SCSI FAQ - Part 2

Newsgroups: comp.periphs.scsi,comp.answers,news.answers
Subject: comp.periphs.scsi FAQ part 2 of 2
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Date: 02 Jun 1997 13:09:24 GMT
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Reply-To: (Gary Field)
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.
Xref: comp.periphs.scsi:87343 comp.answers:26319 news.answers:103964

Archive-name: scsi-faq/part2
Posting-Frequency: monthly
Last-modified: 1997/05/27

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

			      VOLUME 2

Volume 2 Table of Contents:
    What is the difference between SCSI-1 and SCSI-2?
    Is the 53C90 Faster than spec?
    What are the jumpers on my Conner drive?
    What are the jumpers for my Wangtek 5150 drive?
    How do I configure my HP DDS DAT tape drive?
    What is CAM?
    What is FPT (Termination)?
    What is Active Termination?
    Why Is Active Termination Better?
    How can I tell whether an unmarked terminator is active or passive?
    Where can I buy terminators ?
    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 (1024MB) ?
    My SCSI bus works, but is not reliable. What should I look at?
    Where can I find information about programming using the ASPI
          interface from DOS and Windows?
    How do I replace the Macintosh internal hard disk and terminate the
	SCSI bus properly?
    Will attaching a SCSI-1 device to my SCSI-2 bus hurt its performance?
    Can I connect a SCSI-3 disk to my SCSI-1 host adapter?
    Can I connect a SCSI-2 CDROM to my SCSI-3 host adapter?
    Can I connect a WIDE device to my narrow SCSI host adapter?
    Can I connect a narrow device to my WIDE SCSI host adapter?
    How does device ID numbering work with WIDE vs NARROW devices?

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


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
   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.  Your Great New Jersey Web Sited 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:

       + LOG SELECT
       + LOG SENSE
       + READ 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 

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 

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 

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 

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 

 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 

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

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 

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 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).


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: What is the difference between SCSI-2 and SCSI-3?
ANSWER From: excerpts of postings by Jeff Stai and others:
	(Mohit K Goyall -,
	(Andrew E. Lowman -

Are SCSI-3 hard drives and/or controllers available yet?

Allegedly.  Previous postings have said "I heard that SCSI-3 has been
standardized," but I haven't seen anything firm about it.  I've seen
controllers advertised by JDR Microdevices and some cheap clones; the
Quantum "Empire" drives are also advertised as SCSI-3 by some mail order
vendors.  Seagate and IBM call their fastest drives (probably comparable
in speed to the Quantums, if not faster) "Wide SCSI-2."

That's a misnomer. See below.

What is the difference between SCSI-3 and Fast & Wide SCSI-2?

Wide SCSI-2 required two cables to do 16 bit wide transfers. SCSI-3
defined a single cable, single REQ/ACK 16 bit wide transfer. The reason
you are hearing 16-bit single cable being called SCSI-3 is that they
CAN. The fact that single cable 16-bit has been around for a while just
shows you how much the standardization process lags behind the real

SCSI-3 is really a family of standards. SCSI was broken up from a
single document into different layers and command sets. This was done
to allow for different physical transport layers (like fibre channel
and SSA) to be defined, and to allow for smaller "bite-sized" projects
that maybe get done a little faster ;-)

The family includes the following members with TLAs:

- SCSI-3 Parallel Interface (SPI): Defines the mechanical, timing,
phases, and electrical parameters of the parallel cable we all know and
love. Some of the electrical and cable parameters are
tightened/improved over SCSI-2.

- SCSI-3 Interlock Protocol (SIP): Defines the messages and how the
phases are invoked. No real change from SCSI-2, except for some new

- SCSI-3 Architectural Model (SAM): In a nutshell, defines a common set
of functions and services and definitions for how a physical transport
properly gets commands, data, and status exchanged between two devices,
complete with error handling and queueing.

