Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hp-pcd!hpvcfs1!johne
From: johne@hpvcfs1.HP.COM (John Eaton)
Newsgroups: comp.periphs
Subject: Re: What is "Write Precompensation" on hard disks
Message-ID: <930001@hpvcfs1.HP.COM>
Date: 18 Apr 89 15:44:57 GMT
References: <1574@ccnysci.UUCP>
Organization: Hewlett Packard, Vancouver, WA
Lines: 14

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< What is write precompensation? is it some sort of offset used when seeking?
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Very simple. Magnetic media systems will distort the signal so that you don't
always get back what you put in. If you store a pattern with a narrow pulse
of flux in one direction in between two wide pulses of the opposite polarity
then the narrow pulse will tend to shrink when it is read. Since this is 
predictable you can prevent it by writing a much larger pulse than you really
want because you know it will shrink down to the proper size when read.


John Eaton
!hpvcfs1!johne