Re: Is it possible...

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

Bryan Parkoff <nospam@nospam.com> wrote:

> "David Wilson" <mcs6502@gmail.com> wrote in message 
> 1150366859.998137.226360@u72g2000cwu.googlegroups.com">news:1150366859.998137.226360@u72g2000cwu.googlegroups.com...
> > Frank Werner wrote:
> >> ...to write on a 3,5 Inch Floppy with a PC that an Apple can read?
> >
> > Yes but...
> >
> > I do it all the time but my IIgs has a Superdrive card and an Apple
> > 1.44MB 3.5" drive. I use Ciderpress on a PC to create a 1.44MB ProDOS
> > disk.
> >
> > If you only have 800KB 3.5" drives on your Apple II then you are out of
> > luck at present.
> >
> > I think a neat circuit would be a microcontroller with a USB interface
> > driving a 3.5" drive in such a way that it can read/write/format 800KB
> > GCR diskettes. If it reports itself as a USB mass storage class device
> > then any USB aware PC operating system (Windows XP, Linux etc) would be
> > able to read and write Apple II diskettes.
> 
>     So USB is not invented yet to work with GCR drives?

Apple stopped using GCR as its main 3.5" disk format on the Mac in 1988,
and on the Apple II in 1992 (end of the IIgs and probably the IIc+) or
1993 (end of the IIe and all other Apple II products). They completely
eliminated built-in floppy drives in 1998 when USB was introduced on the
Mac.

Mass market USB floppy drives are designed to support MFM disks
(720K/1440K), which is the standard format on MS-DOS/Windows/Linux. It
has also been the standard format on the Mac since 1988 (just with a
different file system).

In 1998, designing a mass market drive to support a ten year old disk
format (which is rather complex to implement) didn't make a lot of
sense, especially when you could just use an old Mac to convert any old
disks into newer formats (ignoring protection issues). I don't think the
million or so Apple IIs with 3.5" drives sold as recently as 1993 would
have been an influencing factor.

As time goes on, it makes even less sense to design such a product as
the potential market will be dwindling further.

To summarise: there is no mass market for USB drives which can access
GCR formatted disks, so any such drive would be a niche product (very
expensive) or have to be made by a hobbyist.

There are some technical problems which would need to be solved. The
main one is that on Apple's 3.5" GCR disks (400K/800K) the drive
rotation speed is supposed to vary depending on the track being accessed
(in five speed bands, 16 tracks per band). Modern cheap 3.5" drive
mechanisms have fixed rotation speed, so it would be necessary to
simulate the variable rotation speed by adjusting the timing of the bit
cells, probably requiring a rather fancy timing circuit with adjustable
clock frequency.

A better hobbyist solution would be to build a drive with a USB
microcontroller, SWIM or IWM, and a genuine Sony SuperDrive or 800K
drive mechanism.

There are a few problems going down the SWIM/SuperDrive route, due to
lack of publically available documentation.

The IWM/800K combination has much better documentation, though still
nowhere near as complete as for Apple II 5.25" drives.

-- 
David Empson
dempson@actrix.gen.nz