Ultra-2 SCSI

John Lohmeyer john.lohmeyer at symbios.com
Fri Apr 3 10:44:29 PST 1998

* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* John Lohmeyer <john.lohmeyer at symbios.com>

All of the T10 Committee draft standards can be found on the T10 Web site at:


I recommend that you also visit the SCSI Trade Association's web site at:


SCSI keeps evolving, particularly at the hardware level.  The hardware
generations are:

Name    date        ANSI designation Comments
------- ---------- -----------------
SASI    circa 1981 (now obsolete)    Asynchronous data transfers only ~ 1.5
SCSI    1986       (now obsolete)    Up to 5 MByte/sec
SCSI-2  1994       X3.131:1994       Up to 10 MByte/sec on using
differential drivers
SPI     1995       X3.253:1995       Up to 10 MByte/sec plus wide SCSI
(a.k.a., SCSI-3)
Fast-20 1996       X3.277:1996       Up to 20 MByte/sec (a.k.a., Ultra SCSI)
SPI-2   current draft standard       Up to 40 MByte/sec (a.k.a., Ultra2 SCSI)
SPI-3   newly-approved project       Up to 80 MByte/sec (probably will be
called Ultra3)

The above table grossly over simplies a number of things.

SPI-2 introduces an new driver/receiver type called Low Voltage
Differential (LVD).  It enables the higher data rates.  Many new products
support both LVD and the older single-ended drivers/receivers.  These
products are called multi-mode or universal.

SPI-3 is the gleam in the standards committee's eye.  We do not yet have a
first draft of SPI-3.

i hope this helps!

John Lohmeyer, Chair T10 Technical Committee

At 4/2/98 09:10 AM, you wrote:
>* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
>* Andreas Koch <koch at aimnet.com>
>Hi all,
>Please pardon my total ignorance, but would anybody be so kind to take a
>moment and explain to me briefly what the differences are between Ultra-2
>SCSI and SCSI-2/3 and where I could find the standard spec. (I could only
>find SCSI-2 related documents on ansi.org).
>Andreas Koch
>koch at aimnet.com

John Lohmeyer                  Email: john.lohmeyer at symbios.com
Symbios, Inc.                  Voice: +1-719-533-7560
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Colo Spgs, CO 80907              BBS: +1-719-533-7950

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