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Reading Mac 800 Kb format FD's on PC



Without trying to give a lecture, perhaps some of you would like to know
*why* a PC diskette drive cannot read MAC 800 Kb. floppies. When Steve
Wozniak was still Apple's engineering guru he had a bright idea for a scheme
that enabled him to store 800 Kb on a diskette where PC's only could store
720 Kb. As with his Apple II design where floppy access was a real miracle;
fast, cheap and reliable and mostly done in software (!) his idea showed
true genius.

His idea was to have a variable speed of the floppy drive's motor. When the
head moves to the outer (wider) track the motor spins slower. This means
that the amount of information on those tracks is larger. This scheme can be
compared to that of CD's.
Wozniak is still honored with the fact that the floppy controller in a Mac
is still code-named SWIM (Steve Wozniak's Integrated Machine).

The disadvantage was that Apple needed special floppy drives to read this
format. When Mac's still had huge costprices nobody cared about that, but
nowadays Apple has published an idea that in the future they will skip using
these drives. From that moment on even Mac's cannot read 400 and 800 Kb.
diskettes anymore. I guess Apple will then supply an external SCSI 400/800
Kb. drive as an option.

So, to my knowledge it is really impossible to read 400/800 Kb. floppies on
a PC without any special hardware. The normal floppy disk controller in a PC
(upD786 or comaptible) simply cannot perform the required function.


Ernst J. Oud

Contrary to modern belief; in The Netherlands we do not wear wooden shoes!