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From: "RetroMIDI" <fox AT zip DOT com DOT au>
Newsgroups: comp.os.msdos.programmer,comp.os.msdos.djgpp
Subject: Re: Creating a copy protected floppy
Date: 13 Jul 2005 18:30:13 -0700
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I once made some money writing a copy-protection program to ude under
QBASIC.

It is possible to write EXTRA sectors on a particular track so that the
sector numbers are within the data sections of lower numbered sectors.

If you diskcopy the disk then the inbetwen sectors are not there and
can not be read becaue they do not exist.

To foil a TSR that pretends there are sectors there, you write data to,
say, sector one of the messed track and then read the same data back,
but addressing it by its other description as sector 9 (for example)
and at a specific offset.

These reads and writes are all absolute into a part of the floppy that
you mark as damaged or as a hidden, system file so that it does not get
erased in error.

This is difficult to, but works, because the floppy can only be copied
by a professional duplicator which ignores the FAT table and just
duplicates the disk bit by bit irrespective of the nature of the data
or the density or sector architecture