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From: jxc@rayssd.UUCP (Jeffrey J. Clesius)
Newsgroups: net.micro
Subject: Re: Re: This is serious?
Message-ID: <996@rayssd.UUCP>
Date: Wed, 21-Aug-85 12:51:10 EDT
Article-I.D.: rayssd.996
Posted: Wed Aug 21 12:51:10 1985
Date-Received: Sat, 24-Aug-85 15:04:02 EDT
Sender: jxc@rayssd.UUCP (Jeffrey J. Clesius @ Raytheon Co., Portsmouth RI)
Distribution: net
Organization: Raytheon Co., Portsmouth RI
Lines: 33

> Inertia rears its ugly head in yet another way.  I used to have access to a
> MODCOMP III with the OS on a fixed-head disk.  We'd use the machine with no
> trouble at all through the week, but the thing would invariably fail to boot
> on Monday mornings.  One Friday someone got the bright idea to turn off the
> disk, and Monday we ran it back up and the system booted fine.  We finally
> figured out that the problem was inertia, in the guise of centrifugal force;
> as long we we read and wrote things often enough, the bits didn't have time
> to be thrown off the disk, but over the weekend was too long.  We had to
> install a bit bucket under the disk drive to keep the computer room clean.
> 
> Cheers,
> Dick Binder   (The Stainless Steel Rat)

We had a similar problem whose solution worked to our advantage.  To avoid
the loss of bits off the edge of the disk, we installed a raised edge on the
circumference.  What we found was that the tracks were migrating over time
toward the outside of the disk.  Once we had installed a logarithmic track
seeking algorithm as part of the disk driver, we found that the capacity of
the disk was increasing steadily by about 10% per week.  The hardest part
about the track mapping algorithm was to allow for loss of migration while
the disk was not spinning due to downtime.

-- 
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