SGI Developer Toolbox 6.1/SGI Developer Toolbox 6.1 - Disc 4.iso/FAQs/netfaqs/SCSI-faq

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Newsgroups: comp.periphs.scsi,comp.answers,news.answers
From: [e-mail] (Gary Field)
Subject: comp.periphs.scsi FAQ part 1 of 2
Expires: Wed, 1 Jun 1994 05:00:03 GMT
Reply-To: [e-mail] (Gary Field)
Organization: Wang Labs, Lowell MA, USA
Date: Mon, 4 Apr 1994 15:20:19 GMT
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Followup-To: comp.periphs.scsi
Summary: This posting contains a list of Frequently Asked
             Questions (and their answers) about SCSI.  It
             should be read by anyone who wishes to post to the
             comp.periphs.scsi newsgroup.
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Archive-name: scsi-faq/part1


                  SCSI FAQ:
       Frequently Asked Questions for comp.periphs.scsi

                  VOLUME I

FAQ history:    Created by Johnathan Vail ([e-mail]) from articles
        submitted to him by comp.periph.scsi readers.
        Maintained by Johnathan Vail until November 1993.

Current Editor: Gary Field ([e-mail])

Last Modified: Apr 04, 1994

Master Table of contents:

Part 1
    What is SCSI ?
    Is it possible for two computers to access the same SCSI disks?
    What is the problem with the Adaptec 1542C and external cables?
    Where can I get SCSICNTL.EXE and other Adaptec files?
    What is the difference between the Adaptec 1542A and 1542B?
    What are the differences between the Adaptec 1542B and the 1542C?
    What are the differences between the 1542C and the 1542CF?
    What kinds of Optical Drives are available?
    Where can I get FTP/download SCSI documents?
    Where can I get SCSI documents?
    Where can I get information on various disk drives and controllers?
    What is the telephone number of Adaptec?
    What is the telephone number of Archive Corporation?
    What is the address and telephone number for Quantum?
    What is the telephone number for Seagate?
    What is the telephone number and address of Conner Peripherals?
    What is the number for NCR?
    What is the address and telephone number of UltraStor?
    What is the address and telephone number of Wangtek?
    What is the address and telephone number of Western Digital?
    What is FAST SCSI?
    SCSI terminators should measure 136 ohms?
    Can someone explain the difference between 'normal' and differential scsi?
    What are the pinouts for differential SCSI?
    What are the pinouts for SCSI connectors?

Part 2
    What is the difference between SCSI-1 and SCSI-2?
    Is SYNCHRONOUS faster than ASYNCHRONOUS?
    Is the 53C90 Faster than spec?
    What are the jumpers on my Conner drive?
    What are the jumpers for my Wangtek 5150 drive?
    What is CAM?
    What is FPT (Termination)?
    What is Active Termination?
    Why Is Active Termination Better?
    Why is SCSI more expensive than IDE?
    What is Plug and Play SCSI?
    Where can I get drivers (ASPI and other) for the WD7000 FASST2 host adapter?

====
QUESTION: What is SCSI?
ANSWER From: LSD, L.J.Sak@Kub. Edited by Gary Field
====

SCSI stands for Small Computer Systems Interface. It's a standard for
connecting peripherals to your computer via a standard hardware interface,
which uses standard SCSI commands. The SCSI standard can be divided into
SCSI (SCSI1) and SCSI2 (SCSI wide and SCSI wide and fast).
SCSI2 is the most recent version of the SCSI command specification and
allows for scanners, hard disk drives, CD-ROM players, tapes [and many other
devices] to connect.
SCSI is becoming a popular standard. More and more computers use it daily.
(e.g. ATARI Falcon and TT, expensive MS-PC's, Amiga, Apples and many others)


====
QUESTION: Is it possible for two computers to access the same SCSI disks?
ANSWER From: [e-mail] (Michael Burke)
====

Yes, two (or more) systems can be on the same scsi bus as scsi disk and
tape drives. As long as the scsi requirements are met - cable lengths,
termination and type - the devices can share the scsi bus.

The question should be - Are there any O/S' that will allow the sharing of
file systems? It would not make sense for two hosts to go about treating
shared disks as if they owned the device. Data would be destroyed pretty
quickly.

On the issue of tape devices, however, O/S' tend to give exclusive usage
to an application. In this way, tape drives can be shared much more easily.

Disks can be best shared by having two (or more) partitions on a disk. Each
host "owning" its own file system.



====
QUESTION: What is the problem with the Adaptec 1542C and external cables?
ANSWER From: Scot Stelter, Adaptec  (Product Manager for the AHA-1540)
====

Several articles lately have cited the importance of SCSI-2-compliant
cables when cabling SCSI bus subsystems.  Perhaps the most accurate
and technically detailed one was published in Computer Technology
Review in March (Volume XIII, No. 3. PP. 6).  In short, it explains
the double-clocking mechanism that can occur due to cables whose
impedance falls below the 90-Ohm SCSI-2 spec.  Steep edge speeds on
the REQ and ACK lines of the SCSI bus exacerbate the problem, but
non-compliant cables are the root cause. Both LAN TIMES in the US
(5/24/93, page 115) and CT Magazine in Germany (7/93, page 18) cite
this cable problem.

In an extensive survey of cables available in the US and Europe, we
found that more than half of the cables available have single-ended
impedances in the 65 to 80 Ohm range -- below the 90 to 132 Ohms
specified in the SCSI-2 spec.  It seems that some (not all) cable
vendors do not understand the specification, describing their cables
as SCSI-2 compliant when they are not.  A common misconception is that
SCSI-2 means a high-density connector.  In fact, there are several
connector options.  I have published a technical bulletin that
summarizes the critical requirements (TB 001, April 1993). An artifact
of its faster design left the AHA-1540C with faster edge-speeds than
its predecessor, the AHA-1540B.  As I have said, this can exacerbate
the effect of bad cables.  This explains why some users could get
their AHA-1540B to work when an early AHA-1540C might not.
Essentially, the 1540B was more forgiving than the early 1540Cs.  Good
cables fixed the problem, but unfortunately for the user, good cables
are hard to find.

After surveying the cable market and many of our customers, we decided
that bad cables were going to be here for a while, and we had to make
the 1540C as forgiving as the 1540B was.  At the end of April we made
a change to the AHA-1540C that involved using a passive filter to
reduce the slew rate of the ACK line, the signal that the host adapter
drives during normal data transfers.  Extensive testing with many
intentionally illegal configurations confirms that we succeeded. Prior
to release, we tested the AHA-1540C with over 200 peripherals, systems
and demanding software programs with no failures.  Then, a second team
retested the AHA-1540C across a wild combination of temperatures,
humidities and other stresses.  This testing gives me confidence that
the AHA-1540 line continues to serve as the gold standard for SCSI
compatibility.


====
QUESTION: What is the difference between the Adaptec 1542A and 1542B?
ANSWER From: [e-mail] (Harvey Fishman)
====

The AHA-1542A is obsolete and no longer supported by Adaptec.  They
stopped providing firmware upgrades at some level prior to the equivalence
to the 3.10 level of the AHA-1542B firmware.  I am not sure just where
though.  The present latest AHA-1542B firmware is version 3.20, and
supports drives up to 8GB under MS-DOS.


====
QUESTION: What are the differences between the Adaptec 1542B and the 1542C?
ANSWER from: Terry Kennedy ([e-mail])
====

The 1542C is an an updated model which replaces the 1542B. The 1542C features
jumperless setup, having only 8 DIP switches. All other configuration options
are set using the 1542C's built-in BIOS configuration utility. Configurable
features not found on the 1542B are:

  o Ability to enable/disable sync negotiation on a per-ID basis (the 1542B
    could only do it for all ID's on the SCSI bus)
  o Ability to send "start unit" commands on a per-ID basis
  o BIOS works with alternate I/O port settings on the adapter
  o Ability to boot from ID's other than 0
  o Software-selectable termination
  o Software-selectable geometry translation
  o Additional DMA speeds of 3.3 and 10 MB/sec

Additionally, the 1542C uses a Z80 CPU and 8Kb buffer instead of an 8085 and
2Kb buffer as on the 1542B.


====
QUESTION: What are the differences between the 1542C and the 1542CF?
ANSWER from: Terry Kennedy ([e-mail])
====

The 1542CF includes all of the 1542C features, and adds "Fast" SCSI operation,
providing SCSI data rates of up to 10MB/sec (compared with an upper limit of
5MB/sec on the 1542C). This is unrelated to the host DMA rate. It also has a
software-configurable address for the floppy controller and a "self-healing"
fuse for termination power.


====
QUESTION: Where can I get SCSICNTL.EXE and other Adaptec files?
ANSWER From: [e-mail] (Randy Bush)
        and  Timothy Hu [e-mail]
====

New files from Roy as follows:

ftp.psg.com:~/pub/adaptec/...

-rw-rw-r--  1 randy    staff      110689 Feb 25 00:29 SCSICNTL.EXE.Z
-rw-rw-r--  1 randy    staff      368640 Feb 25 00:27 adse.dd
-rw-rw-r--  1 randy    staff        1959 Feb 25 00:25 adse.dd.readme
-rw-rw-r--  1 randy    staff       17896 Feb 25 00:37 list
-rw-rw-r--  1 randy    staff       99545 Feb 25 00:20 os2drv.zip
-rw-rw-r--  1 randy    staff       70801 Feb 25 00:20 scsi_drv.Z
-rw-rw-r--  1 randy    staff       66508 Feb 25 00:24 scsi_drv.readm
-rw-rw-r--  1 randy    staff      118697 Feb 25 00:17 update.pkg.Z


You can get the ASPI specs from Adaptec's Bulletin Board [phone].


====
QUESTION: What kinds of Optical Drives are available?
ANSWER From: [e-mail] (John Kim)
====

As I promised I am posting the summary of what I learned about 128mb optical
drives through many kind replies and some effort on my part. The purpose of
this informal survey was to aid people (starting from myself) in deciding on
which 128mb optical drive to buy.

When I posted my questions, it was done only on comp.mac.sys.hardware and
forgot to do the same also on comp.arch.storage and comp.periphs.scsi where
are less traffic than c.m.s.h. However, as a Macintosh owner myself, this
survey was biased toward the Mac world and the mail order houses mentioned
specializes in Mac-related products, although the below mentioned optical
drives might be usable also with non-Mac platforms (Sun, NeXT,
PC-compatibles).