- SCSI-3 Primary Commands (SPC): All of the commands executed by any
and all SCSI devices, like REQUEST SENSE and INQUIRY, etc.

- SCSI-3 Block Commands (SBC): Disk commands.

- SCSI-3 Stream Commands (SBC): Tape commands.

- SCSI-3 Controller Commands (SCC): RAID box commands.

- SCSI-3 Multimedia Commands (MMC): For CDROMS etc.

- SCSI-3 Fibre Channel Protocol (FCP): SCSI commands over gigabit Fibre

- SCSI-3 Serial Bus Protocol (SBP): SCSI commands over IEEE 1394 High
Speed Serial Bus (Apple's "Firewire").

- SCSI-3 Serial Storage Protocol (SSP): SCSI commands over SSA.


After perusing the latest issue of Computer Shopper, I came
away with the impression that companies are calling
F&W scsi-2 hd's SCSI-3.  Is this an incorrect assumption,
or is F&W SCSI-2 known as SCSI-3?
Is this really mostly marketing hype?

Actually, there is something to that. TECHNICALLY, what is out there is
often a hybrid: SCSI-3 "SPI" silicon with some other hodgepodge of
SCSI-3 proposals, all mixed in with SCSI-2 stuff.

An earlier posting said that the Quantum Empire ("SCSI-3") drives
contain some commands from the SCSI-3 command set, and Adaptec 
suggested a specific setting on its 2940W controller to work properly
with the drive.

I understand there are some drives with proposed SCSI-3 command
features. These are mostly in the MODE SELECT and in error codes, as I
recall. Perhaps someone who knows more about this could elaborate?

Note also that the major players (like DC Drives) don't have any "SCSI-3"
stuff advertised; only JDR and some cheap clones are promoting it.
Besides, Wide SCSI-2 has yet to really catch on (mostly because only a
few drives are fast enough to take advantage of it).

There is no "wide SCSI-2" because that would mean two cables. Single
cable wide SCSI has always been SCSI-3, it just took too d*** long to
get into a standard!-)

QUESTION: Is the 53C90 Faster than spec?
ANSWER From: kstewart@ncr-mpd.FtCollins.NCR.COM (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 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.  

QUESTION: What are the jumpers on my Conner drive?
ANSWER From: (Eric Krieger)
Embellishment from: Henrik Stahl (



     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 (

  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

  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.

  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


  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

  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: How do I configure my HP DDS DAT tape drive?
ANSWER From: Alan Strassberg (

	The HP DDS Configuration Guide (postscript) can be found:

ANSWER From: (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: (Hale Landis)

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

QUESTION: What is FPT (Termination)?
ANSWER From: (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 
110 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 |---------------------------------* 2.8 V
     |________|       |                         |
          |           |                         |
        -----         |                         |
         ---          |                         \
          -           |                         /    term resistor
                      |                         \    (110 Ohms)
                      |                         /
                  ____|___                      |
                 |        |                     |
                 | Vreg 2 |-*--------* 2.4 V    |
                 |________| |        |          |
                            |      --+--        |
                            |       / \         |
                     +------+      /___\        |
                     |               |          |
                     |               |          |              terminated
                     |               *----------*------------- signal
                     |               |
                     |               |
                     |             --+-- 
                     |              / \
                     |             /___\   Both diodes are fast silicon
                     |               |     switching diodes (.6 V drop)
                  ___|____           |
                 |        |          |                 
                 | Vreg 3 |----------*  0.8 Volts

The diagram shows the circuit for terminating one signal. In a complete FPT
there would be 36 diodes and 18 110 Ohm resistors plus the regulator chips.
Using the values shown, transients would be clamped at 0.2V and 3.0V.

