Osborne-1 SD format

From: Dan Lanciani <ddl-cctech_at_danlan.com>
Date: Mon Feb 21 17:55:40 2005

|With a PC format disk, and most other DD disks, I can simply issue
|a "read id" with the wrong data type - this times out at the index
|hole after two revolutions, at which point I set the right data type
|and perform repeated "read id"s until I see the same id again - on
|most disks, this quite reliably gives me the sector interleave pattern
|on the track.
|
|With the Cromemco disk, this does not work, as often I won't see all
|of the sector id's until I have reissued the "read id" many times,
|often seeing some sectors 30-40 times before seeing one occurance of
|the "tough" sectors. Clearly even if I do eventually get all the
|sector Id's, I cannot determine what the interleave is at all..., not
|to mention that this makes the "analysis stage" a but lengthy.

Try adding an increasing small delay after the read id you use to
synchronize with the index hole.

|(read-track seems
|pretty useless on the 765 series).

It is. Your best bet would be to get a 1797 family controller.

|It's interesting with the Cromemco CDOS disk - the DD area is formatted
|to 10 512 byte sectors/track, and in the DD(360k) drive, I can't read
|them at all - For this test, I pulled the actual Teac drive that I have
|been using on the System-3 (which reads it fine) - it looks like the PC
|controller has touble with the tightly spaced sectors.

It has trouble with various kinds of back-to-back operations, but I
wouldn't expect that to make the tracks totally unreadable. Something
else is going on. Is it possible that the BIOS thinks you have an
80 track drive and is double-stepping? That would let you read track
0 but no other.

|It (the DD drive) can however read all of the SD sectors in track-0
|just fine!
|
|The HD drive reads the entire disk perfectly, EXCEPT for Sector-1 of
|Track-0 (the SD track) - it quite reliably refuses to read the first
|sector of the SD track. The remaining sectors of the SD track and all
|of the DD tracks read OK.

Try covering the index hole cutout on the disk or otherwise blocking the
drive's index sensor. The controller does not like to start a read too
close to the index hole, but it will mostly work without any index pulses.
(It won't format or timeout of course.)

                                Dan Lanciani
                                ddl_at_danlan.*com
Received on Mon Feb 21 2005 - 17:55:40 GMT