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From: jlw@mtuxo.UUCP (J.WOOD)
Newsgroups: comp.arch
Subject: Re: Disk Striping (description and references) plus class brief
Message-ID: <505@mtuxo.UUCP>
Date: Thu, 13-Aug-87 17:50:52 EDT
Article-I.D.: mtuxo.505
Posted: Thu Aug 13 17:50:52 1987
Date-Received: Sat, 15-Aug-87 10:51:35 EDT
References: <2432@ames.arpa> <3721@well.UUCP> <2838@phri.UUCP>
Organization: AT&T, Middletown NJ
Lines: 21


Disks cannot be put in a vacuum using current thinking since
the heads literally fly along the surface of the disk.  This
requires air molecules since the head shape is like an inverted
airfoil.  The head tries to fly into the disk.  Then when it gets
microscopically close ground effects take over and keep the head
from actually crashing into the disk surface (most of the time :-) ).
If this technology were to be abandoned in favor of say physical
rigidity holding the heads at the proper distance, then the tolerances
would mean that the gap would be much larger leading to a severe
loss of disk capacity since this closeness between head and
surface is what allows us to write such a thin strip of data
on the disk without interfering with adjacent tracks. Wider tracks
would also increase track to track access time.  Unless a substitute
for air could be found like the suggested Hydrogen or some
other mechanism like superconductor repulsion to get the
heads close to the surface without actually crashing, this looks
like a losing proposition.

Joe Wood
lznv!jlw