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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Hard Drive Zapping
References: <firstname.lastname@example.org> <3D743FF8.69A16568@webaccess.net> <email@example.com>
Date: Tue, 03 Sep 2002 14:49:14 GMT
NNTP-Posting-Date: Tue, 03 Sep 2002 07:49:14 PDT
> > The trouble comes about because servo uses a very robust
> > sync and since servo data is written so that it is radially
> > coherent, the servo sync can be found off track.
> Perhaps a dumb question. Is the servo data distributed around the
> circumference of the platers? One a single platter (ie top or bottom)?
In most drives, the servo information is interspersed in the data. This
forms what are called servo sectors in that the servo data is in nearly
radial stripes from the edge to the center of the disk. The controller
in the drive puts user data between servo sectors. In modern drives,
because of zoned bit recording (nearly constant density) the data
sectors do not bear a simple relationship to the servo sectors. The
drives I have worked on had two sorts of data encoded in the servo
sectors. A track number and sector number identifier grey coded to be
less ambiguous and analog position pulses which are peak detected (not
sure who uses this these days) or area detected (DEC used this and later
WD). The analog information is used for fine tracking while the digital
information is used for fast motions in which the head may move 100's of
tracks between servo sectors. There are all kinds of variations on this.
Basically all the manufactures do it a bit differently (there is no
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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