8-inch disk drives

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed Jul 23 22:35:46 2003

> There seems to be a lot of discussions regarding handling old / odd
> floppy disk formats. What Fred said above is a truth with severe
> limitations. It is my experience, that modern floppy controllers, and
> _especially_ those embedded on motherboards, will
> not read anything other then 3.5" disks (720K, 1.44M and 2.88M) and
> 5.25" (360K, 1.2M).
>
> The older formats, like 5.25" 320K, not to speak of 160K are not

I am wonderign how on earth you can make a disk controller (note, not the
OS driver software, the physocal controller) that works correctly with a
9-sector-per-track format, but fails with the 8 sector-per-track version,
all other parameters being the same. Because that's the only difference
between the 320K and 360K MS-DOS formats.

Similarly, I can't understand how you can make a controller that works
correcty with a DS disk but fails with the SS version.

> supported, or should I say are not supported on the systems I've
> delivered for the last 8-10 years.
> Please note that I only take MS-DOs formats in consideration. Anything
> other, like CP/M or 8" disks, is totally out.

Err, considering that the 8" drive and the 1.2M 5.25" drive are very
similar at the hardware interface level, it would be difficult to make a
contorller that worked with one but which fails with the other.

And some CP/M formats are pnysically almost identical to the standard
320K MS-DOS format. Hardware that can read one can also read the other.

>
> There was a mention of MicroSolutions UniForm software. The software
> (at least the version I had) was able to read (some) CP/M formats by
> doing nasty things to the parameters in the floppy controller. When I
> tried it again some years ago, it was a total flop, probably because of
> the limitations as described above.

The main problem is that many PC disk controllers (going back to the
original IBM card in the PC and PC/XT -- check the schematics) can't
handle single density (FM) recording correctly.

> scrapheap just for this purpose. Or maybe even a museum piece: the IBM
> AT. In other words : the older the better.

I happen to be typing this on a much-hacked PC/AT (orignal IBM, original
motherboard with my own hardware mods, etc). Still works fine, and I have
no intention of downgrading to a more modern machine.

-tony
Received on Wed Jul 23 2003 - 22:35:46 BST