My questions were:

o what kind of drive you bought from whom at what price
o what drive mechanism (MOST, Epson, Fujitsu, Sony, ...) it uses
o how fast it is in terms of average seek time & data transfer rate
o how noisy the drive is
o how large and heavy the drive is
o what drive formatting program (eg, FWB or Silver Lining) you use what its
  goods/bads
o the quality of the service of the seller (mail order company, retail store,
  etc.)


Summary

In general, these days, some magneto-optical (MO) drives seem to be
almost as fast as (if not faster than) ordinary hard drives (HD). The
access time of fastest 128MB MO drives (around 30ms) are slower than
average HD's access time (15ms) but the transfer rate seems to be
about the same (764KBytes/sec) or not much slower. The advantages of
the MO drives over the HDs are that your storage space is almost
limitless, expandable at a relatively cheap price ($40/120MB = 34
cents/MB) compared to $1/MB rate of HDs or that of SyQuest drives, and
the life of the media is very long (they say it's 30 years or
rewritable 100,000 times.)

Fijitsu 128 REM Portable: At this moment, to my knowledge, 128 MByte
optical drives based on Fujitsu mechanism seems to be the fastest,
roughly having average seek time of 30ms and average transfer rate of
768KBytes/sec. Another good thing about this Fujitsu drive is that it
is more compact in size than previous 128mb optical drives, ie,
"portable". I don't know how Fujitsu mechanism (FM) is different from
Epson mechanism (EM) and how FM provides a similar performance at a
cheaper price in a smaller frame. Maybe using split-head
implementation to make the read-write head lighter? Could anybody post
info on this? One person tells me that the eject mechanism is too
strong, sometimes shooting the cartridge out making them land on the
floor. He says Fujitsu told him that the FM's coming out in April will
have gentler eject.

Epson: The next fastest (or maybe just about the same speed) are Epson
mechanism (EM) drives, having average access time of 34ms and transfer rate of
768KB/sec.  These achieve faster speed compared to other old mechanisms by
having a higher rpm (3600rpm vs. past 2400 rpm).

Slower ones: Other mechanisms (Sony, Panasonic, etc.) seem to have
been dominating the optical drive market before FM and EM's advent.
These have a typical access rate of ~45ms.  I don't know if now there
are new implementations that make them perform better then FM and EM.
Maybe someone can tell us.

Noise Level: One thing to consider might be noise of the drive. Different
mechanisms may have typical noise level, but one thing sure is that different
resellers/companys' drive's noise level differs even for the same drive
mechanism, eg, Sony. It looks like different casing produces different noise
levels? (Could someone confirm/disconfirm this aspect?)  Base on the report
in Nov '92 issue of MacWorld, the noise level of MacDirect, MacProduct and
DGR 128mb MO drives seem to be OK or quite quiet.

This issue of MacWorld deals with removable media drives (optical drives of
various capacity, SyQuest, Bernoulli and Flopticals) and you can get some
idea on what the differences among different drive mechanisms are.

Formatting Software: Another thing to consider is what kind of media
formatting software you will use. All companys (or mail order places) seemed
to provide for free formatting program with their drives. I don't have the
details on this. But an inefficient formatting can result in slow drive
performance. The most popular one used to be FWB's Hard Disk Toolkit but
Anubis (advertised to improve performance up to 35% [compared to what?]) is
beginning to be used also. I don't know if all formatting program and the
drive hardware allows to have read and write verify off but by having these
turned off you can obtain significant speed boost at the risk of less secure
data transfer. MacWorld's report warned that drives from some companys don't
let you turn on/off the verify. In the worst case, some come with verify off
and no option to toggle it back to ON.

256mb MO drives: In general these have better transfer rate (1.23MB/sec) and
a little slower access time (35ms). I feel that this capacity will soon be
the next standard. These drives are able to also read/write 128mb cartridges
and 256mb will soon be new ANSI and ISO standard. I once heard from a
saleperson at a mail order place that these are not reliable yet and he saw
many they sold came back with complaints. This may be a non-general instance
on a typical drive mechanism (seems to be MOST mechanism). Personally, I feel
128mb is accomodating enough for personal usage at home unless you are
dealing with very large data files (eg, large graphic images).




====
QUESTION: Where can I get FTP/download SCSI documents?
ANSWER From: [e-mail] (News Administator)
====


Last Changed:    Thu Sep 24 23:31:09 CDT 1992 (New BBS Phone number)

This is a periodic posting of information about some of the archives at
ftp.cs.tulane.edu and the available files from the SCSI-BBS, including
SCSI, ESDI, IPI, and Fiber Channel documents from the standards committees.

These files are available for FTP from ftp.cs.tulane.edu in the directory
pub/scsi. Files are stored in file areas as they are found in the BBS with
each area having a file named 'files.bbs' that tells what each file is. The
file pub/scsi/index.Z list each file area, its descriptions and its files.

Thanks to John Lohmeyer of NCR, a majority of the SCSI related files from the
SCSI BBS are now available for anonymous ftp. These files were sent to me by
Mr. Lohmeyer at his expense so that more people would have access to them.
The SCSI BBS (719-574-0424) contains a large amount of data relating to SCSI,
and ESDI as well as SCSI-2, IPI, and Fiber Channel, as well as the last
revision of the SCSI-1 standard before it went to publication by ANSI.

Most of the files in the SCSI archive are either archived with the ZIP utility
or compressed with the 'compress' program. Most of the text files are stored
as Wordstar word processing files. PKzip for PC/MS-DOS is included in the
archive to allow users to break up the .ZIP files, and the PC/MS-DOS binaries
and .C source are also in the archive to convert the Wordstar documents to
ASCII text.

[Added by Gary Field Dec 21,1993]
There is also a lot of good information at ncrinfo.ncr.com



====
QUESTION: Where can I get SCSI documents?
ANSWER #1 From: [e-mail] (Kevin Jones)
         and [e-mail] (John Matrow
====

The only literature that I'm aware of is:

  The SCSI specification: Available from:

      Global Engineering Documents
      15 Inverness Way East
      Englewood Co  80112-5704
      [phone]
    SCSI-1: X3.131-1986
    SCSI-2: X3.131-199x
    SCSI-3 X3T9.2/91-010R4 Working Draft

(Global Engineering Documentation in Irvine, CA [phone]??)


SCSI-1: Doc # X3.131-1986 from ANSI, 1430 Broadway, NY, NY 10018


IN-DEPTH EXPLORATION OF SCSI can be obtained from
Solution Technology, Attn: SCSI Publications, POB 104, Boulder Creek,
CA 95006, [phone], FAX [phone]

THE SCSI ENCYLOPEDIA and the SCSI BENCH REFERENCE can be obtained from
ENDL Publishing, 14426 Black Walnut Ct., Saratoga, CA 95090,
[phone], FAX [phone]

SCSI: UNDERSTANDING THE SMALL COMPUTER SYSTEM INTERFACE was published
by Prentice-Hall, ISBN 0-13-796855-8 (Seems to be out of print)


ANSWER #2 From: Gary Field ([e-mail])

A neat little book called "Basics of SCSI" second edition, was sent to me
free of charge by Ancot Corporation, Menlo Park, CA [phone].
It gives a simplified description of how most aspects of the SCSI bus work
and includes some discussion of SCSI-2 issues.

ANSWER #3 From: Runar Jorgensen ([e-mail])

There was a two part article in Byte Magazine. The first part was in Feb 1990
issue, p. 267-274 and the second was in Mar 1990 issue, p. 291-298.
Another two part article appeared in Byte in May 1986 and June 1986.

====
QUESTION: Where can I get information on various disk drives and controllers?
ANSWER: [e-mail] (Eric Krieger) (Updated Nov. 29, 1993)
====

        Drive and Controller Guide,  Version 4.3

   THEREF(tm) is a comprehensive Directory of Hard Drives, Floppy Drives,
Optical Drives, and Drive Controllers & Host Adapters.  It is designed to
help the novice and pro alike with integration problems and system setups.

   Information is provided in two handy formats; Portrait mode, for those
who prefer a normal book-binding type print format, and(or) do not have a
printer with Landscape capability.  And Landscape mode, for those who pre-
fer a computer-printout type format.

   For printing, a Laserjet is preferred, but not necessary, and setup
info is provided.  For viewing, LIST(tm) by Vernon Buerg, will provide an
excellent result, and allow text searches for finding specific models.

By F. Robert Falbo


The archive is available at the following sites, all members of AmiNet
(list valid in November '93):

USA (MO)     ftp.wustl.edu           128.252.135.4   pub/aminet/
USA (TX)     ftp.etsu.edu            192.43.199.20   pub/aminet/
USA (CA)     ftp.cdrom.com           192.153.46.2    pub/aminet/
Scandinavia  ftp.luth.se             130.240.18.2    pub/aminet/
Germany      ftp.uni-kl.de           131.246.9.95    pub/aminet/
Germany      ftp.uni-erlangen.de     131.188.1.43    pub/aminet/
Germany      ftp.cs.tu-berlin.de     130.149.17.7    pub/aminet/
Germany      ftp.th-darmstadt.de     130.83.55.75    pub/aminet/
Germany      ftp.uni-paderborn.de    131.234.2.32    pub/aminet/
Germany      ftp.uni-oldenburg.de    134.106.40.9    pub/aminet/
Switzerland  ftp.eunet.ch            changing        pub/aminet/
Switzerland  litamiga.epfl.ch        128.178.151.32  pub/aminet/ (*)
UK           src.doc.ic.ac.uk        146.169.2.1     pub/aminet/
Australia    splat.aarnet.edu.au     192.107.107.6   pub/aminet/ (*)
   (*) closed 6:30am to 4pm weekdays


The archive is present at:

pub/aminet/text/docs/TheRef43.lha    [197 K]
pub/aminet/text/docs/TheRef43.readme


Note:  When extracting the archive on non-Amiga machines (i.e.
       MS-DOS with LHA213, etc.) please use the option -a0 to disable
       the preservation of the file-attributes (otherwise LHA will
       skip the files inside the archive with the message "special
       attributes").


