[Coco] Max number of floppy drives with DOS

[Bruce W. Calkins]

On 5/17/21 8:36 AM, rietveld rietveld wrote:
> i have 4 single sided drives connected to my coco3 .
> If I buy 4 double sided drives instead will HDB DOS see them as DRIVE 0-7 ?
> Dont want to spend the money on the drives if i can only use DRIVEs 0-3 with them
> 
> 
> Sent from my BlackBerry Key2
> 
Physically/electrically the CoCo disk controller can only operate 3 
double sided drives.  The "fourth" drive select is hacked to the 
standard side select line.  On the Disk Extended Color Basic firmware 
side the code only allows for 4 single sided drives.  Two double sided 
drives can be seen as 4 single sided drives by adjusting the drive 
address table.

RGB-DOS the predecessor of HDB-DOS did not change the format enough to 
allow more than 4 single sides to be seen by the operating system.  As 
far as I know this was not changed.

OS-9 and NitrOS9 are coded differently.  The hardware is still limited 
to 3 physical double sided drives or 4 single sided drives.  But double 
sided can be accessed as double sided drives.

Bruce W.