Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!evax!utacfd!merch!cpe!adaptex!adaptx1!neese
From: neese@adaptx1.UUCP
Newsgroups: comp.periphs.scsi
Subject: Re: SCSI vs. SCSI II
Message-ID: <283400093@adaptx1>
Date: 5 Apr 91 07:55:26 GMT
References: <1674@aut.autelca.ascom.ch>
Lines: 30
Nf-ID: #R:aut.autelca.ascom.ch:1674:adaptx1:283400093:000:1434
Nf-From: adaptx1.UUCP!neese    Apr  3 16:54:00 1991


>/* ---------- "SCSI vs. SCSI II" ---------- */
>What's the difference between SCSI and SCSI II ?
>
>Is it only the higher speed?

SCSI-1 did not define commands for device types such as CD-ROM, Mag-Opt,
Printer, Communications, Processor, nor tape very well.

So SCSI-2 does and SCSI-3 will do it better.

There is no perfromance to be gained with SCSI-2, unless the device supports
the optional FAST SCSI-2 spec.  And even then, there may be no performance
to be gained as anything that can negotiate for speeds less than 200ns
is to be considered FAST SCSI-2.  So if a device negotiates for 190ns
periods, it is considered FAST SCSI-2 even though it is only running at
5.2MB/sec instead of 5.0MB/sec.  Thene there is the real issue,..........
sustained data rates.  Something you normally find out *after* you buy
the device.  It is usually not specified in the device flyers and for most
manufacturers, it is quite wise.  As a matter of fact, the only drive 
manufacturer I know that actually states the sustained data rate, is Imprimis
and only on the Elite series.  They have a right to brag about it as they
claim a sustained rate of 4MB/sec.  Probably the fastest SCSI drive around.
I should have one in my hands in a few days and will make further comment
on it if this proves to be false.

			Roy Neese
			Adaptec Senior SCSI Applications Engineer
			UUCP @  neese@adaptex
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