[Coco] 1.2 mb floppy

[Gene Heskett]

On Friday 11 May 2007, mike delyea wrote:
>Can I use my 1.2mb floppy with OS-9/NitrOS-9?  Could I split up my
>1.2mbfloppy into 2 720k drives or 4 360k drives?  I read somewhere
>that you
>couldn't use the 1.2mb floppy to write coco or OS-9 360k disks.  This
>doesn't seem to be true because I used my 1.2mb to write my NitrOS-9 disks
>from an image.  Does anybody know it the dmode numbers for the step rate are
>the actual step rate?  For example is stp=03 a 3ms step rate and so on.
>Whats the fastest step rate thats usable?  Thanks for your help so far.

This is almost correct, the 1.2 meg is done by a combination of speeding the 
drive up to 360 rpm from the normal 300, and doubling the baud rate to/from 
the media to 500kb/second.

Its this last that the coco can only do with one controller, and it has to be 
modified quite a bit.  The original one that needed 12 volts too is the only 
one.  So on a coco3, it has to be run in an MPI in order to get that 12 
volts.

Without that, you are stuck at the default 250kb/second data rate, which on an 
80 track 300rpm drive gives you 720k of storage.

Note though, that most of the 1.2 meg drives can be slowed down to 300 rpm 
with a jumper on the drive board, and they then make excellent 720k drives, 
I've done that to several over the years.

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Cheers, Gene
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