[rescue] Re: Current collections...

Ron Wickersham rjw at alembic.com
Tue Apr 6 20:04:11 CDT 2004

Geoffrey S. Mendelson wrote:
> Dave McGuire wrote:
> >    No...sampling != demodulation.


> There really is not a lot of data on them, AFIK Comodore (PET, VIC-20, C64)
> wrote data at 300 bits per second as did the 8 bit Atari's. Some CPM systems
> went as fast as the 1200 bits per second. I think that the IBM PC used 1200
> bits per second, but I've never seen a tape for one.
> What I don't know is the baud rate and encoding method, but I'm sure it's
> well documented.

PETs don't modulate the tape on audio...just DC current reversals thru the
head and a simple slicer for playback.  you can't copy Commodore tapes on
standard audio recorders.   (on the other hand they are very robust and
you can playback tapes that have been crinkled or otherwise abused).  the
tape units look like standard cassette mechanisms but have the special
electronics board inside and a pc board edge connector on the end of the
cable to plug them into the computer.  you had to push the mechanical play
button on the deck but the motor was started and stopped from the computer.


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