Info on UM8397 floppy disk IC?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Dec 26 17:42:58 2003

>
> > Quoting from the notes in that zip file:
> >
> > "Note that most PC floppy controllers have broken single density modes.
>
> Well, that's old hat to me. Around 1988 or so, I suddenly got problems
> reading "elderly" 5.25" discs on new PC's. The reason was, that the 160K and
> 320K capacities were "designed out" of the floppy controllers normally used
> in PC's

Since when have the MS-DOS 160K and 320K formats been 'single density'???
To me, single density disks use FM encoding, and the original IBM PC and
PC/XT controllers are strictly double-density (MFM) only devices (I have
read the schematics...)

Any PC floppy controller that can do the 360K format can also handle 160K,
180K, and 320K _in the hardware_. They're all much the same thing (and
are all MFM) . Of course your OS may not support such formats.

But very few PC floppy controllers (particularly single-chip ones)
correctly handle single-density (FM) operation.

-tony
Received on Fri Dec 26 2003 - 17:42:58 GMT