Some errors in the above diagram were corrected as suggested by
Wietze van Winden (

QUESTION: What is Active Termination?
ANSWER From: (Eric Smith)
        and (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

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

	   2.85 Volt Regulator
               +-----------+    +2.85V   110 Ohms
TERMPWR   -----| in    out |------+------/\/\/\/-------SCSI signal
               |   gnd     |      |
               +-----------+      |
                    |             +------/\/\/\/-------SCSI signal
                    |             |
GND  ---------------+             |
                                  +------/\/\/\/-------SCSI signal

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 (Brent R. Largent)

Typical passive terminators (resistors) allow signals to 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.

Active termination provide the following advantages:
- Helps reduce noise.
- A logic bit can be used to effectively disconnect the termination.
- Regulated termination voltage.
- SCSI-2 spec. recommends active termination on both ends of the scsi bus.
- Your Great New Jersey Web Sited resistance tolerences (from 1% to about 3%)

- Reduces current drawn from TERMPWR line.

In FPT form:
- Provides signal overshoot/undershoot clamping on all signal lines. ]

QUESTION: How can I tell whether an unmarked terminator is active or passive?
ANSWER From: Gary Field (
If you have an Ohm-meter of one kind or another, measure the resistance from
the TERMPWR pin to an adjacent GROUND pin. Reverse the probes and take another

If the reading is about 30.5 Ohms, with the probes both ways, you have a
passive single-ended terminator.

If the reading is about 45 Ohms, with the probes both ways, you have a passive
differential terminator.

Active terminators should read much higher and give very different readings
with the probes interchanged.

QUESTION: Where can I buy terminators ?
ANSWER From: Rodney Brown (
Info taken from Usenet postings by:
John Zatler (
Steve Schreppler (
Dave Nadler (

DataMate / Methode

Methode Electronics, Inc.
dataMate Division
7444 West Wilson Avenue
Chicago, IL  60656
(708) 867-9600
(800) 323-6858
(708) 867-3149 FAX

Brief description of terminators available.

Passive, Active, SLICK (Elaboration of FPT)) in:
Centronics 50 pin (SCSI-1)		DM8[05]0-09-[0RS]
Male 3 row D-Sub (Old Sun)		DM950-??-?
Male 50 position .050" Centres (SCSI-2 HD)	DM20[05]0-02-[0RS]
Male 68 position .050" Centres (SCSI-3 P cable)	DM2050-02-68[RS]
Male & Female for ribbon cables		DM1050-02-[0RS] (M)  DM650-06-[0RS] (F)
Male/Female for pass through between device and ribbon cable DM550-06-[0RS]

Newark Electronics stocks the DataMate product line
Newark's address info

Newark Electronics		(International orders)
4801 N. Ravenswood Ave.	        500 N. Pulaski St.
Chicago IL 60640-4496		Chicago IL 60624-1019
(312)-784-5100,	(FAX (312)-638-7652, TLX 6718690 NEWARK U).

Selectronix Ltd
Minerva House, Calleva Park,
Aldermaston, Reading, RG7 8NE, UK
Tel:    +44 (0)118 9817387
Fax:    +44 (0)118 9817608

QUESTION: What is Plug and Play SCSI?
ANSWER From: (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

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.


The Plug and Play specifications are now available via anonymous ftp at 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\*)   Clarifications and corrections to pnpisa.doc   MS-DOS testing tool to isloate ISA PnP hardware   Plug and Play device driver interface specification   Hardware spec for PnP ISA enhancement   Hardware spec for PnP ISA enhancement

  Plug and Play SCSI files (.\scsi_ide\*):  Plug and Play SCSI specification proposal     SCAM (SCSI Comnfigured Auto-Magically) specification

  Plug and Play BIOS files (.\bios\*):   Advanced Power management spec v.1     Plug and Play BIOS spec    Spec for optional method of storing config info for PnP BIOS

PlayList@Microsoft.COM alias:

There is an alias, PlayList@Microsoft.COM, 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 (

	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 (407) 869-6700 (main number)
                            (407) 862-4725 (fax)          (Columbia home web page)                 (Columbia e-mail)

[Update to above information 1/20/97][Editor(GF)]

From: "Alan L. Welsh" 
Subject: Western Digital 7000-Fasst SCSI Cards and CDP's SST software 
Alan L. Welsh, President
Columbia Data Products, Inc.

