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From: grr@cbmvax.UUCP (George Robbins)
Newsgroups: comp.arch
Subject: Re: Disk Striping (description and references) plus class brief
Message-ID: <2240@cbmvax.UUCP>
Date: Fri, 21-Aug-87 07:42:30 EDT
Article-I.D.: cbmvax.2240
Posted: Fri Aug 21 07:42:30 1987
Date-Received: Sun, 23-Aug-87 01:18:33 EDT
References: <2432@ames.arpa> <3721@well.UUCP>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 35

In article <3721@well.UUCP> rchrd@well.UUCP (Richard Friedman) writes:
> 
> One more comment about disk striping:  there is a real limiting
> factor to disk technology, and it is not the speed of light (the
> limiting factor to CPU technology) but rather the speed of sound.
> If you try to make a disk go too fast in an attempt to improve
> transfer rates, you approach Mach 1 in the turbulent flow around
> the surface of the disk, and the resulting shock wave destroyes
> the disk, literally.

Yeah, but my calculations indicated that a 14" drive has a peripheral
velocity of "only" 150 miles/hour.  If this turbulence/mach 1 thing
was currently a limiting factor, we could have some of these new 8"
drives spinning 8 times as fast, no?

There may well be some head/media engineering problems associated with
going faster, but the limiting factor has traditionally been in the
head magnetics and drive electronics coupled with limited i/o bandwidth
on the systems that constitute the volume uses of the drives.

Now, as others have pointed out, parallel transfer drives are available,
from Fujitsu and new CDC.  They aren't cheap, because the volume is much
lower and you need n times the drive electronics in the read/write path
as there is usually only a "preamp" associated with each head, then common
amplification, shaping, data-separation circuitry in normal drives.  Also
I imagine you need some bit-deskew logic to insure that the right bits
really come out in parallel.

Now I'm sure Fujitsu could have made the drive spin some percentage faster,
but in doing so, the would have lost much of the parts interchangability
with their volume drives, which would only make things even more expensive.
-- 
George Robbins - now working for,	uucp: {ihnp4|seismo|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)