J           J            NJ
DSP          NJ           J            NJ
ACT           J          (1)           (1)
HSP          NJ          NJ            (2)
                       J = Jumpered
                      NJ = No Jumpered

(1) In a two-drive system,it is possible to drive one LED
    with both drives. An external current limiting resister is required

(2) If the drive is connected to a host that requires that the - DIRVE SLAVE
    PRESENT be supplied from the slave drive via the interface signal -
    HOST SLV/ACT, then this jumper must be installed, the ACT jumper must
    not be installed because the two jumpers are mutually exclusive



***************************  SEAGATE Seagate seagate  *************************

There is a list of most Seagate HD (including MFM, SCSI, ESDIand IDE) on
every Simtel mirror under

/msdos/dskutl/1seagate.zip

It contains info about the following drives:

            st1144a     st138a      st274a      st3283a
st1057a     st1156a     st1400a     st280a      st351ax
st1090a     st1162a     st1401a     st3051a     st9051a
st1102a     st1186a     st1480a     st3096a     st9077a
st1111a     st1201a     st157a      st3120a     st9096a
st1126a     st1239a     st2274a     st3144a     st9144a
st1133a     st125a      st2383a     st325ax

additional info:

ST3243A     204 MB      Cyl/Hd/spt  1024/12/34
ST351AX     41  MB                  820/6/17
ST9235A     200 MB                  985/13/32

and also...

pd1:<msdos.info>        (on SIMTEL mirrors)
1SGATHTX.ZIP    Seagate tech support's disk ref (needs HHV20)

This is a concise and complete source of information for all hard disks
that Seagate makes, including MFM, RLL, IDE, and SCSI types.  This
information includes:

        Detailed technical specifications for each drive
        Switch and Jumper settings for each drive (more than just settings
                for BIOSs and low--level formatting routines)
        Miscellaneous notes about each drive

This is the most up-to-date information that Seagate provides on its BBS.
It is dated 05/14/93.

This file is a hypertext version of file 1SEAGATE.ZIP and requires
HHV20.ZIP to view it.


*******************   TEAC Teac teac  ********************

Model: SD-3105

                Cyls.   Heads   Sect/T  PreCmp  LZone   Capacity
                ------  ------  ------  ------  ------  ---------
Physical         1282       4      40       -       -   105021440
BIOS (AMI)        641       8      40       0       0   105021440 (100.2M)
     (Award)      926      13      17       0       0   104778752  (99.9M)
     (Phoenix)    776       8      33       0       0   104890368 (100.0M)

Connectors and Jumpers:

   +----+                    1           Jumper  Function
   |....| +---+ +-------/ /---+   2 0       0    ON:  -ACT selected (ext.LED)
   |    | |...| |::::::/ /::::|  ::::            OFF: -SLV PRESENT selected
   +----+ +---+ +-----/ /-----+  3 1        1    ON:  Two HDD's
     J2     J7  40    J1         ----            OFF: Single HDD
   Power (Power)    Signal      Jumpers     2    ON:  Master (/Single)
                                                 OFF: Slave (with 2 units used)
                                            3    ON:  -I/O CH RDY not output
                                                 OFF: -I/O CH RDY is output
Master Slave Settings:

Jumper no.:   1     2
-----------------------
Single....:   0     1                            1, ON  = jumpered
Master....:   1     1                            0, OFF = not jumpered
Slave.....:   1     0


*********************   TOSHIBA Toshiba toshiba   ***************************

                    cap     Cyl     Hd      spt
MK1122FC            41      977     2       43
MK2024FC            82      977     4       43
MK2124FC            124     934     16      17
MK2224FC            203     684     16      38
MK234FCH            101     845     7       35

Toshiba MK 234FCF.  
        845     Cyl
        7       Head
        0       Pre
        845     LZ
        35      Sectors
        101     Size
The jumpers settings I got from Toshiba.  They refer to 
connector PJ10, the 1st being the pair of pins closet to the
outside of the drive and the 6th being the pair closest to
center of the drive.  
        configuration           jumpers on
        ------------            ----------
        single drive            1st and 3rd
        master w/ slave         1st, 3rd, and 4th
        slave                   1st


**************** WESTERN DIGITAL Western Digital western digital **************

Caviar series:

