Managers,
Here's my summary about SCSI cable differences. I'm late with this summary
because of the holidays and because our company has been moving lots of
people, machines, and laboratories to a new building. (Also because I'm
a well practiced procrastinator :-)
There was a lot of information about SCSI specifications but I've summarized
only the cable information I requested. If you want the complete concatenation
of the replies, please request it personally. (1700 lines, 74 KB)
Based on the number of "please summarize" requests received, I was relieved to
discover that I was not the only SCSI illiterate reading this newsgroup.
Thanks to the many, who provided information.
- daryl -
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ORIGINAL QUESTION:
Managers,
Since our Sun system is a mixture of Sun and 3rd party devices I need to
make sure that I have the proper mix of devices and cables. I admit my ignorance of SCSI devices since I've been dealing mostly with SMD and IPI type systems with a few simple SCSI devices here and there.
I've seen discussions in this net group recently that mention SCSI-1, SCSI-2,
and SCSI-3 cables. I've also seen some vague references in some Sun device manuals warning one to be sure to use the proper cable. Could someone please educate me to the differences?
I know that SCSI has evolved over the years and that there is (I believe) at least two versions of the SCSI bus specifications (SCSI-1 and SCSI-2 ?) and that recently SCSI devices capable of synchronous data transfer have become popular, However lets try to keep this discussion restricted to the cable differences and requirements and not digress into the details of the bus specifications or advantages/disadvantages of the devices themselves.
In which FM are SCSI cable differences detailed?
How can one tell the difference visually?
Can one assume that all cables are simple straight-through, pin-to-pin
connections, or are there any unusual pin configurations?
Do all SCSI cables have exactly 50 wires, or do I have to watch out
for missing wires?
The following is a list of the physical description of the various types
of SCSI connectors that I know about. What is the "proper" nomenclature
for the different types of SCSI connectors? Are there more?
3-row, 50-pin "D" connector similar to a "standard" RS-232 "D" connector
but larger.
50-pin, "Centronics" type connector
2-row, 50-pin miniature "D" conector
50-pin, 2-row ribbon connector
If there is no Sun manual that defines SCSI and the cable types, then
is there a 3rd party book that is worth recommending?
Since there are so many different types of connectors, there has arisen
an industry to provide conversion cables to connect device A to device B.
Is there a "standard" way of knowing what to specify, or how to specify
to a vendor your cable/connector requirement so that when the device
arrives that it is immediately attachable?
I've been watching this net for a while and have not seen this discussed
before. If I've missed a summary or if this is painfully obvious I'll slink
away, and lick my wounds, otherwise I'll summarize for the rest of us SCSI
illiterates. :-)
Daryl Crandall
The Mitre Corporation
daryl@mitre.org
(703) 883-7278
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MY SUMMARY:
No one identified any Sun manuals where SCSI cable differences were discussed.
All respondents seemed to agree that a SCSI cable is a SCSI cable and any
differences in SCSI operation are due to the devices they are attached to.
One CAN assume that all SCSI cables for all real computers (which excludes
Macintosh and Amiga) are 50 wire, straight-through connections.
("Mac's use 38 wires"; "Amiga use 25 wires!!??")
Many respondents indicated that there is no standard nomenclature for the
connector types but the following nomenclature is quite common:
DB-50: 3-row, 50-pin "D" connector similar to a "standard"
RS-232 "D" connector but larger.
CENTRONICS: 50-pin, "Centronics" type connector
Mini-D: 2-row, 50-pin miniature "D" conector
ribbon connector: used internally within a shielded chassis
A physical description of the connector(s) in addition to the "name" would
clarify your needs when ordering cables from a vendor.
Here's what I learned about SCSI standards:
As far as the cables are concerned, there is no difference between a SCSI-1,
and a SCSI-2 cable. SCSI-3 is a new standard that is being developed and
there is some discussion that the characteristic impedance of the cables and/or
termination chips will change. This could cause problems with mixing SCSI-1
and SCSI2 devices with SCSI-3 devices. However, there is also talk that
dynamic termination circuits may circumvent this problem. Don't rely me for
the definitive word on this, but keep your ears open.
The "Centronics" type connector is often refered to as the "standard" SCSI
connector and was originally used with SCSI-1 systems. However, Sun decided
to use the DB-50 connector instead.
The "mini-D" connector is often associated with the SCSI-2 standard, but
several respondents indicated that Sun has not implimented the full SCSI-2
standard in their products yet and their use of the "mini-D" connector is
only a "real-estate" decision. due to the small size of their CPU boxes.
I had a couple of replies that indicated that Sun does define it's cables
but there was no indication of which FM it's located in. That's like asking
where can I find the whole quote "To be, or not to be..." and getting the
answer "the library". :-)
Here's a book that was mentioned by some kind person.:
"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."
This archive was generated by hypermail 2.1.2 : Fri Sep 28 2001 - 23:06:33 CDT