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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.arch
Subject: Re: Disk Striping (description and references) plus class brief
Message-ID: <8412@utzoo.UUCP>
Date: Fri, 14-Aug-87 14:33:57 EDT
Article-I.D.: utzoo.8412
Posted: Fri Aug 14 14:33:57 1987
Date-Received: Fri, 14-Aug-87 14:33:57 EDT
References: <2432@ames.arpa> <3721@well.UUCP>, <2838@phri.UUCP>
Organization: U of Toronto Zoology
Lines: 20

>	So, why not put the disk in a vacuum?

Because when the books says that the heads "fly" above the disk surface,
it is being literal and not metaphorical.  The separation between heads
and surface is maintained aerodynamically, not mechanically.  So there
has to be some sort of gas around.

> 	I understand that in big power plants, the insides of the
> generators are filled with hydrogen instead of air because the speed of
> sound is faster so the rotor tips don't go supersonic...

This would probably work, perhaps with some design changes in the head
aerodynamics, but the explosion hazard would be much more serious in a
mass-produced quasi-consumer product that has to run safely (if not
necessarily reliably :-)) in the field for years without maintenance.
Big power plants can afford significant continuous effort to keep such
problems under control.
-- 
Support sustained spaceflight: fight |  Henry Spencer @ U of Toronto Zoology
the soi-disant "Planetary Society"!  | {allegra,ihnp4,decvax,utai}!utzoo!henry