Name        Size (Mb)    Cylinders   Heads   Sectors
----------------------------------------------------
WDAC140      40.7         980            5        17
WDAC280      81.3         980           10        17
WDAC1170    163          1010            6        55
WDAC2120    119.0        1024           14        17
WDAC2170    162.7        1010            6        55
WDAC2200    202.8         989           12        35
WDAC2250    244          1010            9        55
WDAC2340    325.4        1010           12        55
WDAC2420    405.6         989           15        56


> My 1st HD was a Quantum (LPS) 105AT (I assume th LPS, as I haven't any 
> docs.) 
> >LPS 105AT   105       17           755         16            17
> The second was a Western Digital Caviar 340Mb:
> >WDAC2340    325.4        1010           12        55
> Using the information from your document, I set up the Quantum as master
> and the WDC as slave. This worked fine most of the time, but when booting
> sometimes HDD-controller errors occured. When I switched the drives (WDC
> as master, Quantum as slave) it worked perfectly, as has done ever since.

Manufacturer: Western Digital
Serie:        Caviar
Name:         WDAC2420
Size(Mb):     405.6
Cylinders:    989
Heads:        15
Sectors:      56
(uses dynamic translation)
Jumpers:      CP MA SL

The drive runs as a slave with a WDAC2200 as master just fine.


Please note that these are the *recommended* CMOS parameters. All the disks 
support so-called dynamic translation, and should thus be able to work with
any parameters having fewer sectors than the total number of sectors on
the disk.

Now, according to the manual, the jumper settings are as follows:

Jumper                               CP   MA   SL
-------------------------------------------------
Single                                0    0    0
Master                                0    1    0
Slave                                 0    0    1
Slave with Conner CP342 or CP3022     1    0    1   


Maybe there are 2 kinds of Caviar's floating around: 

If your jumpers read MA SL and SI then use:
Jumper  SI      MA      SL
Single  1       0       0
Master  0       1       0
Slave   0       0       1

There have been reported difficulties in using WD Caviar as Master and
NEC drives as slave - the other way it works.
> When I installed a Conner CP3204F (203 MB) as master and a WD Caviar 2200
> (203 MB) as slave, both with and without the "CP" jumper, the Caviar had
> seemingly normal behaviour. However, when doing writes to the Caviar, once
> in a while it would overwrite directories etc. Using FASTBACK was almost
> impossible.
> 
> The workaround is to install the Caviar as the master, and the Conner
> as the slave.


> I had a WD pirana 4200 (212 mb) IDE drive and added a Caviar 2340 (341 mb)
> drive.  No matter what I did with the CMOS settings, as soon as I define
> the D drive (as anything) and rebooted, it would hang for about 2 minutes
> and then report "D: drive failure".  I am using an intelligent IDE controller
> since my AMI bios was too old to support IDE drives.
> 
> The fix was to call the 4200 the slave and the 2340 the master.
> All has been working fine since then.


WD93044-A  (40 MB)
BIOS-Settings 
977 cyln, 5 heads, 17 sect, LZone: 977 

+-------+ +---+---+---+  1: drive is master
| cable | | 1 | 2 | 3 |  2: drive is slave
+-------+ +---+---+---+  3: second drive is a conner-drive

No jumper set: this is the only drive.

--

WD93048-A
40 MB
Cyl 782
Heads 4
s/track 27

Jumper not known; try settings for WD93044-A

--

WDAH260     60MB    Cyl/Hd/spt      1024 7 17
WDAH280     82MB                    980 10 17

WDAP4200    202MB                   987 12 35



********************  Useful telephone numbers...  ********************

Conner:
  BBS: 408-456-4415
  Talk info: 1-800-426-6637
  FaxBack: 408-456-4903

The "Talk info" number above is now a Fax-on-demand system.  Very nice,
considering both the incoming call and outgoing fax are paid for by them!
You can also speak with a human for technical assistance at this number.

        (Conner Europe (in UK)  ;  +44 628 777277 (voice)
                                   +44 628 592801 (fax))
Miniscribe:     
  303-651-6000

Maxtor:
  Info/tech support: 800-262-9867
  FAX-back: 303-678-2618
  BBS: 303-678-2222
  They list their 800 number as 1(800)2-MAXTOR.

