What's a SCSI-1, SCSI-2, SCSI-3, etc.?
Arctic Vortex
What is SCSI-1?
What is SCSI-2?
What is SCSI-3?
What is Fast SCSI?
What is Ultra SCSI?
What is Wide SCSI?
What is Ultra Wide SCSI?
What is Ultra2 SCSI?
What is 50-pin SCSI?
Whta is 68-pin SCSI?
Are there SCSI's with different number of pins?
Can you have multiple SCSI cards in one computer?
Thanks.
SpamShield-...@usa.net
Please remove the preceeding "SpamShield-" to send email. Thanks.
Benjamin D Verzosa
at www.adaptec.com
Adaptec is the industry leader in SCSI cards and therefore not only
will you find pertinent information, you will also learn about the current
and most accpected controllers on the market.
Albert
Arctic Vortex wrote in message <35d6e...@news.auhs.edu>...
Arctic Vortex
Adaptec is not in the business of educating/informing technical knowledge.
Benjamin D Verzosa wrote in message <6r7irv$r23$1...@owl.slip.net>...
Roger J.Hamlett
>
> Where can I get info on SCSI?
>
> What is SCSI-1?
> What is SCSI-2?
> What is SCSI-3?
> What is Fast SCSI?
> What is Ultra SCSI?
> What is Wide SCSI?
> What is Ultra Wide SCSI?
> What is Ultra2 SCSI?
> What is 50-pin SCSI?
> Whta is 68-pin SCSI?
> Are there SCSI's with different number of pins?
> Can you have multiple SCSI cards in one computer?
big question to answer fuly. Most of the data _is_ on the Adaptec
site, but the Symbios site is better in terms of having the data in a
form that 'answers' your questions.
Basically SCSI has evolved, with more sophisticated commands in the
'language', increases in speed, and the use of more wires to increase
data rate yet further. SCSI-1 is the 'original'. SCSI-2, is a set of
extensions, including as one option a faster rate (Fast SCSI). This
also included a 'wide' option (twice the number of data wires), but
using two cables. This form never took off, and instead manufacturers
started to produce their own wide variant using a single 68pin
connector. This is ratified in the SCSI-3 proposals. SCSI-3 is a
'generic' term to cover another load of extensions beyond SCSI-2,
some of which have been ratified, but others are still in discussion.
The main ones in 'current' release, are the wide connector, and the
use of higher data rates still (20MHz). This faster data rate, is
often referred to as 'ultra'. Hence an 'ultra' bus gives 20MB/sec
(less command overhead), and a 'ultra wide', gives 16bits at a time
at the same rate, giving 40MB/sec. The only 'problem' with these
faster rates, is that the signalling can start to become unreliable,
and hence the 'recommended' cable lengths are a lot shorter
(sufficiently so, to make wiring difficult in a lot of systems). So
beyond your list there is yet another 'speed' called 'ultra 2', that
uses a different signalling standard (LVD - Low voltage
differential), to get round these problems, and allow a wide bus to
handle 80MB/sec. All the earlier standards are 'reverse compatible'.
What happens is that the devices 'talk' to each other across the bus
at the slowest SCSI data rates, and agree between themselves what
speeds they can turn 'up' to. Hence an 'ultra' device will run fine
with a SCSI-1 controller, or an ultra device and controller can
co-exist on a bus with a SCSI-2 device, with the speed of the bus
turning up when the ultra devices are talking, and down again when
the slower device is in use. LVD is the exception to this 'reverse
compatibility' , in that though it is designed so that attaching a
SCSI-2 device will cause no problems, once such a device is attached,
the whole section of the bus has to revert to the older (and slower)
signalling standard. To avoid this causing a problem the Adaptec
controllers using this standard, have a 'transceiver' chip that
seperates the bus into two halves, and allows the 'LVD' devices to be
kept seperate from the older slower devices. The original 'narrow'
bus, uses 50 pins, and the 'wide' variant uses 68pins. A wide bus,
will happily talk to a narrow device, with a suitable 68-50 adapter,
but termination has to be carefully arranged.
Yes you can have multiple cards, or single cards with multiple
busses.
Good Luck
--
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Jerry Leslie
: Where can I get info on SCSI?
: What is SCSI-1?
: What is SCSI-2?
: What is SCSI-3?
: What is Fast SCSI?
: What is Ultra SCSI?
: What is Wide SCSI?
: What is Ultra Wide SCSI?
: What is Ultra2 SCSI?
: What is 50-pin SCSI?
: Whta is 68-pin SCSI?
: Are there SCSI's with different number of pins?
: Can you have multiple SCSI cards in one computer?
There's a SCSI FAQ, available at:
http://www.cis.ohio-state.edu/hypertext/faq/usenet/scsi-faq/
http://www.ultranet.com/~gfield/gary/scsi.html
http://fieldnet.ne.mediaone.net/gary/scsi.html
--Jerry,
Jerry R. Leslie jerry....@aspentech.com Aspen Technology, Inc.
(my opinions are strictly my own)