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From: liggio@cunixf.cc.columbia.edu (Vincent J. Liggio)
Newsgroups: comp.sys.mac.misc,misc.forsale.computers
Subject: Re: 170Meg Wren Hard Drive for sale (SCSI)
Message-ID: <1990Oct1.231629.20713@cunixf.cc.columbia.edu>
Date: 1 Oct 90 23:16:29 GMT
References: <1990Oct1.002316.4297@cunixf.cc.columbia.edu> <128645@jake.encore.com>
Organization: Columbia University
Lines: 45


In article <128645@jake.encore.com> wcarroll@encore.com (Mr. New Dad) writes:
>
>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?

Well, I was commenting on the Wren IV from Mr. Zamost, which is along the
PC line (unless you get cases, I suppose).  The PC line is faster than 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.

Of course not, but then again there are combinations that will.

>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.

With drive caching, this should not be a problem, because the data should
be in the cache already (depending upon the application you are using,
and other factors....)

>And to be picky:
>
>All synchronous drives will also transfer asynchronous. It's required.

Of course everything is a subset of the older stuff, for compatability
reasons.  But an asynchronous controller won't add anything for a
synchronous drive as speed goes.

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

I hope so.


Vince