Hi, I would like to forward a question by harka@xxxxxxxxxx:
Can FreeDOS handle floppies of special sizes bigger than 1.44 MB,
for example 1.72 MB? I seem to remember that when I format
(fdformat / SuperFormat) floppies to big size using Linux, neither
Windows nor Dos were able to use them. Of course I did use a Dos
filesystem, but still... Vgacopy for Dos can "high format" as well
and has a driver to make Dos more compatible with those special
sizes, but I was told it would not work. Please mail if you know
working drivers and high-size formatting tools for FreeDOS...
To specify what LBAcache would do with those: LBAcache can handle
all floppy formats with 2 heads and 18 sectors per head/cyl, but
according to my /etc/fdrpm:
720k uses 9 sectors per track (cyl), 5.25 inch formats use 9, for
1200k 15, sectors per track, and 1680k uses 21 sectors per track,
so none of those is compatible with LBAcache. Taking into account
other formats found in /usr/src/linux-*/drivers/block/floppy.c:
2.88 MB uses 36, 3.12 MB 39 (need special drives) sec/track.
1.48 MB 5.25 inch is compatible, as is 1.49 MB 5.25 inch. There
are really a big number of other, incompatible formats, and even
for the "compatible" formats mentioned above, you cannot be sure.
If you have an idea how to efficiently detect the number of heads
used (2 except for 360k and smaller) and especially the number of
sectors per track, preferrably independend of the filesystem type,
AND think that supporting sizes other than 1.44 MB for LBAcache
floppy caching, please tell me. The only way I can think of would
be reading the geometry information in the DOS boot sector, but
this obviously only works for the DOS filesystem. And I would
probably need a buffer to read the bootsector to - or does DOS
never write to a disk before reading the bootsector? Then I could
use the buffer provided for the first read from each new floppy to
read the bootsector, analyze it, and after that, do the read that
was actually supposed to happen. I do not really like the idea, but
if you consider it to be useful, tell me. I might add an "analyze
boot sector on floppy change to allow for other sizes than 1.44 MB"
command line option.
Another request for those that prefer having a risky live:
Single sector access to floppies with less than 18 sectors per
track can work. Do not ask me how to avoid multisector acces wrapping
around track boundaries (using an old kernel could work? Or configure
the multisector stuff to be off, preferably only for floppy access!?
Maybe Bart or Tom can comment on this). For NOW, lbacache only checks
for the BIOS (int 13.1500) disk type to be less than or equal to 18
sectors per track and less than or equal to 2 heads. This part of
setup.asm is DANGEROUS if you do multisector access. However, in this
version other sizes than 1.44 MB are not yet automatically blocked!
So maybe you can play with it a bit. Careful, you may trash your floppy
and data copied to/from the floppy will be broken under the conditions
hinted above. Tell me if I should make setup.asm more PICKY to allow
ONLY 2 head / 18 sectors per track drives to be cached. Be warned that
this may still let using smaller disks in a 1.44 MB -drive- slip through!
Very technical mail, but maybe I get some interesting feedback on this
one. Thank you and take care, do not risk important data!
Eric
PS: BONUS question: If you can run descent for Dos (shareware version)
with FreeDOS, please tell me which kernel you are using! It is possible
that either kernel 2027 or the xmsswap (otherwise great!) feature of
FreeCOM command.com broke it for me, so I would be interested which
versions do or do not run Descent. I get a segfault right at the start,
with or without -Verbose -NoNetwork options.
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