The file is also on ftp.funet.fi:

pub/doc/disks/TheRef43.lha.2         [197 K]
pub/doc/disks/TheRef43.readme.2


====
QUESTION: What is the telephone number of Adaptec?
ANSWER From: [e-mail] (Jon D Caples)
====

    408 945-8600    Main number
    800 959 7274    tech support
    800 442 7274    orders doc, new bios, etc.

    Adaptec's general inquiry number, 800-959-7274, affords access
    to a FAX-based information retrieval system.  In order to
    preserve the accuracy of this information, I won't go into details
    about how to use it (since Adaptec may change things without telling
    me :).

    For those outside the CAN-US area, or local to Adaptec the direct
    FAX info number is [phone].

    There are three general topics as of this writing:

        General Information
        Sales Information
        Technical Information

    Give it a call and request the directory!  As of this writing
    there are over 130 documents available.  You need a touchtone phone
    and the fax number.  You'll also be asked for an extension number to
    stamp on the FAX which will be used to identify the recipient.



====
QUESTION: What is the telephone number of Archive Corporation?
ANSWER From: [e-mail] (Jim Pritchett)
====
Archive Corporation          [phone]
     Tech Support            [phone]
    FAX             [phone]



====
QUESTION: What is the address and telephone number for Quantum?
ANSWER From: [e-mail] (Kevin Martinez)
====

Quantum Corporation
500 McCarthy Blvd.
Milpitas, CA
95035

Technical Support Telephone Numbers:

800 826-8022   Main Technical Support Number
408 894-3282   Technical Support Fax
408 894-3214   Technical Support BBS V.32 8N1
408 434-9262   Technical Support for Plus Development Products
408 894-4000   Main Quantum Phone number




====
QUESTION: What is the telephone number for Seagate?
ANSWER From: [e-mail] (Hale Landis)
====

Here are the numbers for Seagate's Technical Support.

SeaBOARD - Bulletin Board System available 24 hours.  Use 8 data
           bits, no parity, 1 stop bit (8-N-1).

   USA/Canada  408-438-8771    9600 baud*
   England     44-62-847-8011  9600 baud*
   Germany     49-89-140-9331  2400 baud*
   Singapore   65-292-6973     9600 baud*
   Australia   61-2-756-2359   9600 baud*

   * - Maximum baud rate supported.

SeaFAX 408-438-2620

   Use a touch-tone phone to have information returned to you via
   FAX.  Available 24 hours.

Technical Support Fax [phone]

   FAX your questions or comments 24 hours.  Responses are sent
   between 8:00AM and 5:00PM PST Monday through Friday.

SeaFONE 408-438-8222

   Provides recorded information 24 hours or talk to a technical
   specialist between 8:00AM to 5:00PM PST Monday through Friday.

SeaTDD 408-438-5382

   Using a Telecommunications Device for the Deaf, you can send
   questions or comments 24 hours or have a dialog with a
   technical support specialist between 8:00AM and 5:00PM PST
   Monday through Friday.



====
QUESTION: What is the telephone number and address of Conner Peripherals?
ANSWER From: [e-mail] (Eric Krieger)
====

CONNER PERIPHERALS, Incorporated        WATTS LINE:
3081 Zanker Road                          PAY LINE: [phone]
San Jose   CA  95134                      FAX LINE:
                                          BBS LINE: [phone] (V.32)
CONNER                                                  [phone]



====
QUESTION: What is the number for NCR?
ANSWER From: [e-mail] (Guy Kendall)
====

For data manuals for any NCR chips, please call 800-334-5454 or
719-630-3384.



====
QUESTION: What is the address and telephone number of UltraStor?
====

     UltraStor Corporation
     47061 Warm Springs Blvd.
     Fremont, CA 94539

     General           [phone]
     Tech. Support  [phone]
     FAX               [phone]
     BBS               [phone]



====
QUESTION: What is the address and telephone number of WANGTEK?
ANSWER From: "Terry Kennedy, Operations Mgr" <uunet!spcvxa.spc.edu!TERRY>
====

Wangtek can be reached at:

  WANGTEK Incorporated
  41 Moreland Road
  Simi Valley, CA 93065
  [phone] [voice]
  [phone] [FAX]
  [phone] [BBS]

  WANGTEK-Europe
  Unit 1A, Apollo House
  Calleva Industrial Park
  Aldermaston, Reading
  RG7 4QW England
  (44) 734-811463 [voice]
  (44) 734-816076 [FAX]
  851-848135 [telex]




====
QUESTION: What is the address and telephone number of Western Digital?
ANSWER From: uunet!whale.st.usm.edu!rniess (Rick Niess)
====

    1-714-753-1068  Western Digital
    1-714-756-8176  Western Digital
    1-714-753-1234  Western Digital
    1200/2400 baud:    714-753-1234
    9600 baud (Hayes): 714-753-1068




====
QUESTION: what is FAST SCSI?
ANSWER From: [e-mail] (Kevin Jones)
====

There are 2 handshaking modes on the SCSI bus, used for transferring data:
ASYNCHRONOUS and SYNCHRONOUS. ASYNCHRONOUS is a classic Req/Ack handshake.
SYNCHRONOUS is "sort of" Req/Ack, only it allows you to issue multiple
Req's before receiving Ack's. What this means in practice is that
SYNCHRONOUS transfers are approx 3 times faster than ASYNCHRONOUS.

SCSI1 allowed asynchronous transfers at up to 1.5 Mbytes/Sec and
synchronous transfers at up to 5.0 Mbytes/Sec.

SCSI2 had some of the timing margins "shaved" in order that faster handshaking
could occur. The result is that asynchronous transfers can run at up to
3.0 Mbytes/Sec and synchronous transfers at up to 10.0 Mbytes/Sec.
The term "FAST" is generally applied to a SCSI device which can do
syncrhonous transfers at speeds in excess of 5.0 Mbytes/Sec. This term can
only be applied to SCSI2 devices since SCSI1 didn't have the timing margins
that allow for FAST transfers.







====
QUESTION: SCSI terminators should measure 136 ohms?
ANSWER From: [e-mail] (Steve Ligett)
====

Yes, that is what you should measure.  Let's see how that is so.  The
terminator contains 18 220-ohm resistors from signals to termpower, and
18 330-ohm resistors from those signals to ground.  I've drawn that
below:

termpower--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
           |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
220 ohms-> R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R
           |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
signals -> o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o
           |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
330 ohms-> R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R
           |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ground   --+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

When you measure from any one signal to termpower, you aren't measuring
that resistor in isolation, you are measuring that resistor IN PARALLEL
with the combination of the corresponding 330 ohm resistor plus 17
220+330 ohm resistor pairs in series.  I've redrawn the schematic to
make this easier to see:

termpower--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
           |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
           |  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R <- 220 ohms
           |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
           |  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o
           |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
           |  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R  R <- 330 ohms
  220 ohms R  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
           |  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-- ground
           |  |
           |  R <-- 330 ohms
           |  /
signal ->  o-/

<our resistor><--------- other stuff that's in parallel ---------->

We're trying to measure that one resistor from a signal to termpower,
but there's a ton of other stuff in parallel.  The resistance of that
"stuff" is 330 + 550/17 ohms (the 330 ohm resistor, in series with a
parallel combination of 17 550 ohm resistors).  The general formula for
the equivalent of two resistances in parallel is r1*r2/(r1+r2).
Whipping out my trusty spreadsheet, I find that the "stuff" has a
resistance of about 362 ohms, and that in parallel with 220 ohms is
about 137 ohms.




====
QUESTION: Can someone explain to me the difference between 'normal' scsi
           and differential scsi?
ANSWER From: [e-mail] (Ralph Valentino)
====

"Normal" SCSI is also called "Single-ended" SCSI.  For each signal
that needs to be sent across the bus, there exists a wire to carry it.
With differential SCSI, for each signal that needs to be sent across
the bus, there exists a pair of wires to carry it.  The first in this
pair carries the same type of signal the single-ended SCSI carries.
The second in this pair, however, carries its logical inversion.  The
receiver takes the difference of the pair (thus the name
differential), which makes it less susceptible to noise and allows for
greater cable length.




====
QUESTION: What are the pinouts for differential SCSI?
ANSWER From: [e-mail] (Ralph Valentino)
====

                Differential SCSI Connector Pinouts

_____________________________________  _____________________________________
| SCSI  |         | MINI  |         |  | SCSI  |        | MINI  |          |
| SIGNAL| DD-50P  | MICRO | DD-50SA |  | SIGNAL| DD-50P | MICRO | DD-50SA  |
------------------------------------  -------------------------------------
| -GND  |    2    |  26   |   34    |  | (open)|    1    |   1   |    1    |
| -DB(0)|    4    |  27   |    2    |  | +DB(0)|    3    |   2   |   18    |
| -DB(1)|    6    |  28   |   19    |  | +DB(1)|    5    |   3   |   35    |
| -DB(2)|    8    |  29   |   36    |  | +DB(2)|    7    |   4   |    3    |
| -DB(3)|   10    |  30   |    4    |  | +DB(3)|    9    |   5   |   20    |
| -DB(4)|   12    |  31   |   21    |  | +DB(4)|   11    |   6   |   37    |
| -DB(5)|   14    |  32   |   38    |  | +DB(5)|   13    |   7   |    5    |
| -DB(6)|   16    |  33   |    6    |  | +DB(6)|   15    |   8   |   22    |
| -DB(7)|   18    |  34   |   23    |  | +DB(7)|   17    |   9   |   39    |
| -DB(P)|   20    |  35   |   40    |  | +DB(P)|   19    |  10   |    7    |
|  GND  |   22    |  36   |    8    |  |DIFSENS|   21    |  11   |   24    |
|  GND  |   24    |  37   |   25    |  |  GND  |   23    |  12   |   41    |
|TERMPWR|   26    |  38   |   42    |  |TERMPWR|   25    |  13   |    9    |
|  GND  |   28    |  39   |   10    |  |  GND  |   27    |  14   |   26    |
| -ATN  |   30    |  40   |   27    |  | +ATN  |   29    |  15   |   43    |
|  GND  |   32    |  41   |   44    |  |  GND  |   31    |  16   |   11    |
| -BSY  |   34    |  42   |   12    |  | +BSY  |   33    |  17   |   28    |
| -ACK  |   36    |  43   |   29    |  | +ACK  |   35    |  18   |   45    |
| -RST  |   38    |  44   |   46    |  | +RST  |   37    |  19   |   13    |
| -MSG  |   40    |  45   |   14    |  | +MSG  |   39    |  20   |   30    |
| -SEL  |   42    |  46   |   31    |  | +SEL  |   41    |  21   |   47    |
| -C/D  |   44    |  47   |   48    |  | +C/D  |   43    |  22   |   15    |
| -REQ  |   46    |  48   |   16    |  | +REQ  |   45    |  23   |   32    |
| -I/O  |   48    |  49   |   33    |  | +I/O  |   47    |  24   |   49    |
|  GND  |   50    |  50   |   50    |  |  GND  |   49    |  25   |   17    |
----------------------------------------------------------------------------

Please note that I can only verify the DD-50P connector.  The Mini
Micro and DD-50SA pinout above is a pin for pin mapping from the SCSI
pinout in the FAQ.

