[Coco] Drivewire, NitrOS9, and floppy drives

[Robert Gault]

Willard Goosey wrote:
> On Wed, Apr 08, 2009 at 09:58:44AM +1000, Bob Devries wrote:
>> Unless someone has OS9 formatted disks which are set up as a separate disk 
>> (such as the Rainbow OS9 on disk), accessing the back side of a disk is not 
>> really useful.
> 
> Those were flippies, weren't they?
>> It's much more useful to use the entire disk as a single unit, both the 
>> lower and upper heads of the drive.
> 
> I suppose that might be useful to access both sides of a double-sided
> DECB disk written with one of the DOS patches, but other than that, I
> gotta agree.
> 
> Willard

Keep in mind the history of OS-9. The Coco started out as Disk Basic 
only with no provision for double sided drives. Hackers then realized 
that with a change of the drive masks, one could double the disk space 
by using the back side of disks.
When OS-9 LevelI was released, Tandy was still assuming single sided 
drives. Once again, disk space could be doubled by changing the drive 
masks. Look through "The Complete Rainbow Guide to OS-9" by Puckett and 
Dibble and you will find a discussion of this on page 156.
LevelII or maybe LevelI version 2, contained a driver that correctly 
handled double sided disks. Now users had a choice of how disks should 
be formatted, but old disks formatted as two singles might still need to 
be used.

Depending on the number of floppy drives attached to your system, it 
does no harm to alter the drive masks. If you have only two drives, /d0 
and /d1 can be set for true doubles while /d2 and /d3 can be the back 
side of the drives. Then any variety of Coco disk can be read.
If you have more than two floppies, you may want to stick with true 
doubles. However, you can be more creative than that.
You can increase the number of "drives" that rb1773 handles from 4 to 6, 
maybe 7. The drive mask table would be $01,$02,$04,$40,$41,$42,$44. That 
  could give you /d0 /d1 and /d2 as true doubles, /d3 would be a single 
sided drive, /d4 /d5 and /d6 would be the back sides of /d0 /d1 and /d2.