Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!cs.utexas.edu!rice!uw-beaver!sumax!thebes!happym!polari!tm
From: tm@polari.UUCP (Toshi Morita)
Newsgroups: comp.sys.apple2
Subject: Spriral-tracking
Keywords: copy protection
Message-ID: <1544@polari.UUCP>
Date: 12 Apr 90 10:50:16 GMT
Distribution: na
Organization: Seattle Online Public Unix (206) 328-4944
Lines: 21



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toddpw@tybalt.caltech.edu (Todd P. Whitesel) writes:

>But it is for that reason that data is never stored closer than 3/4 of a track
>apart, and since 1/4 tracks are a pain to work with (you have to do gross
>things with the stepper magnets) DOS only uses full tracks to store data.
>Spiral tracking copy protection schemes use quarter tracks but spiral it
>such that data is never closer than 3/4 track at any point on the disk
>(assuming they are reading real data and not checking for the presence of
>intentional errors).

If I remember correctly, Br0derbund's spiral tracking (a la Choplifter) used 
adjacent half-tracks in concentric half-circles to achieve one of the most
difficult copy-protechtion schemes ever, (not quarter tracks).

Nice to see all the slick programmers (kadickey, nicholas) on Usenet!

Toshi Morita
..!uunet!microsoft!uw-beaver!sumax!polari!tm