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From: John Ames <commodorejohn@gmail.com>
Newsgroups: comp.os.linux.misc,alt.usage.english,alt.english.usage
Subject: Re: Floppies
Date: Tue, 16 Sep 2025 13:34:11 -0700
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On Tue, 16 Sep 2025 20:28:35 +0200
Bertel Lund Hansen <rundtosset@lundhansen.dk> wrote:

> > On the PC the format was handled in software (BIOS or even
> > userland), =20
>=20
> The 3=BD" floppies could hold 720 kByte when used on a PC. If you set
> up config.sys correctly, it could handle 144 kByte.
>=20
> I haven't tried other formats on a PC, but I would be surprised if it=20
> could handle other formats - without formatting.

The standard PC boot sector contains disk geometry info which can
*theoretically* represent a wide range of disk formats; I'm not sure
how far that can practically be pushed. The MS-DOS FORMAT utility
supported a lot more options for disk sizes, but I don't know if it
could read any arbitrary geometry as specified in the boot sector.

The controller itself imposed some limitations as well (at least some
of the parameters were shared across both drives on the ribbon, which
made for interesting times if one was trying to access a non-standard
format while running off a floppy in a standard format!) And only FM/
MFM encoding was supported, which meant that GCR-format disks (Apple
II, 400/800KB Mac, most Commodore) couldn't be accessed in any case.