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From: garyf@wiis.wang.com (Gary Field)
Subject: comp.periphs.scsi FAQ part 2 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 13:27:35 GMT
Approved: news-answers-request@MIT.Edu
Message-ID: <Cqrupz.MzG@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: 1127
Xref: mmddvan comp.periphs.scsi:23543 comp.answers:5633 news.answers:23176
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?
What if I have a drive larger than a gigabyte (1024k) ?
====
QUESTION: What is the difference between SCSI-1 and SCSI-2?
ANSWER From Dal Allen:
====
SCSI-1{CBM-*}versus{CBM-*}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
interfa