How to tell if you have a single ended or differential drive:
    - Use an ohm meter to check the resistance between pins 21 & 22.
      On a single ended system, they should both be tied together
          and tied to GND.  On the differential drive, they should
          be open or have a significant resistance between them.  Note
          that most drives today are single ended so you usually only
          have to worry about this with old drives scavenged from
          other systems.




====
QUESTION: What are the pinouts for SCSI connectors?
ANSWER From: [e-mail] (Bob Snively)
====

Originally dated May 23, 1990

The connector families described by the drawings have standard
pin numberings which are described the same way by all vendors
that I have encountered.  The SCSI-2 specification identifies the
standard numbering, using that convention.  It happened to be
documented by AMP, but all the vendors use the same convention.

The following diagrams have the outline drawings of connector
sockets at the bottom.  This is really for reference only, because
the connector sockets and plugs are both specified as to their
numbering and usually are labeled.

There are some minor problems in naming the microconnector conductor
pairs, which I have corrected in the enclosed diagram.  All the conductor
pairs of the Mini-Micro (High Density) connector are in fact passed
through on the cables.  SCSI-2 defines the RSR (Reserved) lines as
maybe ground or maybe open, but they are still passed through the cable.
Most present standard SCSI devices will ground those lines.

--------------------  microSCSI to SCSI Diagram   ---------------------------


                       SCSI Connector Pinouts

_____________________________________  _____________________________________
| SCSI  |         | MINI  |         |  | SCSI  |        | MINI  |          |
| SIGNAL| DD-50P  | MICRO | DD-50SA |  | SIGNAL| DD-50P | MICRO | DD-50SA  |
------------------------------------  -------------------------------------
| -DB(0)|    2    |  26   |   34    |  |  GND  |    1    |   1   |    1    |
| -DB(1)|    4    |  27   |    2    |  |  GND  |    3    |   2   |   18    |
| -DB(2)|    6    |  28   |   19    |  |  GND  |    5    |   3   |   35    |
| -DB(3)|    8    |  29   |   36    |  |  GND  |    7    |   4   |    3    |
| -DB(4)|   10    |  30   |    4    |  |  GND  |    9    |   5   |   20    |
| -DB(5)|   12    |  31   |   21    |  |  GND  |   11    |   6   |   37    |
| -DB(6)|   14    |  32   |   38    |  |  GND  |   13    |   7   |    5    |
| -DB(7)|   16    |  33   |    6    |  |  GND  |   15    |   8   |   22    |
| -DB(P)|   18    |  34   |   23    |  |  GND  |   17    |   9   |   39    |
|  GND  |   20    |  35   |   40    |  |  GND  |   19    |  10   |    7    |
|  GND  |   22    |  36   |    8    |  |  GND  |   21    |  11   |   24    |
|  RSR  |   24    |  37   |   25    |  |  RSR  |   23    |  12   |   41    |
|TERMPWR|   26    |  38   |   42    |  |  OPEN |   25    |  13   |    9    |
|  RSR  |   28    |  39   |   10    |  |  RSR  |   27    |  14   |   26    |
|  GND  |   30    |  40   |   27    |  |  GND  |   29    |  15   |   43    |
| -ATN  |   32    |  41   |   44    |  |  GND  |   31    |  16   |   11    |
|  GND  |   34    |  42   |   12    |  |  GND  |   33    |  17   |   28    |
|  BSY  |   36    |  43   |   29    |  |  GND  |   35    |  18   |   45    |
| -ACK  |   38    |  44   |   46    |  |  GND  |   37    |  19   |   13    |
| -RST  |   40    |  45   |   14    |  |  GND  |   39    |  20   |   30    |
| -MSG  |   42    |  46   |   31    |  |  GND  |   41    |  21   |   47    |
| -SEL  |   44    |  47   |   48    |  |  GND  |   43    |  22   |   15    |
| -C/D  |   46    |  48   |   16    |  |  GND  |   45    |  23   |   32    |
| -REQ  |   48    |  49   |   33    |  |  GND  |   47    |  24   |   49    |
| -I/O  |   50    |  50   |   50    |  |  GND  |   49    |  25   |   17    |
----------------------------------------------------------------------------

 * NC = NOT CONNECTED

 CONNECTOR TYPES:
                                  DD-50SA
                        ________________________            MINI-MICRO
       DD-50P          |   -------------------  |      _____________________
    ______________     |17 \o o o o o o o o o/1 |     |  _________________ |
 49| o o o o o o |1    | 33 \ o o o o o o o /18 |     |25\ o o o o o o o /1|
 50| o o o o o o |2    |  50 \o o o o o o o/ 34 |     | 50\o o o o o o o/26|
   ---------------     |      -------------     |     |   --------------   |
                       --------------------------     ----------------------

(VIEWED FROM FACE OF CONNECTOR -  USE VENDOR NUMBERING SYSTEM AS SPECIFIED)


ANSWER From: Gary Field ([e-mail])

                    Macintosh Plus SCSI Connector Pinouts

Note that this connector is NON COMPLIANT WITH ANY SCSI STANDARD!
The grounding is insufficient and does not allow for proper twisted-pair
transmission line implementation. It is recommended that a short adapter cable
be used to convert to the more common Centronics style 50 pin connection
rather than extend the 25 pin connection any further than necessary.
The Macintosh Plus used a NCR 5380 SCSI chip controlled by the MC68000
processor.
___________________
| SCSI  |         |
| SIGNAL| DB-25S  |
+-----------------+        DB-25S (female)
| -DB(0)|    8    |           _____________________________
| -DB(1)|    21   |         13\ o o o o o o o o o o o o o /1
| -DB(2)|    22   |          25\ o o o o o o o o o o o o /14
| -DB(3)|    10   |             ------------------------
| -DB(4)|    23   |        View from rear of computer.
| -DB(5)|    11   |
| -DB(6)|    12   |
| -DB(7)|    13   |
| -DB(P)|    20   |
|  GND  | 7,9,14  |
|  GND  |16,18,24 |
| -ATN  |    17   |
|  BSY  |    6    |
| -ACK  |    5    |
| -RST  |    4    |
| -MSG  |    2    |
| -SEL  |    19   |
| -C/D  |    15   |
| -REQ  |    1    |
| -I/O  |    3    |
+-----------------+
Pin 25 is NOT CONNECTED



--
--/*   Gary A. Field - WA1GRC, Wang Labs M/S 019-72B, 1 Industrial Ave
   Lowell, MA 01851-5161,  [phone], email: [e-mail], EST5EDT
                   A waist is a terrible thing to mind!             */




Newsgroups: comp.periphs.scsi,comp.answers,news.answers
From: [e-mail] (Gary Field)
Subject: comp.periphs.scsi FAQ part 2 of 2
Expires: Sun, 1 May 1994 05:00:03 GMT
Reply-To: [e-mail] (Gary Field)
Organization: Wang Labs, Lowell MA, USA
Date: Mon, 4 Apr 1994 15:21:30 GMT
Approved: [e-mail]
Followup-To: comp.periphs.scsi
Summary: This posting contains a list of Frequently Asked
             Questions (and their answers) about SCSI.  It
             should be read by anyone who wishes to post to the
             comp.periphs.scsi newsgroup.
Sender: [e-mail]
Nntp-Posting-Host: gfield.wiis.wang.com
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Xref: bloom-beacon.mit.edu comp.periphs.scsi:13522 comp.answers:4769 news.answers:17656

Archive-name: scsi-faq/part2

                  SCSI FAQ:
       Frequently Asked Questions for comp.periphs.scsi

                  VOLUME II

Volume II Table of Contents:
    What is the difference between SCSI-1 and SCSI-2?
    Is SYNCHRONOUS faster than ASYNCHRONOUS?
    Is the 53C90 Faster than spec?
    What are the jumpers on my Conner drive?
    What are the jumpers for my Wangtek 5150 drive?
    What is CAM?
    What is FPT (Termination)?
    What is Active Termination?
    Why Is Active Termination Better?
    Why is SCSI more expensive than IDE?
    What is Plug and Play SCSI?
    Where can I get drivers (ASPI and other) for the WD7000 FASST2 host adapter?

====
QUESTION: What is the difference between SCSI-1 and SCSI-2?
ANSWER From Dal Allen:
====

                          SCSI-1_versus_SCSI-2

In 1985, when the first SCSI standard was being finalized as an American
National Standard, the X3T9.2 Task Group was approached by a group of
manufacturers.  The group wanted to increase the mandatory requirements of
SCSI and to define further features for direct-access devices.  Rather than
delay the SCSI standard, X3T9.2 formed an ad hoc group to develop a working
paper that was eventually called the Common Command Set (CCS).  Many products
were designed to this working paper.

In parallel with the development of the CCS working paper, X3T9.2 sought
permission to begin working on an enhanced SCSI standard, to be called SCSI-2.
SCSI-2 would include the results of the CCS working paper, caching commands,
performance enhancement features, and whatever else X3T9.2 deemed worthwhile.
While SCSI-2 was to go beyond the original SCSI standard (now referred to as
SCSI-1), it was to retain a high degree of compatibility with SCSI-1 devices.

How is SCSI-2 different from SCSI-1?

1.  Several options were removed from SCSI-1:

   a.  Single initiator option was removed.
   b.  Non-arbitrating Systems option was removed.
   c.  Non-extended sense data option was removed.
   d.  Reservation queuing option was removed.
   e.  The read-only device command set was replaced by the CD-ROM command
       set.
   f.  The alternative 1 shielded connector was dropped.


