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Re: Hardware musings

mdj wrote:

Michael J. Mahon wrote:



Then there's all those out there who would enjoy the convenience of
adding an Apple 5.25" drive to their PC's to make imaging all the stuff
that's available now simpler.


What do you mean by "imaging all the stuff that's available now"?

Do you mean reading real disks and imaging them (which involves the
complexities we are discussing) or writing real disks from the images
available now (which is quite different, since they are almost all
"normal" images).



Sorry, I meant to say, writing disks from available images. While
there's a dozen ways of doing it, they all 'seem' quite complex
compared to just plugging a Disk II into a PC


I agree that it would be very desirable to be able to convert a
"universal image" into a physical copy-protected disk.  Methods
for doing this should be considered as the universal image format
is defined.

Unfortunately, I don't think it's an easy problem to take image
data for all quarter tracks, together with sync info and soft bit
info, and turn it back into a physical disk that, when imaged,
would create the same file that produced it.

A relatively simple problem is that to control automatically even
the approximate track length in bits requires writing with a variable
clock (quite doable with a microcontroller).

Part of the problem is that data read from a "track overlap" region
will be an artifact of the micro-variations in rotation speed of the
drive on which it was written, and there is no way to control that
on the writing drive (floppy drives don't have a way to read adjacent
data as new data is being written).

What's needed, again, is better knowledge of what data read from
the disk is actually *relevant* to the program's copy protection
scheme.

One can envision algorithmically "observing" the execution of a
program as it is used (perhaps extensively), and creating lists
of relevant disk "features" that must be present, but even that
involves human interaction.

-michael

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