We don't usually recommend that users purchase the upgrade for the 7000
software today.  Development has ceased, Windows 95 is not supported except
in DOS mode, and today I would rather recommend a popular currently
manufactured Local-bus SCSI board and not an ISA 7000 board.  However,
there are still some companies that we do support that have standardized on
7000s and need to keep them in service for years to come.  So please buy
the software, sell the board, use it as-is, or buy a new board.



Starting in early 1987, Western Digital (WD) manufactured virtually all of
the  100,000+ 7000 SCSI boards, except for a few hundred that were made by
Future Domain.  The first few thousand, known as 7000-ASC boards went out
with no software and only a ROMBIOS that was actually written by John
Sponger of WD.  In the summer of 1987, Columbia Data Products (CDP)
completed and shipped its first ROMBIOS for the card that enabled it to
boot and operate in DOS.   At that same time CDP also completed a DOS
ram-resident driver so that DOS would recognize and operate the card
without the slowness of the ROMBIOS, a DASD driver so that DOS could access
additional drive letters and to break the (then) 32 meg barrier, and
partitioning software to perform the FDISK function for SCSI.  

It was CDP's goal at that time to develop and provide SCSI software that
would enable: any SCSI host adapter, to run any SCSI peripheral, on any
operating system, in any PC-based bus.  Since at that time WD had 80% of
the hard drive controller market, CDP chose WD as the most logical choice
to strategically market with, and so CDP supported their cards almost
exclusively.  During that following year, CDP continued to develop the
software for the 7000 host adapters, enabling it to run faster than any
other board of its time, including Adaptec's new 1540, whose hardware was
actually faster.  

In the fall of 1988, CDP exclusively licensed its SCSI software suite,
called SST to WD.  The WD 7000-asc SCSI host adapter was renamed
7000-FASST.  WD was the first OEM to ship software with all SCSI boards
distributed as part of the package.  CDP's SST software was well received,
even though SCSI was still a relatively small market.  CDP was paid a
royalty for each card shipped and CDP provided complete software support
and limited hardware support throughout the world.  

By 1991 CDP had developed support for all SCSI peripherals known, all PC
operating systems such as Unix, Xenix, Windows, Dos, Netware, and even AIX,
although never officially released, and a SCSI toolkit utility package.
All of the 7000-FASST's shipped had multiboot capability that allowed all
of these operating systems to simultaneously coexist on a single hard drive
so that one OS can be selectively booted each session.  

CDP's exclusive was ending with WD, and CDP was porting the software to 25
of the most popular SCSI host adapters.  Unfortunately, most of software
had to be rearchitected and rewritten to embrace not only all the new
adapters but also the new SCSI software standards such as CAM, LADDR, ASPI,
INT-4b, as well as CDP's own standard since 1987, SDLP.  During the next
few years WD was losing a considerable amount of money and sold many of
their product lines, which included selling the SCSI board business to
Future Domain.  Future Domain did very little sales of the 7000 as they had
competing product lines and didn't understand the value of a bus mastering
SCSI board.  (Bus mastering gives the card the ability to move data to and
from the card and system memory directly without the CPU's involvement,
making it as fast as the peripherals driving it, even on an old slow
80286!)  The bus mastering 1542 product line from Adaptec is still being
produced today, very popular, and is based on the same basic design as the
7000.  From a pricing standpoint, the prices for this class of product has
declined less than 50% in ten years.  This is only amazing if you compare
the price of 1MB of memory at $300 in 1987 to that of today. 