2.  There are several new low-level requirements in SCSI-2:

   a.  Parity must be implemented.
   b.  Initiators must provide TERMPWR -- Targets may provide TERMPWR.
   c.  The arbitration delay was extended to 2.4 us from 2.2 us.
   d.  Message support is now required.


3.  Many options significantly enhancing SCSI were added:

   a.  Wide SCSI (up to 32 bits wide using a second cable)
   b.  Fast SCSI (synchronous data transfers of up to 10 Mega-transfers per
       second -- up to 40 MegaBytes per second when combined with wide SCSI)
   c.  Command queuing (up to 256 commands per initiator on each logical unit)
   d.  High-density connector alternatives were added for both shielded and
       non- shielded connectors.
   e.  Improved termination for single-ended buses (Alternative 2)
   f.  Asynchronous event notification
   g.  Extended contingent allegiance
   h.  Terminate I/O Process messaging for time- critical process termination

4.  New command sets were added to SCSI-2 including:

   a.  CD-ROM (replaces read-only devices)
   b.  Scanner devices
   c.  Optical memory devices (provides for write-once, read-only, and
       erasable media)
   d.  Medium changer devices
   e.  Communications devices


5.  All command sets were enhanced:

   a.  Device Models were added
   b.  Extended sense was expanded to add:
       + Additional sense codes
       + Additional sense code qualifiers
       + Field replaceable unit code
       + Sense key specific bytes

   c.  INQUIRY DATA was expanded to add:
       + An implemented options byte
       + Vendor identification field
       + Product identification field
       + Product revision level field
       + Vital product data (more extensive product reporting)

   d.  The MODE SELECT and MODE SENSE commands were paged for all device types
   e.  The following commands were added for all device types:

       + CHANGE DEFINITION
       + LOG SELECT
       + LOG SENSE
       + READ BUFFER
       + WRITE BUFFER

   f.  The COPY command definition was expanded to include information on how
       to handle inexact block sizes and to include an image copy option.
   g.  The direct-access device command set was enhanced as follows:

       + The FORMAT UNIT command provides more control over defect management
       + Cache management was added:
          - LOCK/UNLOCK CACHE command
          - PREFETCH command
          - SYNCHRONIZE CACHE command
          - Force unit access bit
          - Disable page out bit

       + Several new commands were added:
          - READ DEFECT DATA
          - READ LONG
          - WRITE LONG
          - WRITE SAME

       + The sequential-access device command set was enhanced as follows:

          - Partitioned media concept was added:
            * LOCATE command
            * READ POSITION command

          - Several mode pages were added
          - Buffered mode 2 was added
          - An immediate bit was added to the WRITE FILEMARKS command

       + The printer device command set was enhanced as follows:
          - Several mode pages defined:
            * Disconnect/reconnect
            * Parallel printer
            * Serial printer
            * Printer options

       + The write-once (optical) device command set was enhanced by:
          - Several new commands were added:
            * MEDIUM SCAN
            * READ UPDATED BLOCK
            * UPDATE BLOCK

          - Twelve-byte command descriptor blocks were defined for several
            commands to accommodate larger transfer lengths.

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

The following article was written by Dal Allan of ENDL in April 1990.  It
was published nine months later in the January 1991 issue of "Computer
Technology Review".  While it appeared in the Tape Storage Technology
Section of CTR, the article is general in nature and tape-specific.  In
spite of the less than timely publication, most of the information is still
valid.

It is reprinted here with the permission of the author.  If you copy this
article, please include this notice giving "Computer Technology Review"
credit for first publication.

------------------------------------------------------------------------------
                            What's New in SCSI-2

Scuzzy is the pronunciation and SCSI (Small Computer System Interface) is
the acronym, for the best known and most widely used ANSI (American National
Standards Institute) interface.

Despite use of the term "Small" in its name, everyone has to agree that
Scuzzy is large - in use, in market impact, in influence, and unfortunately,
in documentation. The standards effort that began with a 20-page
specification in 1980 has grown to a 600 page extravaganza of technical
information.

Even before ANSI (American National Standards Institute) published the first
run of SCSI as standards document in 1986, ASC (Accredited Standards
Committee) X3T9.2 was hard at work on SCSI-2.

No technical rationale can be offered as to why SCSI-1 ended and SCSI-2
began, or as to why SCSI-2 ended and SCSI-3 began. The justification is much
more simple - you have to stop sometime and get a standard printed. Popular
interfaces never stop evolving, adapting, and expanding to meet more uses
than originally envisaged.

Interfaces even live far beyond their technological lifespan. SMD (Storage
Module Drive) has been called technically obsolete for 5 years but every
year there are more megabytes shipped on the SMD interface than the year
before. This will probably continue for another year or so before the high
point is reached, and it will at least a decade before SMD is considered to
be insignificant.

If SCSI enhancements are cut off at an arbitrary point, what initiates the
decision? Impatience is as good an answer as any. The committee and the
market get sick of promises that the revision process will "end soon," and
assert pressure to "do it now."

The SCSI-3 effort is actively under way right now, and the workload of the
committee seems to be no less than it was a year ago. What is pleasant, is
that the political pressures have eased.

There is a major difference between the standards for SCSI in 1986 and SCSI-
2 in 1990. The stated goal of compatibility between manufacturers had not
been achieved in SCSI in 1986 due to a proliferation of undocumented
"features."

Each implementation was different enough that new software drivers had to be
written for each device. OEMs defined variations in hardware that required
custom development programs and unique microcode. Out of this diversity
arose a cry for commonality that turned into CCS (Common Command Set), and
became so popular that it took on an identity of its own.

CCS defined the data structures of Mode Select and Mode Sense commands,
defect management on the Format command and error recovery procedures. CCS
succeeded because the goals were limited, the objectives clear and the time
was right.

CCS was the beginning of SCSI-2, but it was only for disks. Tape and optical
disks suffered from diversity, and so it was that the first working group
efforts on SCSI-2 were focused on tapes and optical disks. However, opening
up a new standards effort is like lifting the lid on Pandora's Box - it's
hard to stay focused on a single task. SCSI-2 went far beyond extending and
consolidating CCS for multiple device types.

SCSI-2 represents three years of creative thought by some of the best minds
in the business. Many of the new features will be useful only in advanced
systems; a few will find their way into the average user's system. Some may
never appear in any useful form and will atrophy, as did some original SCSI
features like Extended Identify.

Before beginning coverage of "what's new in SCSI-2," it might be well to
list some of the things that aren't new. The silicon chips designed for SCSI
are still usable. No new features were introduced which obsolete chips. The
cause of silicon obsolescence has been rapid market shifts in integrating
functions to provide higher performance.

Similarly, initiators which were designed properly, according to SCSI in
1986, will successfully support SCSI-2 peripherals. However, it should be
pointed out that not all the initiators sold over the last few years behaved
according to the standard, and they can be "blown away "by SCSI-2 targets.

The 1986 standard allows either initiators or targets to begin negotiation
for synchronous transfers, and requires that both initiators and targets
properly handle the sequence. A surprisingly large percentage of SCSI
initiators will fail if the target begins negotiation. This has not been as
much of a problem to date as it will become in the future, and you know as
well as I do, that these non-compliant initiators are going to blame the
SCSI-2 targets for being "incompatible."

Quirks in the 1986 standard, like 4 bytes being transferred on Request
Sense, even if the requested length was zero have been corrected in SCSI-2.
Initiators which relied on this quirk instead of requesting 4 bytes will get
into trouble with a SCSI-2 target.

A sincere effort has been made to ensure that a 1986-compliant initiator
does not fail or have problems with a SCSI-2 target. If problems occur, look
for a non-compliant initiator before you blame the SCSI-2 standard.

After that little lecture, let us turn to the features you will find in
SCSI-2 which include:

 o Wide SCSI: SCSI may now transfer data at bus widths of 16 and 32 bits.
Commands, status, messages and arbitration are still 8 bits, and the B-Cable
has 68 pins for data bits. Cabling was a confusing issue in the closing days
of SCSI-2, because the first project of SCSI-3 was the definition of a 16-
bit wide P-Cable which supported 16-bit arbitration as well as 16-bit data
transfers. Although SCSI-2 does not contain a definition of the P-Cable, it
is quite possible that within the year, the P-Cable will be most popular
non-SCSI-2 feature on SCSI-2 products. The market responds to what it wants,
not the the arbitrary cutoffs of standards committees.

 o Fast SCSI: A 10 MHz transfer rate for SCSI came out of a joint effort
with the IPI (Intelligent Peripheral Interface) committee in ASC X3T9.3.
Fast SCSI achieves 10 Megabytes/second on the A-Cable and with wider data
paths of 16- and 32-bits can rise to 20 Megabytes/second and even 40
Megabytes/second. However, by the time the market starts demanding 40
Megabytes/second it is likely that the effort to serialize the physical
interface for SCSI-3 will attract high-performance SCSI users to the Fiber
Channel.

A word of caution. At this time the fast parameters cannot be met by the
Single Ended electrical class, and is only suitable for Differential. One of
the goals in SCSI-3 is to identify the improvements needed to achieve 10 MHz
operation with Single Ended components.

 o Termination: The Single Ended electrical class depends on very tight
termination tolerances, but the passive 132 ohm termination defined in 1986
is mismatched with the cable impedance (typically below 100 ohms). Although
not a problem at low speeds when only a few devices are connected,
reflections can cause errors when transfer rates increase and/or more
devices are added. In SCSI-2, an active terminator has been defined which
lowers termination to 110 ohms and is a major boost to system integrity.

 o Bus Arbitration, Parity and the Identify Message were options of SCSI,
but are required in SCSI-2. All but the earliest and most primitive SCSI
implementations had these features anyway, so SCSI-2 only legitimizes the de
facto market choices. The Identify message has been enhanced to allow the
target to execute processes, so that commands can be issued to the target
and not just the LUNs.

 o Connectors: The tab and receptacle microconnectors chosen for SCSI-2 are
available from several sources. A smaller connector was seen as essential
for the shrinking form factor of disk drives and other peripherals. This
selection was one of the most argued over and contentious decisions made
during SCSI-2 development.

 o Rotational Position Locking: A rose by any other name, this feature
defines synchronized spindles, so than an initiator can manage disk targets
which have their spindles locked in a known relative position to each other.
Synchronized disks do not all have to be at Index, they can be set to an
offset in time relative to the master drive. By arraying banks of
synchronized disks, faster transfer rates can be achieved.

 o Contingent Allegiance: This existed in SCSI-1, even though it was not
defined, and is required to prevent the corruption of error sense data.
Targets in the Contingent Allegiance state reject all commands from other
initiators until the error status is cleared by the initiator that received
the Check Condition when the error occurred.

