13 Apr
2004
13 Apr
'04
6:50 a.m.
On Mon, 12 Apr 2004, John Allain wrote:
Nice. Looking up SYS.COM in the Ref (v3.3) manual:
"DOS statrup requires {(sic)IBMBIO.COM and IBMDOS.COM}
to occupy the first two directory entries, and because
IBMBIO.COM must start at the beginning of the data area of
the disk." that explains a lot.
MSDOS PCDOS
machine-specific IO code IO.SYS IBMBIO.COM
Microsoft-provided OS code MSDOS.SYS IBMDOS.COM
But, format/b documentation confusingly mentions
that the floppy is also formattted 8 sectors per track.
Sounds almost wrong -- the capacity doesn't change
for example.
Probably vestigial from very early machines that could not boot
360K diskettes, only 320K?
5" diskettes went to 9 sectors/track some time after the
machine's release, I forget the PCDOS version. The 8spt was
a very conservative choice, in fact a little odd, as the
9th sector always fit. There were four diskette flavors,
single and double sided, 8 and 9 sectors/track. Clearly only
double-sided/9spt survived.
(My personal MSDOS 3.x machine was a multibuss box with 8"
drives that took all the standard permutations but also a
1024 byte 9 sector format that gave me a LOT of storage,
nearly 1.5Mbytes/diskette. Wowee zowee.)