CDP has continued to develop and support for the 7000-FASST continuously,
even though the board hasn't been manufactured for quite a number of years.
 Our last major revision of our SST-IV software was done in late 1993,
although there have been some minor revisions since then.  To enable CDP to
continue to develop software and support the board, CDP has been selling
upgrades to the large installed user base for years.  Without this revenue,
development and support would have ceased long ago.  There are no plans to
continue development at this time, as SCSI is moving from the ISA bus to
Local Bus.  Although Window-95 development and support was considered, the
potential upgrade business wouldn't have covered the cost of development.

In 1994 CDP entered the server backup software market, shipping the first
version of Snapback in March of that year.  Many of our customers for years
had been begging us to write our own backup software and were complaining
that "restoring" their servers sometimes took days with the current backup
products.  For SCSI software development purposes only, CDP had been
backing up and restoring hard drives containing multiple operating systems
for years.  CDP adapted and then rewrote this software in this first
release to provide the ability to backup and restore any hard drive that
contained any operating system, from DOS.  CDP later wrote a device driver
in Netware, that could make the backup tape look, act and perform like a
hard drive from a Netware workstation.  This enabled direct file retrieval
and use through Netware from the backup tape, making it appear to a
workstation to be just another drive letter.  Since all the directories and
FATs are cached, the tape is almost as fast as a hard drive.  Another
feature, resize, allows a Netware server's hard drive to be replaced with a
larger one in an hour instead of a day's labor.

At fall COMDEX 1996, CDP released its latest version, Snapback Live! that
backs up a live image of a Netware file server's hard drive, capturing all
open files in the process, without impacting system performance.  Watch
your Computer magazine for Snapback reviews in 1997, as well as a version
for NT.  Innovating backup software has now become CDP's new life--from an
innovative SCSI software company.

For more information, contact us at: OR

QUESTION: What if I have a SCSI drive larger than a gigabyte (1024MB) ?
ANSWER From: Gary Field (
The IBM PC/AT BIOS Int 13h disk interface was specified in about 1986 when
a large disk drive was about 60 MB. IBM decided that disks wouldn't have
more than 1024 cylinders and only allocated 10 bits for the CYL parameter
to the INT 13h interface. By 1989, this was already a problem. When vendors
began to support SCSI drives under INT 13h, they needed to come up with a
translation algorithm between the CYL, HEAD, SECT parameters of INT 13h and
the linear block numbers used by SCSI devices. Various vendors chose to
map the two such that each INT 13h "cylinder" contained 1 MB.
In other words they emulated a drive with 32 heads and 63 sectors per track.
At the time, large drives were at about 300 MB, so this worked OK. Once drives
larger than 1024 MB arrived, a problem developed. They couldn't provide
cylinder values greater than 1023! Changing algorithms became necessary.
This is painful since any disk formatted with the old algorithm can't be read
using the new algorithm.
By the way, different vendors chose different mappings, so drives formatted
with one adapter can't necessarily be moved to a different one.
Adaptec's newer adapters (e.g. the 154xC and the 154xCF) provide a BIOS control
to select the old algorithm or the new one, and they also provide BIOS PROMs
for the 154xB that will use the new algorithm.
There is an absolute limit of 16 M sectors which means 8 GB assuming 512 byte
sectors. Also DOS only allows 2 GB per partition. 
The day when this presents another problem is not too far away (1995?)
Hopefully, we'll all be running more sophisticated O/Ses that bypass this
limitation by then.

QUESTION: My SCSI bus works, but is not reliable. What should I look at?
ANSWER From: Gary Field (
If you still have problems after you're sure that you have all the ID and
termination and cable issues resolved, it's time to dig a little deeper.
If you get your SCSI bus to the point where it basically works, but it isn't
reliable I have found that the gremlin can be the TERMPWR voltage.

