25 Jul
2010
25 Jul
'10
11:19 a.m.
[USB floppy controllers]
OK...
Wel, there's this PC for a start. It's a much-hacked PC/AT (8MHz version)
using the origianl motherboard and many of the original expansion cards.
The main changes are a 486 kldugeboard in the 286 socket (so I can run
linux), an earle IDE controller linked to a now-ancient drive, a 1.44M
3.5" floppy (as well as the origianl 1.2M one of course), a patch to the
ROM BIOS to modify the drive parameter tables (2 extra EPROMs and some
address deocnding logic fitted ot the mainboard, kludgewires all over
theplace), and various other piggy-back chip mods to correct timing
problems, add a drive-in-use LED, and so on.
Other 80x86 machines I own include IBM PCs, PC/XTs, a PC/XT286 and a
PCjr. A couple of other clones I think, then a DEC Rainbow, RM Nimbus,
HP150, HP150-II, HP110, HP Portable+, HP95LX , 100LX and Omnigo 100, a
Sirus (Victo 9000) and doubtless others that I've forgotten about.
-tony
But I suspect
they can't do FM (single density) either. Can they handle
250kbps (360K, 720K) or 300kbps (360k disks in a 1.2M dribe basically)
data rates? Or do they assume tat everything is an HD 3.5" disk?
Not tried. I believe 720K PC disks work, and by extension Atari ST
disks, and possibly most things written by a WD FD controller chip,
but getting clever doesn't.
I have some "naughty" block-duplicated 360K 3.5" disks - imaged off
5.25" media onto 3.5" for archiving. That's an "illegal" format
-
40-track DSDD 3.5" media never existed on the PC-compatibles, AFAIK.
I'd be interested to know if they'd work on a USB floppy. Someday, I
will try.
The 720K PC disk format is identical at the cylinder level to the 360K PC
format, it's just that the former has twice as many cylinders. I assume
your archived disks simply store the contents of a 360K disk in cylinders
0-39 of a 720K disk, leaving the other 40 cylinders empty. In which case
anything that can read a clyinder or sector from a 729K disk is
physically capable of reading your archive disk (a floppy drive reads one
track at a time, so it can't know what is going on on the rest of the
disk). whether you have software problems is another matter...
I once received a 1.44M disk which turned out to contain a 720K iumage
using the first 9 sectors of each track, the other 9 conteined garbage.
This caused a lot of 'fun'... The hardwre could read it, but until I
realised what it was I had difficulty even getting a directory from it.
But it's worse than that. Things that I can
do (and do do) on my 80x86 PC
are not so easy to do on modern machines.
What x86 kit do you run?