Re: HD floppy on a IIgs?

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

mojoehand <mojoehand@gmail.com> wrote:

> On Jun 1, 10:53 am, Warren Ernst <wer...@gmail.com> wrote:
> > On May 31, 11:20 pm, mojoehand <mojoeh...@gmail.com> wrote:
> >
> > > I know that you need a special interface card to support a 1.44 MB
> > > floppy drive on a IIe. Assuming I had a compatible drive, does the
> > > IIgs Smartport support HD drives?
> >
> > > In other words, can I take a HD drive from a vintage Mac and use it on
> > > the IIgs? Can I format, read and write HD floppys with it? If so, is
> > > it possible to read/write MSDOS disks?
> >
> > Just to be thorough, if you take a 1.44MB High Density 3.5" floppy
> > drive from a suitably old Macintosh and plug it into the GS SmartPort,
> > the drive will act like a normal 800KB floppy drive. It's the magic of
> > the "SuperDrive Controller Card" that makes it read and write 1.44MB
> > floppies.
> >
> > You should also note that Apple used two different types of HD floppy
> > drives on old Macs, and it is the older ones that are shared with the
> > Apple II. Basically, if the drive came from a 68K Mac, it should be
> > good to use. If it came from a PowerPC-era Mac, then it is not only
> > less likely to work properly with ProDOS disks, but you can't just
> > pull the mechanism and expect it to work with an Apple II.
> 
> Thanks to all for the input. I suspected that it wouldn't get me
> anywhere, but I wanted to make sure.
> 
> Pie in the sky question - Is it possible to write a IIgs driver that
> would make the Smartport work with the 1.44 MB drive?

No. The IWM controller chip can't transfer data fast enough (nor can it
handle MFM-encoded data). In addition, a 1 MHz 6502 or 65C02 isn't fast
enough to keep up with the data stream.

The SuperDrive controller achieves the feat by using a SWIM chip instead
of an IWM, and has its own CPU (a 2 MHz 65C02) and RAM for buffering.

-- 
David Empson
dempson@actrix.gen.nz