With your system fully powered up, and both terminators attached, measure
the TERMPWR voltage at the far end of your bus. It needs to be between 4.25
and 5.25 Volts. Many vendors start with the system's +5 VDC and add a regular
silicon rectifier diode and fuse in series. Silicon rectifiers have an
inherent voltage drop of .6 to 1.0 Volts depending on the current through them.
Schottky barrier rectifiers are much better for this application. I always use
a 1N5817 myself. If the diode on the host adapter is a 1N400x type, change it
to a 1N5817. If you add up the drop across the diode and the fuse and 15 feet
of ribbon cable and the connector contact resistances, many times you'll
find yourself below 4.0 Volts. When using passive terminators, this can
shift the signal threshold and decrease the signal to noise ratio on the bus.
If you aren't able to get relief with these methods, sometimes you can solve
the problem by having several devices supply TERMPWR to the bus.

Sometimes the voltage is high enough, but there is too much noise on the
TERMPWR line. This can cause really strange problems! If you can see more than
about 200 mV of noise on TERMPWR, add a .1 uF and 10 uF capacitor from TERMPWR
to one of the adjacent GROUND lines. You need to have the bus as active as
you can get it when measuring the noise. I have actually seen over 1 Volt of
noise in some severe cases.

Another way you can help to solve TERMPWR problems is to use active
terminators. These don't draw as much current from the TERMPWR source and they
also have a built in regulator which can operate on lower voltage than the
standard passive terminators. The regulator also tends to reduce the noise.

QUESTION: Where can I find information about programming using the ASPI
          interface from DOS and Windows?
ANSWER From: Gary Field (

The Adaptec BBS has some documents about ASPI. They also have a WWW server.
See the FAQ Question "How can I contact Adaptec?" for phone numbers and URL
information etc.*

Dr Dobb's Journal March 1994 issue pg 154, has an article called "The Advanced
SCSI Programming Interface" by Brian Sawert. Example code in C and x86
assembly language is included. The code can be obtained via anonymous ftp
from: /pub/ddj/1994.03/

QUESTION: How to replace Macintosh internal HD and terminate the SCSI chain
Answer From: Jie Yuan PhD (Jie.Yuan@UC.Edu)
   The factory installed Macintosh internal HD should be terminated.
   Make sure the terminator/resitor-package is installed in the drive
   before using it.  Most vendors will install the terminator for you
   if you tell them it is for use in Macintosh as the system disk.
   Manufacturers usually have toll free numbers for SCSI termination,
   ID, and such.  
   If you don't already have the terminator, they may send you one 
   for free.
   BTW, Macintosh SCSI chain starts at the system disk (ID=0),
   and ends at the control board (ID=7).  ID numbers from 
   1-6 should be used for any other divices on the chain.

QUESTION: Will attaching a SCSI-1 device to my SCSI-2 bus hurt its performance?
ANSWER From: Gary Field (
Attaching a SCSI-1 device to a system with a SCSI-2 host adapter and several
SCSI-2 devices already attached will not hurt over-all performance
significantly unless it doesn't handle disconnect/reconnect well. This 
assumes that the host adapter keeps track of protocol options seperately
for each target device. Some people have the idea that attaching a SCSI-1
device to a SCSI-2 bus will cause the entire bus to run at SCSI-1 speeds.
This is not true.

QUESTION: Can I connect a SCSI-3 disk to my SCSI-1 host adapter?
          Can I connect a SCSI-2 CDROM to a SCSI-3 host adapter?
	  Can I connect a Narrow SCSI2 disk to a WIDE SCSI3 host adapter?
ANSWER From: Gary Field (
Questions of this nature really cannot be answered in a useful way.
There are so many aspects and options to each of the SCSI standards,
you need to be much more specific about what devices and adapters
you're interested in connecting. Most of the time the best thing to
do is just try it! Most combinations will work, but if you're considering
a purchase and looking for a guarantee from "The Net", forget it.

The issue is further complicated by the fact that vendors like to latch
onto the latest acronyms before they even know what's involved.
For example SCSI3 is not approved yet, but vendors are already
saying their devices are SCSI3 compatible. Since there is no standards
compliance testing organization, they can pretty much say what they want.

