Problems reading older disk on newer drive

[Tom Jennings]

On Sun, 19 Dec 2004, Nico de Jong wrote:

> Normally, there would not be a problem, supposing it is a 360K disk (I guess
> you are talking about 5.25" disks).
> What I _have_ seen, is that "modern" BIOS'es have problems / cannot read
> disks formatted as 320K. Back in the old days, 5.25" disks came in even more
> flavours, like 160K (I've never seen an 80K 5.25" though)

Somewhere I have a list of the FATid byte values for all the
IBM and MSDOS 5.25" diskettes. Basically they include:

	sides	density	spt	capacity
	1	double	8	160k
	1	double	9	180k
	2	double	8	320k
	2	double	9	360k

spt means 'sectors per track' physical

Then there's issues with @#$%^ IBM (or m'soft) looking for
text in the boot sector and not just that FATid (the 1st byte
of each FAT) to ID disks, rendering otherwise-proper MSDOS
diskettes unusable.

AFAIK, IBM never supported single-density. The hardware isn't
the problem, there's no FATid defined for it. And who wants
86K diskettes, anyways?