25 Jul
2021
25 Jul
'21
12:14 p.m.
> My recollection of the DMF Microsoft period was
that if you purchased a
> retail MS product using the DMF format and couldn't get it read on your
> system, a call to MS would result in a standard format copy being shipped.
On Sun, 25 Jul 2021, Grant Taylor via cctalk wrote:
It's my understanding that The DMF disks that
Microsoft (and comparable from
IBM with PC-DOS) used a different non-FAT file system which took up less
space on the disk, thus yielding more storage for data. But that they both
fit on the same /standard/ ""1.44 MB disks.
I also seem to recall that Macintosh's could get 1.7 MB on the same ""1.44
MB
disks.
But I could be completely wrong.
Using a more efficient file directory system isn't a bad idea. But, it
won't gain enough additional, just one or two tracks.
But, no, that's not what they did.
The Microsoft DMF is a normal FAT system! They just cheated on the
"standards" for the intersector gaps to get 21 sectors per track, instead
of the "normal" 18 sectors per track.
MOST?, probably not ALL, of the Macintosh 1.4M hardware is similar enough
that, with the right software ("drivers"), it can do the same, and
read/write the Microsoft DMF format.
The IBM XDF format is weirder. It is based primarily on mixing different
sector sizes on the same track. Although read and write are not an
issue, It is "impossible" to FORMAT disks that way with the NEC 765
type FDC on the PC, but there are ways to cheat and fool it into doing it.
I don't know whether the Macintosh disk controllers can handle it.
Neither the DMF nor the XDF can be read or written with virtually any USB
drive, or many other special drives, such as Floptical or LS100, because
those drives have firmware that is locked in to the "normal" format.
--
Grumpy Ol' Fred cisin at xenosoft.com