Polymorphic System88 disk

[dwight elvey]

> From: cclist at sydex.com
>
>> Date: Tue, 8 Apr 2008 05:59:37 -0700
>> From: dwight elvey
>
> Will all respect for your efforts, Dwight, at least you knew the
> origin of the diskette and had a faint idea of what might be on them.
>
> You haven't lived until someone shoots you a bunch of diskettes with
> everything being unknown--the modulation technique, the code
> representation, the data rate or track spacing or byte width, much
> less the file system.
>
> Your Polymorphics floppies sound a lot like a bunch of diskettes I
> got in recently from a manufacturer's in-house PCB stuffing robot.
> The format appears to be a "roll your own".
>
> It's hard to say which is the most fun--diskettes discovered to be
> GCR where you have no idea of what the group size is, nor what the
> groups correspond to. Or diskettes written on something like a
> typewriter where the code's not ASCII, nor does A immediately precede
> B--and you have nothing that says "this is a printout of what's on
> the diskette".
>
> Hint: You start with a statistical analysis of the pulse stream and
> go from there.
>
> For me, it's a lot of fun, ferreting out things by bits and pieces
> until the big picture emerges.
>
Hi Chuck
 I was lucky. I even know what the directory structure looks like.
I did have to fix my scope. Several of the delayed sweep setting
were not working correctly. It turned out to be a 4000 series analog
mux used to select the delay capacitors.
 Still, I think this is one case that I'd liked to have a nice digital
scope for. As a general rule, I prefer the analog scope but there
are times it is hard to be effective with. Having a single sweep
stay on the screen would have allowed more in depth analysis
of the bit streams.
 I did enjoy the hunt but as Eric says, if someone wanted to pay
for it, it would have been expenssive.
 What surprised me the most was the complete change of header
and track usage. I'll never know what made them change it so.
 I do admit the 00,ff at the end of the data makes sense. I wish
they'd used the same for their tape format. It would have sped
up the recovery of tape data that I worked on a few years back.
 Now comes the work of actually transfering the images. I have to
run at 9600 baud. I estimate about 8 minutes per disk. I've got
some 50 disk.
Dwight

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