Floppy drive pin 2 question?

Steven Canning cannings at earthlink.net
Thu Mar 10 19:18:47 CST 2005


I proposed doing exactly that (i.e. passing "raw" floppy data through a
parallel port) last year along with some simple math that showed it could be
done. The concept was "poo-poo'd" by some, but in the real world it has been
done already to image the following; Amiga (".ADF"), Apple disk ][ (".DO"),
Atari ST (".ST"). Commodore 1541 (".D64"), PC (".IMG") and
single-density (".DSK"). The URL for the write-up and software is;

Very cool! Best regards, Steven C.

> On Thu, 2005-03-10 at 16:29 -0600, Randy McLaughlin wrote:
> > I have a webpage describing disks and disk drives.
> Yep - most useful it is too! :-)
> > Pin 2 on a 34 pin floppy connector is a little used pin.  It was used to
> > change the RPM on some 5.25" 1.2mb drives.
> >
> > It changed the RPM from 360 RPM (pin 2 high) to 300 RPM (pin 2 low).
> > was supposed to make it easier to read/write DD disks in a HD drive.
> >
> > Only early AT controllers needed it, later controllers kept this pin
> > and used an odd transfer rate.
> Interesting. I'd always assumed that 1.2MB drives always changed the
> speed too.
> I was pondering earlier how much memory it'd take to buffer a whole raw
> track of data; presumably the maximum would be a 1Mbps rate at 300rpm
> rotation? (and say sample at 16x, plus store some form of clock info. It
> still doesn't work out that bad).
> I'm sure it must be possible to build some gadget that'll hang off a PC
> parallel port and buffer data to local (static) RAM, allowing slower-
> speed transfer to/from the host machine. Hopefully without needing
> microprocessor control (i.e. bunch of RAM, few counters or something :-)
> Maybe there's some reason it can't be done - otherwise I'd expect
> someone would have done so by now! :-)
> cheers
> Jules

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