Path: utzoo!attcan!uunet!van-bc!
From: lphillips@lpami.wimsey.bc.ca (Larry Phillips)
Newsgroups: comp.sys.amiga
Subject: Re: <None>
Message-ID: <1976@lpami.wimsey.bc.ca>
Date: 14 Sep 90 22:18:37 GMT
Lines: 29
Return-Path: <lpami!lphillips>
To: van-bc!rnews

In <1990Sep14.163643.20618@psuecl.bitnet>, d6b@psuecl.bitnet writes:
>In article <1966@lpami.wimsey.bc.ca>, lphillips@lpami.wimsey.bc.ca (Larry Phillips) writes:
>> Since we are picking nits, I'll pick this one. The Amiga does indeed have
>> hardware support for GCR in at least one way. See page 243 of the Hardware
>> Reference Manual, where you set Precomp for MFM or GCR. Agreed that the actual
>> encoding/decoding needs to be done in software.
>
>Ah, a perfect opportunity to ask: What IS precompensation?
>I read a description once but it was totally incomprehesible and probably
>wrong.

Best layman's explanation is that when you record bits on magnetic media and
then read them back, the timing between bits is not the same when read as it
was when written. The variances are dependent on the distance between bits, and
on the density of the bits at any given time, both of which are a function of
the actual patterns written on the media.  Precompensation adjusts the timing
of the bits as written in order to offset the changes in timing that will occur
on reading.

-larry

--
It is not possible to both understand and appreciate Intel CPUs.
    -D.Wolfskill
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|   //   Larry Phillips                                                 |
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