[Coco] Using a CoCo disk drive with a BBC computer

[Phill Harvey-Smith]

Dan Olson wrote:
>> The BBC uses standard drives either jumpered as DS0 or DS1 (it can only
>> normally have 2 drives, a restriction of the firmware), however the way
>> these are handled is quite clever.
>>
>> side 0 of first drive is drive 0
>> side 0 of second drive is drive 1
>> side 1 of first drive is drive 2
>> side 1 of second drive is drive 3
> 
> Very strange, it seems like this would have the disadvantage of limiting 
> the max file size and adding more complexity to file management, with no 
> real advantage.  Is this a result of the DOS or is it hard coded in a ROM 
> somewhere?

Pretty much hard coded into the DFS (dos) ROM, but as I said before it 
has the advantage that if you format drive 0 in a double sided system, 
you don't have to remember to specify that the disk needs to be single 
sided if you want to exchange data with a single sided system.

Also as someone else pointed out RS-DOS also hard codes single sided 35 
track disks. DragonDos and clones are slightly more flexible in that 
they support single or double sided 40 or 80 track disks, but again 
these 4 formats are hard coded into the ROM.

Also I guess back in 1980/81 when this was designed it was not thought 
that users would want to generate files that where bigger than this 
scheme could cope with. Though IIRC there was later ADFS (Advanced Disk 
Filing System), which could cope with bigger files, hard drives etc.

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.