Re: Hardware musings

["mdj" <mdj.mdj@gmail.com>]

Michael J. Mahon wrote:

> In principle, but I'm not aware of any complete "catalog" of the
> methods used, and often the same title was protected in different
> ways in different "printings".

Well, the Copy II Plus database is a good start, and would cover the
majority of titles.

> The problem is that only human intelligence can determine which way
> a particular disk is *actually* used.
>
> If you want to save a minimal amount of data, then you'll have to
> manually determine--through extensive testing, since a failed copy
> may not show up until later in a game--exactly what needs to be on
> the disk (or image) to satisfy the program.
>
> The only practical way to avoid this hard work is to save everything
> that could *possibly* be used by a program, and that takes considerably
> more space and time (to create).
>
> If you want a "general purpose" tool, then I think the latter approach
> is the only one that will work.  As I've said, I think that involves
> saving every nibble readable on every quarter-track, together with
> lists of all the "soft" bits on those tracks.

I agree in terms of creating the images, unfortunately you couldn't
transfer that data successfully back to a disk without knowing which
track positions were actually written, as writing to each quarter track
would trash its neighbours.

I suppose though, that the method would suffice for preservations sake,
and Copy II Plus data can be used to eliminate known spurious data for
the majority of titles. The rest could be done 'by hand' by those who
have the determination to do so.

The only automatic way I can see of getting around this would involve
sampling the read head directly in analog, and compare the signal
amplitude of adjacent tracks, but this would involve a hardware hack to
the drive and much more sophisticated software.

Matt