On 2 Oct 1998, Eric Smith wrote:
> I'm not sure that would work for the protection schemes that actually
> wrote the sectors while the stepper was in motion. However, fortunately
> that technique wasn't very common since the mechanical characteristics
> of the stepper et al tended to vary somewhat from drive to drive.
Ah! I always assumed "spiral tracks" were simply quarter tracks written
every step of the stepper arm, and not while the stepper arm was moving.
In fact, I don't know how you could write bytes to the disk while the arm
was moving since the step had to be controlled by the program. Its been a
while since I messed with that level of detail on the disk drive but was
there any time to actually write bytes while the arm was being stepped? I
thought you simply poked the right locations and the head moved instantly
to the next step, no waiting required? Come to think of it, I believe
there was some pausing involved.
> The other copy protection problem that simple attempts at raw copying won't
> solve is where the software expects arbitrary features of arbitrary tracks
> to be time-synchronized. It's easy to build hardware that synchronizes
> the index pulse (which the Apple doesn't even use), but that's not actually
> sufficient.
Yep, synchronized tracks. Wizardry used this technique and it was one of
the most impossible disks to copy. I remember only ever being able to
make one bit-copy of it that worked.
Sam Alternate e-mail: dastar_at_siconic.com
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Received on Fri Oct 02 1998 - 05:04:16 BST