Re: [Vaporware alert!] Portable Apple II Clone Concept

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

Michael J. Mahon wrote:

> Designing a virtual Disk ][ that handles protection schemes just like
> a real one would be quite a challenge--as would the data representation
> of the image to load it up and the reading scheme to recover the exact
> format of the protected disk in the first place!

I agree that an optimal representation would be quite tricky, however I
believe that a naive data model, which simply captures the bitstream or
fluxstream, that passes under the read head, plus a table/index of what
particular head positions these data streams exist at would be
sufficient. If its resolution is sufficiently high as to match or
exceed the maximum read rate of the Disk II/Apple II combination, then
theoretically any disk that's readable can be represented.

Of course, the 'tracks' of data would need to be represented
synchronised, and 'played' back as such.

The only holes I can see with such an appoach is the volume of data
created in such a process, and it may be impossible to capture it at
such a rate on an Apple II

The data should however be readily compressible using a simple
technique.

To me, the logical data representation is the easy part. Implementing
it in a useable way is the challenge.

It would be really nice if somebody would come up with an interface for
a PC that can control a Disk II. It should be reasonably easy to
connect direct to the drive and reconstruct the IWM in software, and a
PC parallel port probably has enough I/O pins to handle the job.

To be really hardcore, you could bypass the drive electronics and
sample the read/write head with an ADC, capture a couple of seconds of
data per possible disk head position, and use a software analysis to
process the data. Using this approach, you could determine the exact
data stream from the flux transitions, and the exact locations of
'real' tracks by comparing adjacent head position samples, which should
show the same signal at lower strength, then be replaced by a new
signal as you approach the next 'real' track. It'd be possible with
this scheme to replicate any Apple II disk, regardless of how it'd been
protected.

Unfortunately I think the hardcore approach would be used by so few
individuals that it wouldn't capture enough disk images to justify the
effort of constructing it.

A simple to build/cheap to buy interface however, that integrated into
an emulator such that Copy II+ could be used to image the titles, might
get enough attention to make it worth the effort.