If you buy a high end host adapter (probably called SCSI3 :-) ) from a
reputable vendor, and it has enough control over the various options
(like synch xfer rate 5,10,20 xfers/s and the ability to disable WIDE or
FAST/Ultra negotiation), and you carefully think out what devices you connect
to it (all WIDE devices nearest the host adapter end of the bus etc.),
and you are careful to properly terminate not only both ends, but both
halves (upper byte and lower byte) of the bus, and none of the older devices
you might already have (like a Panasonic CDROM) do anything stupid (like not
handle the WIDE negotiation message without hanging) then it will all work
fine. :-)

Even though a host adapter may be called SCSI3 doesn't mean it can
enable or disable each optional feature, yet this is vital for supporting
older devices.

To make matters worse, you won't know which older devices do some of the
stupid things unless you know someone who's been bitten already.
Your best bet is to look for good deals on name brand devices and adapters
and before you buy, ask in comp.periphs.scsi whether anyone has tried
the combination you're considering. It's also important to buy from a
well known vendor with reasonable return policies.

If you're looking at buying a Vendorxyz spiffydisk which claims to be
SCSI-3 compatible and you have a Seagate ST-01 host adapter and you want to
know if anyone else has tried this combination, then that's exactly what you
should ask.

In general, most SCSI devices and adapters made less than 4 years apart
will probably work together, but without specific information about exactly
which devices there's no assurance of it. There's also the potential for
poor performance even if it does work.

QUESTION: Can I connect a WIDE device to my narrow SCSI host adapter?
QUESTION: Can I connect a narrow device to my WIDE SCSI host adapter?
ANSWER FROM: Gary Field (

Yes, you just need an appropriate adapter. Most WIDE devices use the
68 pin "P" connector so you need a 68 pin to 50 pin adapter.
You do need to make sure that both the upper byte and lower byte of the
bus will be properly terminated though. Some adapters provide a place
for terminators, others do not. If the wiring adapter is placed right at
the SCSI host adapter, you can usually configure the host adapter's
on-board terminators to only terminate the high byte. You need to
be clear on what type of connectors are present where you want to
do the conversion. You also need to plan your bus so that all the WIDE
devices will be at one end and all the narrow devices will be at the
other end. Certain host adapters with auto-termination make the
assumption that when the low byte is terminated the high byte is
also. When using WIDE/narrow adapters this assumption is not valid.

Such adapters are available from:

Technical Cable Concepts
1790 E. McFadden Ave.
Unit 103/104
Santa Ana, CA 92705
TEL: (714) 835-1081
FAX: (714) 835-1595

2201 Pine Drive
Dickinson, TX 77539
Order Line 800-786-1157
Fax Line (281)534-6580
Main Line (281)534-3919

Dalco Electronics
P.O. Box 550
275 South Pioneer Blvd.
Springboro, OH 45066-1180

QUESTION: How does device ID numbering work with WIDE vs NARROW devices?
ANSWER From: Gary Field (

Narrow SCSI devices can only use IDs 0 through 7. WIDE SCSI devices on
a SCSI-3 system with 68 pin P cables, can use IDs 0 through 15. It is
generally wise to reserve 0-7 for narrow devices though.
SCSI-2 only specified the use of IDs 0-7 even for WIDE devices, but SCSI-3
allows 0-15 for WIDE devices. All devices on one bus must have unique IDs
of course.
The arbitration priorities are as follows:
ID 7
ID 0
ID 15
ID 8
ID 23
ID 16
ID 31
ID 24

A WIDE device that is set to ID 10 knows not to respond to selection
for ID 2 because the parity bit P1 (for  bits 8-15) will not be set
by the initiator. During a selection of ID 10, the P parity bit
(for bits 0-7) will not be set by the initiator, but the P1 bit will be.

--/* Gary Field - WA1GRC, Digital Equipment Corp., 110 Spit Brook Rd
     M/S ZKO3-3/T79, Nashua, NH 03062-2698, phone: (603) 881-2543
     email:  TZ=EST5EDT


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