Quantum:
  408-894-4000
  408-944-0410 (Support)
  408-894-3218 (FAX)
  408-894-3214 (BBS)

Seagate:
  Info/tech support: 408-438-8222
  FAX-back: 408-438-2620
  BBS: 408-438-8771

Western Digital:
  Info/tech support: 714-932-4900
  BBS:
  U.S. 1200/2400    714-753-1234
  U.S. 9600         714-753-1068
  France 1200/2400  ..-331-69-85-3914 (? French code is 33 not 331)
  Germany 1200/2400 ..-49-89-922006-60
  U.K.  1200/2400   ..-44-372-360387

The US Toll free number for Western Digital tech support is
800-832-4778


*******************   last but not least   *****************

If I could help you with my little collection and if you live in a
part of the world far away from me, how about a postcard for my pinboard?
I will surely answer!

Carsten Grammes                 
Saarbruecker Str. 47
D-66292 Riegelsberg
Germany

S) 5.0 >Video

This section is posted separately as the "comp.sys.ibm.pc.hardware.video
FAQ" and "comp.sys.ibm.pc.hardware.video Chipsets List" and archived
along side this FAQ.  Refer to section one for instructions on
retrieving these files.

Newsgroups: comp.sys.ibm.pc.hardware.video
Subject: comp.sys.ibm.pc.hardware.video FAQ, Part * / *
From: scott@bme.ri.ccf.org (Michael Scott)
Summary: This is a monthly posting containing a list of Frequently
         Asked Questions (and their answers) pertaining to video
         hardware for IBM PC clones.  It should be read by anyone who
         wishes to post to the comp.sys.ibm.pc.hardware.video
         newsgroup.
Archive-name: pc-hardware-faq/video/part*
URL: http://www.heartlab.rri.uwo.ca/videofaq.html
                                ---
Newsgroups: comp.sys.ibm.pc.hardware.video
Subject: comp.sys.ibm.pc.hardware.video Chipsets List
From: scott@bme.ri.ccf.org (Michael Scott)
Summary: This document is distributed with the comp.sys.ibm.pc.hardware.video
         FAQ and contains information on video chipsets and specific video
         card models.
Archive-name: pc-hardware-faq/video/chipsets
URL: http://www.heartlab.rri.uwo.ca/videofaq.html
 
S) 6.0 Systems

Q) 6.1  *What should I upgrade first?

Q) 6.2  Do I need a CPU fan / heat sink

[From: jruchak@mtmis1.mis.semi.harris.com (John Anthony Ruchak)]

This is highly debatable.  In general, if you buy from a good,
self-respecting company, any additional cooling requirements would
have been taken care of before your system was delivered to you.
 
I'm responsible for PC maintenance at my site, and I don't worry about
additional cooling in any of the pre-packaged systems we receive.  All
rebuilt and/or upgraded 486-33 (or higher) systems do, however,
receive additional cooling because older cases may not provide
adequate ventilation for today's technology.  Additional cooling on
the infamously-hot Pentium (586) is always added.

So, do YOU need a CPU fan in YOUR system?  Probably not for "ready to
run out of the box systems."  If you are _REALLY_ worried that your
system is suffering from too much heat, consult with a reputable
service center.  They will not only answer your questions, but they
can also install any additional cooling systems that may be needed.  A
good rule of thumb, though - "don't try to fix what isn't broken."
In other words, if your system is working, don't look for trouble.

Q) 6.3  What does the turbo switch do?

[From: cls@truffula.sj.ca.us (Cameron L. Spitzer)]

It slows your system down so you can play games that were written
with timing mechanisms based on CPU execution rate.  I know of three
implementations:
1.  A programmable divider delivers the clock signal at two different
    speeds.
2.  Extra wait states are inserted in all memory cycles.
3.  Dummy DMA cycles or extra referesh cycles are inserted.
The first is by far the most common.

Q) 6.4  How does the front panel LED display measure the system's speed?

It doesn't.  The only useful information going to these displays is if
you are in turbo mode.  They have jumpers or dials behind the display
which you can use to set them to show any two arbitrary numbers (for
turbo and non-turbo modes).

Q) 6.5  Should I turn my computer/monitor off?

Turning a device on/off causes thermal stress.  Leaving it on causes
wear and tear (even on non moving parts).  The only thing you
shouldn't do is quickly power cycle the computer.  If you turn it
on/off, leave it that way for at least a few seconds.  Other than
that, it's up to you.

Q) 6.6  Are there any manufacturers/distributers who read the net?

Yes, it is known that Zeos, Gateway 2000, Dell, Adaptec, HP and others
all read the net to some extent.  However, for best results, use the
support phone numbers.


===============
Ralph Valentino (ralf@fs09.webo.dg.com) (ralf@wpi.edu)
Senior Hardware Engineer, AViiON System Development
Data General Corporation, Westboro, MA USA