2 Oct
1998
2 Oct
'98
10:58 a.m.
On Fri, 2 Oct 1998, Tony Duell wrote:
Also, early versions of PC-DOS (<3.10?) had an appendix with it.
It's important if you need to repair damaged disk structures, or if you
are trying to write an alien file system handler (such as to read or
write MS-DOS disks on some other kind of machine.
Are you
looking for the DIRectory structures, track layout (sector
headers and the like), or explanation of MFM?
The former is probably in some books
on MS-DOS system programming, or
possibly read the Linux MS-DOS filesystem source code or something like that. The second is in the disk controller data sheets
(Intel 8272, NEC 765,
etc), although IMHO they don't explain it that well. Figuring out exactly
what sequence of pulses was a data marker was interesting, for example.
The last is probably also in some of the disk controller data sheets,
although I can't find it at the moment.
At least some of the Shugart drive technical reference manuals have it.
For those in the SF Bay area, look for a UC Extension course held in Palo
Alto by Mark Young, entitled "Floppy and Winchester Disk Controller
technology". GREAT course, and explains below sector level issues quite
well.
In general you only need the last 2 levels if you are
trying to make a
disk controller or make sense of the raw data stream from the drive on a
logic analyser.
Or, with access to clock and data, trying to repair sector headers, CRC
errors, etc.
You don't need to know this to talk to the disk
controller registers - you tell the chip to read a sector and it does so.
The disk controller handles finding the sector, stripping off the header,
checking the CRC, etc.
Certainly a much more civilized and sensible way to do things. But some
of us are crazy enough to forego that level of sanity.
Post them here. They are related to machines over 10
years old, aren't they?
I'm going to look for some files that I had poreviously written, so as
not to have to redo. >10 years old? Oh, yes. Nothing much has changed
in longer than that. (And that's when I wrote those files)
--
Fred Cisin cisin(a)xenosoft.com
XenoSoft http://www.xenosoft.com
2210 Sixth St. (510) 644-9366
Berkeley, CA 94710-2219