stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5 1/4 floppies)

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Apr 7 23:54:31 1999

The disk drive has a place beyond which its head assembly won't move. If
you've ever written FDC code, you know what it sounds like when you try to
go beyond the limit. What's more, there's a sensor to tell you when you're
at that point, though I doubt Apple used it. It's just as easy to move the
heads until you're sure they've gone as far as they can. Once you've done
that, what better way could there be than to look for a track and then
adjust until the signal is readable? That's how drives of all sorts work
today. Of course, they all have some way of establishing where a track
ought to be to begin with.

Dick


-----Original Message-----
From: Max Eskin <max82_at_surfree.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Wednesday, April 07, 1999 8:53 PM
Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5
1/4 floppies)


>On 8 Apr 1999, Eric Smith wrote:
>>> These fellows
>>> spent a couple of sessions talking about and demonstrating the screwy
means
>>> by which certain game vendors in the Apple market were "protecting"
their
>>> wares by altering the timing of the positioning routine, thereby making
it
>>> possible to write tracks "off the track" by changing the time delay
between
>>> a known cylinder position and the point at which the specific track was
to
>>> be written. This made it impossible for someone using the stock timing
of
>>> the positioning mechanism to read the diskettes so written.
>
>How does this work? Do you mean that the disk drive has no internal means
>of judging whether or not it's on the right track and that this is
>determined by the contents of the disk?
>
> --Max Eskin (max82_at_surfree.com)
>
Received on Wed Apr 07 1999 - 23:54:31 BST