Deferred errors were a problem in the original SCSI but were not described.
A deferred error occurs in buffered systems when the target advises Good
Status when it accepts written data into a buffer. Some time later, if
anything goes wrong when the buffer contents are being written to the media,
you have a deferred error.

 o Extended Contingent Allegiance (ECA): This extends the utility of the
Contingent Allegiance state for an indefinite period during which the
initiator that received the error can perform advanced recovery algorithms.

 o Asynchronous Event Notification (AEN): This function compensates for a
deficiency in the original SCSI which did not permit a target to advise the
initiator of asynchronous events such as a cartridge being loaded into a
tape drive.

 o Mandatory Messages: The list of mandated messages has grown:

  +----------------------+--------------------------+-------------------+
  |       Both           |       Target             |     Initiator     |
  +----------------------+--------------------------+-------------------|
  | Identify             | Abort                    | Disconnect        |
  |                      |                          |                   |
  | Message Reject       | No Operation             | Restore Pointer   |
  |                      |                          |                   |
  | Message Parity Error | Bus Device Reset         | Save Data Pointer |
  |                      |                          |                   |
  |                      | Initiator Detected Error |                   |
  +----------------------+--------------------------+-------------------+

 o Optional messages have been added to negotiate wide transfers and Tags to
support command queueing. A last-minute inclusion in SCSI-2 was the ability
to Terminate I/O and receive the residue information in Check Condition
status (so that only the incomplete part of the command need be re-started
by the initiator).

 o Command Queueing: In SCSI-1, initiators were limited to one command per
LUN e.g. a disk drive. Now up to 256 commands can be outstanding to one LUN.
The target is allowed to re-sequence the order of command execution to
optimize seek motions. Queued commands require Tag messages which follow the
Identify.

 o Disk Cacheing: Two control bits are used in the CDB (Command Descriptor
Block) to control whether the cache is accessed on a Read or Write command,
and some commands have been added to control pre-fetching and locking of
data into the cache. Users do not have to change their software to take
advantage of cacheing, however, as the Mode Select/Mode Sense Cache page
allows parameters to be set which optimize the algorithms used in the target
to maximize cache performance. Here is another area in which improvements
have already been proposed in SCSI-3, and will turn up in SCSI-2 products
shipping later this year.

 o Sense Keys and Sense Codes have been formalized and extended. A subscript
byte to the Sense Code has been added to provide specifics on the type of
error being reported. Although of little value to error recovery, the
additional information about error causes is useful to the engineer who has
to analyze failures in the field, and can be used by host systems as input
to prognostic analysis to anticipate fault conditions.

 o Commands: Many old commands have been reworked and several new commands
have been added.

 o Pages: Some method had to be found to pass parameters between host and
target, and the technique used is known as pages. The concept was introduced
in CCS and has been expanded mightily in SCSI-2.

A number of new Common Commands have been added, and the opcode space for
10-byte CDBs has been doubled.

 o Change Definition allows a SCSI-2 initiator to instruct a SCSI-2 target
to stop executing according to the 1986 standard, and provide advanced SCSI-
2 features. Most SCSI-2 targets will power on and operate according to the
1986 standard (so that there is no risk of "disturbing" the installed
initiators, and will only begin operating in SCSI-2 mode, offering access to
the advanced SCSI-2 capabilities, after being instructed to do so by the
initiator using the Change Definition command.

 o The Mode Select and Mode Sense pages which describe parameters for
operation have been greatly expanded, from practically nothing in 1986 to
hundreds of items in SCSI-2. Whenever you hear of something being described
as powerful and flexible tool, think complicated. Integrators are advised to
be judicious in their selection of the pages they decide to support.

 o the Inquiry command now provides all sorts of interesting data about the
target and its LUNs. Some of this is fixed by the standard, but the main
benefit may be in the Vendor Unique data segregated into the special
designation of Vital Product Data, which can be used by integrators as a
tool to manage the system environment.

 o Select Log and Sense Log have been added so that the initiator can gather
both historical (e.g. all Check Conditions) and statistical (e.g. number of
soft errors requiring ECC) data from the target.

 o Diagnostic capabilities have been extended on the Read/Write Buffer and
Read/Write Long commands. The ways in which the target can manage bad blocks
in the user data space have been defined further and regulated to reduce
inconsistencies in the 1986 standard. A companion capability to Read Defect
Data permits the initiator to use a standard method to be advised of drive
defect lists.

 o A new group of 12-byte command blocks has been defined for all optical
devices to support the large volume sizes and potentially large transfer
lengths. The Erase command has been added for rewritable optical disks so
that areas on the media can be pre-erased for subsequent recording. Write
Once disks need Media Scan, so that the user can find blank areas on the
media.

 o New command sets have been added for Scanners, Medium Changers, and CD
ROMs.

All of this technical detail can get boring, so how about some "goodies" in
SCSI-2 which benefit the common man and help the struggling engineer? First,
and probably the best feature in SCSI-2 is that the document has been
alphabetized. No longer do you have to embark on a hunt for the Read command
because you cannot remember the opcode.

In the 1986 standard, everything was in numeric sequence, and the only
engineers who could find things easily were the microprogrammers who had
memorized all the message and opcode tables. Now, ordinary people can find
the Read command because it is in alphabetic sequence. This reorganization
may sound like a small matter but it wasn't, it required a considerable
amount of effort on the part of the SCSI-2 editors. It was well worth it.

Another boon is the introduction for each device class of models which
describe the device class characteristics. The tape model was the most
needed, because various tape devices use the same acronym but with different
meanings or different acronyms for the same meaning.

The SCSI-2 tape model defines the terms used by SCSI-2, and how they
correspond to the acronyms of the different tapes. For example, on a 9-track
reel, End of Tape is a warning, and there is sufficient media beyond the
reflective spot to record more data and a trailer. Not so on a 1/4" tape
cartridge, End of Tape means out of media and no more data can be written.
This sort of difference in terms causes nightmares for standardization
efforts.

So there it is, a summary of what is in SCSI-2. It's not scary, although it
is daunting to imagine plowing through a 600-page document. Time for a
commercial here. The "SCSI Bench Reference" available from ENDL Publications
(408-867-6642), is a compaction of the standard. It takes the 10% of SCSI-2
which is constantly referenced by any implementor, and puts it in an easy-
to-use reference format in a small handbook. The author is Jeff Stai, one of
the earliest engineers to become involved with SCSI implementation, and a
significant contributor to the development of both the 1986 standard and
SCSI-2.

SCSI-2 is not yet published as a standard, but it will be available later
this year. Until then, the latest revision can be purchased from Global
Engineering (800-854-7179).

Biography

Consultant and analyst I. Dal Allan is the founder of ENDL and publisher of
the ENDL Letter and the "SCSI Bench Reference." A pioneer and activist in
the development and use of standard interfaces, he is Vice Chairman of ASC
X3T9.2 (SCSI) and Chairman of the SCSI-2 Common Access Method Committee.





====
QUESTION: Is SYNCHRONOUS faster than ASYNCHRONOUS?
QUESTION: Is the 53C90 Faster than spec?
From: [e-mail] (Ken Stewart)
====

I've seen a few comments about our 54C90 being faster than spec.  While
I doubt the author was really complaining (I got twice as much as I paid
for--sure makes me mad ;)  I'd like to explain the situation.

Along the way, I'll also show that asynchronous is faster on short cables,
while synchronous is faster on long cables.  The cross-over point occurs
somewhere around six feet--assuming that you have our 53C90 family devices
at both ends of the cable.  The reason has to do with the propagation delay
of the cable; the turn around time of the silicon; and the interlocked nature
of the asynchronous handshake.

1)  We have measured propagation delays from various cables and found an
    average of 1.7 nanoseconds per foot, which is roughly 5.25 ns per meter.

2)  The turn-around time is the amount of time the SCSI chip takes to
    change an output in response to an input.  If REQ is an input then ACK
    is an output.  Or if ACK is an input then REQ is an output.  Typical
    turn-around time for the 53C90 is 40 nanoseconds.

3)  The asynchronous transfer uses an interlocked handshake where a device
    cannot do the next thing until it receives positive acknowledgment that
    the other device received the last thing.

    First REQ goes true                        /* driven by Target */
    then ACK is permitted to go true           /* driven by Initiator */
    then REQ is permitted to go false
    then ACK is permitted to go false

Thus we have four "edges" propagating down the cable plus 4 turn-around
delays.  Asynchronous transfer requires 55 ns setup and no hold time
(paragraph in 5.1.5.1 in SCSI-1 or SCSI-2) which gives an upper speed
limit around 18 MB/s.  A detailed analysis (assuming 53C90 family) shows that
the setup time subtracts out.  This is mostly because we are running at
one-third the max rate, but also because setup for the next byte can begin
anytime after ACK is received true or REQ is received false, depending on who
is receiving.  You can either take my word for it or draw the waveforms
yourself.  Thus, the asynchronous transfer reduces to:

(4 * 1.7 * 1) + (4 * 40ns) = 167 ns                /* 1 foot cable */
                           = 6 MB/s

(4 * 5.25 * 6) + (4 * 40ns) = 286 ns               /* 6 meter cable */
                            = 3.5 MB/s

(4 * 5.25 * 25) + (4 * 40ns) = 685 ns              /* 25 meter cable */
                             = 1.5 MB/s

note: cables longer than 6 meters require external differential transceivers
which add delay and degrade the performance even more than indicated here.

Our simulations say that under very best conditions (fast silicon, low
temperature, high voltage, zero length cable) we can expect more than 8 MB/s
asynchronously.  In the lab, I routinely measure 5 MB/s on 8 foot cables.
So, if you were writing the data manual for this, how would YOU spec it?


