[Coco] 5 1/4" drive

[Gene Heskett]

On Tuesday 07 April 2009, Bill wrote:
>Refresh my memory, please. Can an 80 track 1.2M 5 1/4" drive be installed
>into an FD-502 case and work correctly? Will it act like a "standard" floppy
>drive using the stock chip in the controller?

Yes and no.  If you can locate the jumper on the drive that slows the disk 
from the 360 rpm the 1.2meg disk spins, to the 300 rpm that all other disk 
formats spins, then they can, under os9/nitros9 only, be used for 720k drives.
I have been doing so for many years.  There is also a bit in the descriptor 
that can be set which tells the driver to double step the drive should it find 
a 40 track formatted disk in it.  This is ok for reading ONLY, do not attempt 
to write to that disk as the write, due to the narrower heads of the 80 tpi 
format, will not fully erase the old data in the wider 40 tpi track, and the 
disk will be forever trashed for reading in a real 40 tpi drive.  Until its 
formatted again.

With those caveats, it will work fine.  The reason you can't get the 1.2 meg 
size is that requires a 500 kilobaud data stream between the controller and 
the disk, and the WD177x family of fdc chips used in 99% of the coco disk 
controllers cannot run that fast. 250 kilobaud is the designed speed of those 
chips.

>Thanks
>
>
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-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
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Write-only-memory subsystem too slow for this machine. Contact your local 
dealer.