Re: Latest mac that supported 800k ProDos disks

[dempson@actrix.gen.nz (David Empson)]

Sean Fahey <a2fan@hotmail.com> wrote:

> On Monday, September 3, 2012 11:43:11 PM UTC-5, Sean Fahey wrote:
> 
> > Isn't the PCT disk controller pretty much the same SWIM as on the
> > Mustang controller (Superdrive) with a little extra logic?
> 
> >>>>
> 
> I'm sorry - I meant to say it's predecessor.

Yes, its predecessor, basically an early revision of the SWIM before
Apple was ready to use it themselves.

The PCT implementation doesn't support high density, but does support
720k on double density disks. We're just not sure _how_ it doesn't that
with an 800k Apple drive, as nothing else using the SWIM is able to pull
that trick.

Best theories are extra hardware support to disable the variable
rotation, or the bit clock is tweaked (perhaps via a DPLL) to
compenstate for the variable rotation.

-- 
David Empson
dempson@actrix.gen.nz