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From: garyf@wiis.wang.com (Gary Field)
Subject: comp.periphs.scsi FAQ part 1 of 2
Expires: Fri, 1 Jul 1994 05:00:03 GMT
Reply-To: garyf@wiis.wang.com (Gary Field)
Organization: Wang Labs, Lowell MA, USA
Date: Thu, 2 Jun 1994 13:24:50 GMT
Approved: news-answers-request@MIT.Edu
Message-ID: <CqruLG.Mw5@wang.com>
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: news@wang.com
Nntp-Posting-Host: gfield.wiis.wang.com
Lines: 940
Xref: mmddvan comp.periphs.scsi:23542 comp.answers:5632 news.answers:23175
Archive-name: scsi-faq/part1
SCSI FAQ:
Frequently Asked Questions for comp.periphs.scsi
FAQ history: Created by Johnathan Vail (vail@tegra.com) from articles
submitted to him by comp.periph.scsi readers.
Maintained by Johnathan Vail until November 1993.
Current Editor: Gary Field (garyf@wiis.wang.com)
Last Modified: May 27, 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 telephone number of Fujitsu?
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?
What if I have a drive larger than a gigabyte (1024k) ?
====
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: burke@seachg.uucp (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: fishman@panix.com (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 (terry@spcvxa.spc.edu)
====
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
c