The framers of the SCSI spec threw in synchronous mode to boost the
performance on long cables.  In synchronous mode, the sending device is
permitted to send the next byte without receiving acknowledgment that the
receiver actually received the last byte.  Kind of a ship and pray method.
The acknowledgment is required to come back sometime, but we just don't have
to wait for it (handwave the offset stuff and the ending boundary
conditions).  In this mode any external transceivers add a time shift, but
not a delay.  So if you negotiate for 5 MB/s, you get 5MB/s regardless how
long the cable is and regardless whether you are single-ended or
differential.  But you can't go faster than 5.5 MB/s, except in SCSI-2.
Synchronous mode does have a hold time (unlike asynch) but again, setup and
hold times subtract out.  In SCSI-1 synchronous mode, the speed limit comes
from the combined ASSERTION PERIOD + NEGATION PERIOD which is
90ns + 90ns = 180ns = 5.5 MB/s.  Our 53C90 family doesn't quite hit the max,
but we do guarentee 5.0 MB/s.  In SCSI-2, anything above 5.0 MB/s is
considered to be FAST.  Here the maximum transfer rate is explicitly limited
to 100 ns or 10MB/s; you don't have to read between the lines to deduce it.

Interesting tid-bit: given a SCSI-2 FAST period of 100 ns and a cable delay
of 131 ns on a 25 meter cable, you can actually stack 1.31 bytes in the 8-bit
cable.  In FAST and WIDE SCSI you can stack 5.24 bytes in this copper FIFO.
Hummm...



====
QUESTION: What are the jumpers on my Conner drive?
ANSWER From: [e-mail] (Eric Krieger)
Embellishment from: Henrik Stahl ([e-mail])
====

               QUICK INSTALLATION GUIDE

                         SCSI

     Most SCSI host adapters are compatible with Conner drives.
Software drivers and installation instructions are provided with
the host adapter.

     The drives are shipped with SCSI ID set to 7. To select a
different ID refer to the following:

Table A                       Table B
ID   E-1  E-2  E-3            ID   E2   E3   E4
0    out  out  out            0    out  out  out
1    in   out  out            1    in   out  out
2    out  in   out            2    out  in   out
3    in   in   out            3    in   in   out
4    out  out  in             4    out  out  in
5    in   out  in             5    in   out  in
6    out  in   in             6    out  in   in
7    in   in   in             7    in   in   in

Parity is always ENABLED on the CP3200,CP30060,CP30080,CP30100,
CP 30200, CP 3500, CP 3360, CP 30540 and CP 31370.

For the CP 340, jumper E-1 to disable parity.

All other models, jumper E-4 to disable parity.

     SCSI drive parameters:

     Model          Hds       Cyl       Sec       Table     LED
     CP2020         2         642       32        A         n/a
     CP340          4         788       26        B         1
     CP3020         2         622       33        A         1
     CP3040         2        1026       40        A         1
     CP3180         6         832       33        A         1
     CP3100         8         776       33        A         1
     CP30060        2        1524       39        A         2
     CP30080        4        1053       39        A         2
     CP30100        4        1522       39        A         2
     CP30200        4        2119       49        A         2
     CP3200         8        1366       38        A         2
     CP3360         8        1806       49        A         2
     CP3540         12       1806       49        A         2
     CP 30080E      2        1806      46         AA       C/E
     CP 30170E      4        1806      46         AA       C/E
     CP 30540       6        2249      59-89      AA        B
     CP 31370       14       2094      59-95      AA        B

LED 1               LED 2
J-4  Pin 1 = +      J-1 Pin 3 = +
     Pin 2 = -          Pin 4 = -

On the CP 31370, jumper E5 enables termination. Default is termination on.
It may be the same jumper for other models.



====
QUESTION: What are the jumpers for my Wangtek 5150 drive?
ANSWER From: "Terry Kennedy, Operations Mgr" <uunet!spcvxa.spc.edu!TERRY>
====

  First, the disclaimer: This is not an official representation of Wangtek
or of my employer. This is info I've discovered by reading publicly avail-
able reference material. When changing jumpers, always observe proper anti-
static precautions and be sure you have the current configuration written
down so you have a known starting point.

  Ok. Here's the complete scoop on Wangtek 5150ES drives:

  The current part number for a "generic" 5150ES is:

  33685-201 (black faceplate)
  33685-202 (beige faceplate)

  These are referred to as the "ACA version" of the drive.

  There are _many_ other part numbers for 5150ES drives. If you have one that
isn't one of the above, it doesn't mean you have an old or an out of rev drive,
it just means it's a special version created for a distributor or OEM, or with
different default jumper settings.

  You can order the Wangtek 5150ES OEM Manual from Wangtek. It is part number
63045-001 Revision D.

  There are 5 possible logic boards. Here are the jumper options for each:

  Logic assembly #33678
  ---------------------

  (J10)
  0 - SCSI unit LSB
  1 - SCSI unit
  2 - SCSI unit MSB
  K - not documented

  J32 - Diagnostic test connector, default is not installed
  E1, F1 - SCSI termination power. E1 in = power from drive and to cable,
       E1 out - power from cable. F1 = terminator power fuse, 1.5A FB.
       Default is IN.
  E2 - Chassis ground. E2 in jumpers logic to chassis ground. E2 out isolates
       through a .33 uFD capacitor. Default is IN.
  E5 - Master oscillator enable. Test only. Must be IN.
  E20 - Factory test. Must be OUT.
  RP1, RP2, RP3 - SIP terminators. Default is IN, remove for no termination.

  Logic assembly #30559
  ---------------------

  HDR1 - Factory testing. Setting depends on drive. Don't touch.
  HDR2 - Factory testing. Defaults are pins 15-16, 17-18, 19-20. Don't touch.
  HDR3 pin 1 - A-B enables buffered mode. B-C disables. Can be overridden by
               SCSI Mode Select.
  HDR3 pin 2, 3 - Default data format. Set to B-C for a 5150ES.
  HDR3 pin 4 - parity enable. A-B enables, B-C disables.

  (J10)
  0 - SCSI unit LSB
  1 - SCSI unit
  2 - SCSI unit MSB
  K - not documented

  E1 - SCSI termination power. E1 in = power from drive and to cable,
       E1 out - power from cable.
  E2 - Chassis ground. E2 in jumpers logic to chassis ground. E2 out isolates
       through a .33 uFD capacitor. Default is IN.
  E3 - Master oscillator enable. Test only. Must be IN.
  E4 - Write test mode. Test only. Must be OUT.
  E5 - Write oscillator enable. Test only. Must be IN.
  E6 - Disable HDR2. Test only. Must be IN.
  E7 - Microcontroller clock select. In for a 5150ES.
  E8 - Write precomp select. Set on a per-drive basis. Don't touch.
  E9 - RAM size. Don't touch.
  E10 - Erase frequency. Don't touch.
  RP2, RP3 - DIP and SIP terminators. Default is IN, remove for no termination.

  Logic assembly #30600
  ---------------------

  HDR1 - Factory testing. Setting depends on drive. Don't touch.
  HDR2 - Write precomp select. Set on a per-drive basis. Don't touch.
  HDR3 pin 1, 2, 3 - SCSI device address. 1 is LSB, 3 is MSB. A-B=1, B-C=0
  HDR3 pin 4 - Parity enable. IA-B is enabled.
  HDR3 pin 5, 6 - Default data format. B-C for a 5150ES.
  HDR3 pin 7 - Buffered mode select. A-B is enabled.
  HDR3 pin 8 - Reserved. Must be OUT.
  HDR4 - Write frequency select. Don't touch.
  E1 - SCSI termination power. E1 in = power from drive and to cable,
       E1 out - power from cable.
  E2 - Chassis ground. E2 in jumpers logic to chassis ground. E2 out isolates
       through a .33 uFD capacitor. Default is IN.
  E3 - Hard/soft reset. IN enables hard reset.
  E4 - Write precomp select. Don't touch.
  E5 - Clock speed. Don't touch.
  E6 - Tape hole test. Don't touch.

  Logic assembly #30552
  ---------------------

  HDR1 - Factory testing. Setting depends on drive. Don't touch.
  HDR2 - Write precomp select. Set on a per-drive basis. Don't touch.
  HDR3 pin 1, 2, 3 - SCSI device address. 1 is LSB, 3 is MSB. [Note - HDR3
             pins 1-3 are duplicated at another location on the board]
  HDR3 pin 4 - Parity enable. IN is enabled.
  HDR3 pin 5, 6, 7, 8 - Default data format. 5,5 B-C, 7-8 A-B for a 5150ES.
  HDR4 - Write frequency select. Don't touch.
  E1 - SCSI termination power. E1 in = power from drive and to cable,
       E1 out - power from cable.
  E2 - Chassis ground. E2 in jumpers logic to chassis ground. E2 out isolates
       through a .33 uFD capacitor. Default is IN.
  E3 - Hard/soft reset. IN enables hard reset.
  E4 - Write precomp select. Don't touch.
  E5 - Clock speed. Don't touch.
  E6 - Tape hole test. Don't touch.

  Logic assembly #30427
  ---------------------

  HDR1 - Factory testing. Setting depends on drive. Don't touch.
  HDR2 - Write precomp select. Set on a per-drive basis. Don't touch.
  HDR3 pin 1, 2, 3 - SCSI device address. 1 is LSB, 3 is MSB. A-B=1, B-C=0
  HDR3 pin 4 - Parity enable. IA-B is enabled.
  HDR3 pin 5, 6, 7, 8 - Default data format. 5,5 B-C, 7-8 A-B for a 5150ES.
  E1, E3 - Factory test. Must be IN.
  E2 - SCSI termination power. E2 in = power from drive and to cable,
       E2 out - power from cable.
  E4 - Chassis ground. E4 in jumpers logic to chassis ground. E4 out isolates
       through a .33 uFD capacitor. Default is IN.

  Firmware - There are many flavors of firmware. I have seen the following
parts:

  24115-xxx
  24144-xxx
  21158-xxx

  the -xxx suffix changes as the firmware is updated. According to the folks
I spoke to at Wangtek, the standard firmware is the 21158. The latest version
as of this writing is 21158-007. All of these will work with the Adaptec and
GTAK.

  The firmware options (as returned by a SCSI Identify) are on the end of the
product string, which is "WANGTEK 5150ES SCSI ES41C560 AFD QFA STD" for the
21158-007 firmware. The 3-letter codes have the following meaning:

  AFD - Automatic Format Detection - the drive will recognize the format (such
    as QIC-24, QIC-120, or QIC-150) that the tape was written in.

