Xref: utzoo comp.sys.mac.misc:3736 misc.forsale.computers:1588
Path: utzoo!attcan!uunet!snorkelwacker!husc6!encore!wcarroll
From: wcarroll@encore.com (Mr. New Dad)
Newsgroups: comp.sys.mac.misc,misc.forsale.computers
Subject: Re: 170Meg Wren Hard Drive for sale (SCSI)
Message-ID: <128645@jake.encore.com>
Date: 1 Oct 90 16:44:48 GMT
References: <1990Oct1.002316.4297@cunixf.cc.columbia.edu>
Organization: Encore Computer Corp, Fort Lauderdale, FL
Lines: 39

From article <1990Oct1.002316.4297@cunixf.cc.columbia.edu>, by liggio@cunixf.cc.columbia.edu (Vincent J. Liggio):
> 
> Only problem with that is that it is not SCSI-2 compatible, nor do the
> drives do synchronous transfers.  This limits the drive's transfer speed
> and it will be going out with the SCSI-1 specs.  Only Wren series V- do
> synchronous transfers, and the only drives so far that are SCSI-2 are
> Quantum drives, and they are hard to find because of their demand (large
> backorders).  SCSI-2 should do up to 5 Mb/sec (yes, megabytes) at its peak
> speed with the proper controller.

Nice points, but do they mean anything here? Do any products in the
Macintosh line do synchronous transfers? I know that none would be
considered SCSI-2. How many of the products in the Macintosh line
can outrun an asychronous drive at ~1 Mbyte/sec?

Fast drives are nice, but they require fast controllers. And don't
believe every marketing brochure you see. Just because you have a
drive that's advertised for 5 MB/s and a controller that's advertised
at 5 MB/s doesn't mean you can plug them together and they will run
at 5 MB/s.

And is transfer speed even the correct parameter to look at? Let's look
at a drive with an average access time of 20 ms. At 1 MB/s, 20 ms is
used for 20 kB. At 5 MB/s, that's 100 kB. If your typical disk access
is <= 5 kb, you're spending more time looking for the data than moving
it from the disk.

And to be picky:

All synchronous drives will also transfer asynchronous. It's required.

And SCSI-1 will do up to 5MB/s. SCSI-2 will (someday, maybe) do up 
to 40 MB/s.


-- 
William R. Carroll  (Encore Computer Corp., Ft. Lauderdale FL)
wcarroll@encore.com         uunet!gould!wcarroll
"The brain-dead should not be allowed to operate motor vehicles!" - Me