[Coco] Reading CoCo Disks

[Gene Heskett]

On Monday 14 September 2015 11:18:25 Michael Brant wrote:

> I recently aquired an XP desktop and have a 1.2 mb 5.25 in floppy
> drive in it.  Are there any programs for reading and writing either
> RSDOS or OS9/NITROS9 disks?
> Thanks,
> Mike

That drive would not normally be recommended for coco/nitros9 use.
It, first off spins at 360 rpm, as oppsed to the usual 300, and needs a 1 
megabaud capable controller, which it has in the XP machine.

Its heads read and write a track only half as wide as the coco/nitros9 
std diskettes and drives use.  So the nearest to a coco compatible 
format it can do is to duplicate the 80 track DS 720k format that only 
nitros9 can handle.  Std coco's cannot read those additional tracks.

This would be accomplished by slowing it to 300 rpms, and writing in the 
80 track per side format, at a data baud rate of 250 kilobaud in order 
to match the data rate a coco controller can handle.

Sure, it can be made to double step and thereby do a 40 track (or even 35 
SS), but the narrowness of its heads means theres a lot of empty space 
between tracks that is not erased, leaving  all sorts of garbage to be 
read by the wider heads of the standard coco drive.  IOW, it doesn't 
work.

It can be done, but requires a complete bulk erasure of the diskette 
before its written in that format. Doable I find only by a commercial, 
dims the lights, bulk tape eraser that needs a 20 amp circuit to 
function, it will trip a 15 amp breaker in a second or less.

I have one of those drives, a single spindle that does 5.25" on one end, 
and a HD 1.44 meg 3.5 on the other all in one half height package.  Very 
rare drive I think, and totally unusable on this linux box because the 
FD chip cannot to a 256 byte sector, locking up this fancy Asus 
motherboard, responsive only to the reset button and a reboot to recover 
from the attempt.

Cheers, Gene Heskett
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