  QFA - Quick File Access - the ability to rapidly locate a tape block, and
    to implement the "position to block" and "report block" SCSI commands.
    This is compatible with the Tandberg implementation.

  STD - Standard feature set.



====
QUESTION: What is CAM?
ANSWER From: [e-mail] (Clifton Jones)
====

Common Access Method.

It is a proposed ANSI standard to make it easier to program SCSI applications
by encapsulating the SCSI functions into a standardized calling convention.

ANSWER From: [e-mail] (Hale Landis)
====

You may be able to get the CAM spec(s) from the SCSI BBS




====
QUESTION: What is FPT (Termination)?
ANSWER From: [e-mail] (John Vincent)
====


FPT is actually really simple, I wish I had thought of it. What it does
is use diode clamps to eliminate over and undershoot. The "trick" is
that instead of clamping to +5 and GND they clamp to the output of two
regulated voltages. This allows the clamping diodes to turn on earlier
and is therefore better at eliminating overshoot and undershoot. The block
diagram for a FPTed signal is below. The resistor value is probably in the
120 to 130 ohm range. The actual output voltages of the regulators may not
be exaclty as I have shown them but ideally they are matched to the diode
characteristics so that conduction occurs when the signal voltage is
greater than 3.0 V or less than 0.5 V.



          +--------------- TERMPWR
          |
      ____|____
     |        |
     | Vreg 1 |-------*-------------------------*--------------- 3.? V
     |________|       |                         |
                      |                         |
                      |                         |
                      |                         \
         +------------*                         /    pullup resistor
         |            |                         \
         |            |                         /
         |        ____|___                      |
         |       |        |                     |
         |       | Vreg 2 |----------*----------|--------------- 3.0 V
         |       |________|          |          |
         |                         --+--        |
         |                          / \         |
         +-----------+             /___\        |
                     |               |          |
                     |               |          |              terminated
                     |               *----------*------------- signal
                     |               |
                     |               |
                     |             --+--
                     |              / \
                     |             /___\
                     |               |
                  ___|____           |
                 |        |          |
                 | Vreg 3 |----------*-------------------------  1.0 V (?)
                 |________|





====
QUESTION: What is Active Termination?
ANSWER From: [e-mail] (Eric Smith)
        and  [e-mail] (Brent R. Largent)
====


An active terminator actually has one or more voltage regulators to produce
the termination voltage, rather than using resistor voltage dividers.

This is a passive terminator:


TERMPWR     ------/\/\/\/------+------/\/\/\/-----  GND
                               |
                               |
                              SCSI signal

Notice that the termination voltage is varies with the voltage on the
TERMPWR line.  One voltage divider (two resistors) is used for each SCSI
signal.


An active terminator looks more like this (supply filter caps omitted):

               +-----------+
TERMPWR   -----| in    out |------+------/\/\/\/-------SCSI signal
               |   gnd     |      |
               +-----------+      |
                    |             +------/\/\/\/-------SCSI signal
                    |             |
GND  ---------------+             |
                                  +------/\/\/\/-------SCSI signal
                                  |
                                 etc.

Assuming that the TERMPWR voltage doesn't drop below the desired termination
voltage (plus the regulator's minimum drop), the SCSI signals will always
be terminated to the correct voltage level.

Several vendors have started making SCSI active terminator chips,
which contain the regulator and the resistors including Dallas
Semiconductor, Unitrode Integrated Circuits and Motorola




====
QUESTION: Why Is Active Termination Better?
ANSWER [e-mail] (Brent R. Largent)
====


Typical pasive terminators (resistors) fluctuate directly in relation to the
TERM Power Voltage. Usually terminating resistors will suffice over short distances,
like 2-3 feet, but for longer distances active termination is a real advantage. It
reduces noise.

 Active Termination provide numerous advantages:
- A logic bit can disconnect the termination
- Provides Negative Clamping on all signal lines
- Regulated termination voltage
- SCSI-2 spec recommends active termination on both ends of the scsi cable.
- Improved Resistance tolerences (from 1% to about 3%)




====
QUESTION: Why is SCSI more expensive than IDE?
ANSWER From: [e-mail] (Hale Landis)
====

In a typical single drive PC system, ATA (you call it IDE, the
proper name is ATA) is faster than any SCSI.  This is because of
the 1 to 2 millisecond command overhead of a SCSI host adapter
vs. the 100 to 300 microsecond command overhead of an ATA drive.
Also, ATA transfers data 16-bits at a time from the drive
directly to/from the system bus.  Compare this to SCSI which
transfers data 8-bits at a time between the host adapter and the
drive.  The host adapter may be able to transfer data 16-bits at
a time to the system bus.

Of course you could go to Fast SCSI or Wide SCSI but that costs
a whole bunch more!

But then you asked about cost.

The real reason SCSI costs more has to do with production volume.
There are about 120,000 drives made per day on this planet. 85%
of those drives are ATA.  The remainder are SCSI, IPI, SMD and a
few other strange interfaces.  The actual percent that are SCSI
is falling at a very very slow rate.  Without the production
volume, componet prices are higher, therefor drive prices are
higher.

And then you must add in the host adapter cost.  Compare $15 for
ATA vs.  $50 for a simple SCSI host adapter.  But you probably
want a higher quality SCSI host adapter so plan on spending $100
to $500 for one.

You figure out how to get people to buy more SCSI drives, say
50,000 per day, and maybe the prices will come down to ATA price
levels.  Plus you could probably get a very good marketing job at
any of the disk drive companies!  Of course, each day more and
more people are discovering the performance advantage of ATA so
your job may not be as easy as you would like.


====
QUESTION: What is Plug and Play SCSI?
ANSWER: [e-mail] (Lee Fisher) (Updated Dec 7 1993)
====

Plug and Play is the name of a technology that lets PC hardware and
attached devices work together automatically. A user can simply attach a
new device ("plug it in") and begin working ("begin playing"). This should
be possible even while the computer is running, without restarting it.
Plug and Play technology is implemented in hardware, in operating systems
such as Microsoft Windows, and in supporting software such as drivers and
BIOS.

With Plug and Play technology, users can easily add new capabilities to
their PCs, such as sound or fax, without having to concern themselves with
technical details or encountering problems. For users of mobile PCs (who
are frequently changing their configurations with docking stations,
intermittent network connections, etc.) Plug and Play technology will
easily manage their changing hardware configuration.  For all users, Plug
and Play will reduce the time wasted on technical problems and increase
their productivity and satisfaction with PCs.

The Plug and Play technology is defined in a series of specifications
covering the major component pieces. There are specifications for BIOS,
ISA cards, PCI, SCSI, IDE CD-ROM, PCMCIA, drivers, and Microchannel. In a
nutshell, each hardware device must be able to be uniquely identified, it
must state the services it provides and the resources which it requires,
it must identify the driver which supports it, and finally it must allow
software to configure it.

The first Plug and Play compliant products are available now, as are
development kits for drivers and hardware. Twenty different Plug and Play
products were shown at Comdex in November 1993.

Specifications:

The Plug and Play specifications are now available via anonymous ftp at
ftp.microsoft.com in the \drg\plug-and-play subdirectory. The files are
compressed in .zip format, and are in Microsoft Word format.)

  Plug and Play ISA files (.\pnpisa\*)

    errata.zip   Clarifications and corrections to pnpisa.doc
    isolat.zip   MS-DOS testing tool to isloate ISA PnP hardware
    pnpdos.zip   Plug and Play device driver interface specification
    pnpisa.zip   Hardware spec for PnP ISA enhancement
    vhdlzi.zip   Hardware spec for PnP ISA enhancement

  Plug and Play SCSI files (.\scsi_ide\*):

    pnpscsi.zip  Plug and Play SCSI specification proposal
    scam.zip     SCAM (SCSI Comnfigured Auto-Magically) specification

  Plug and Play BIOS files (.\bios\*):

    apmv11.zip   Advanced Power management spec v.1
    vios.zip     Plug and Play BIOS spec
    escd1.zip    Spec for optional method of storing config info for PnP BIOS

[e-mail] alias:

There is an alias, [e-mail], which you can email and get on
a Microsoft mailing list related to Plug and Play, where the Hardware
Vendor Relations Group (HVRG) will mail out new specifications,
announcements, information on workshops, Windows Hardwware Engineering
Conference (WinHEC), etc...

Compuserve PlugPlay forum:

There is a forum on Compuserve, GO PLUGPLAY. This forum is the method for
support, discussions and dialogs about Plug and Play. In addition, the
forum's library contains all of the current specification.

Intel Plug and Play kits:

If you are interested in Intel's two Plug and Play kits, either "Plug and
Play Kit for MS-DOS and Windows" or "Plug and Play BIOS Enhancements Kit",
FAX your name and company information to Intel at 1.503.696.1307, and
Intel will send you the information.


====
QUESTION: Where can I get drivers (ASPI and other) for the WD7000 FASST2
      host adapter?
ANSWER From: Gary Field ([e-mail])
====

    Western Digital stopped producing WD7000 FASST2 cards some time in
1990. Future Domain bought the rights to produce them and as of early 1994
they still do. Columbia Data Products Inc. of Altamonte Springs, Florida still
provides driver support for the card.
Their SST IV driver package provides support for many types of SCSI devices
including disks, tapes, and CDROM. Also included in this package is an ASPI
manager driver (equivalent to the Adaptec ASPI4DOS.SYS). I have personally
tested this ASPI manager and it works with GNU tar w/ASPI and the Corel CDROM
driver, so most other ASPI stuff should work too. Versions of SSTASPI.SYS
prior to Oct 1993 do NOT work with the above mentioned programs so be sure
to check the file date. There are other useful programs in the package as well.
For instance I find the TAPEUTIL program very handy for duplicating tapes.
The price of this package is $99 or $85 as an upgrade of a previous version.
A pre-requisite to run this software is that the adapter card must have a
BIOS ROM version of 3.36 or newer. I don't think cards manufactured before
1989 or so are compatible.

Columbia Data Products Inc.
1070 B Rainer Dr
Altamonte Springs, FL 32714 [phone]


====
End.
====



--
--/*   Gary A. Field - WA1GRC, Wang Labs M/S 019-72B, 1 Industrial Ave
   Lowell, MA 01851-5161,  [phone], email: [e-mail], EST5EDT
                   A waist is a terrible thing to mind!             */