Reading various format 5.25" floppies on a PC

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Mon Jun 16 19:09:01 2003

--- "Fred Cisin (XenoSoft)" <cisin_at_xenosoft.com> wrote:
> On Mon, 16 Jun 2003, Tony Duell wrote:
> > Depends on the PC and the Mac :-).
>
> It sure does. Comparing NEW PCs with OLD Macs is ludicrous.

Indeed - and it cuts both ways ;-)

> And it also is an issue of how competent the individual is. I do NOT
> have the skill to solder surface mount, nor to figure out how to modify
> the disk operations of the Mac.

Those are two different skills. Soldering surface mount is a matter
of vision, manual dexterity and practice. The correct tools help, but
I can prove that you can do a lot with just a temp-controlled iron
and a steady hand.

Modifying the Mac disk controller is an entirely different kettle of
fish - like the Amiga, unlike old ISA PCs, it's a custom affair. The
oldest Macs use the "IWM" chip the Integrated Woz Machine. Single-
sided Mac drives varied the drive speed to achieve several recording
densities; later ones varied the bit clock under software control
(similar to what the Commodore 2040/3040/1541/2031/etc. drives did).
Between that and GCR vs MFM, there are major obstacles for getting
different platforms to read each other's disks. The one that is the
most universal is the Amiga - it uses part of the sound chip for a
4096-bit shift register to clock an entire track in or out. The
hardware handles flux reversals - the *software* cobbles up the
MFM formatting, intersector gap, headers, data and all. In practice,
the graphics chips perform the binary<->MFM translation, but that's
just because it can - it's doable purely in software, albeit more
slowly. The biggest problem with Amiga FDC design is that it's limited
to DD data rates - its high-density floppies spin at 50% and are
somewhat scarce (AFAIK, the drive itself senses the HD hole and spins
the disc at the right rate; it's not a software thing).

Unless you start from scratch, I doubt there's any one platform that
has a chance of reading "all" floppy formats - that's why they made
the Catweasel. It's a shame that the software never lived up to the
promise of the hardware.

-ethan
Received on Mon Jun 16 2003 - 19:09:01 BST