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
Received on Mon Feb 21 2005 - 17:55:40 GMT

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