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

[Arthur Flexser]

Actually, I believe the extra five tracks will read fine on a 35-track setup.
You just can't save anything to the disk without destroying the FAT entries for
these tracks if you have an unmodified RSDOS, if my recollection is correct.

People were modifying RSDOS for that kind of double-sided assignment long before
ADOS since it was so easy to do--a 2-byte change is all that was needed.

Art



On Sat, 17 Feb 2007 farna at att.net wrote:

> It was common for DECB ("RS-DOS") users to modify the ROM to address floppy
> drives in the same manner. It was a very popular feature of ADOS. I believe
> some people actually hard wired the drive to work that way, but the easiest
> way is to modify the ROM code. When the ROM was modified , OS-9 could be
> booted and still use the two double sided 40 track drives as full 360K
> drives instead of two 35 or 40 track drives. Another common option used with
> ADOS was making the drive 40 instead of 35 track as well. A 40 track
> formatted disk can still be read on a 35 track drive, just the data on the
> extra five tracks couldn't be read. Of course a 40 track drive would read a
> 35 track disk.
> 
> The double sided drive as two drives and 40 track option can be poked into
> memory on the CC3 or on the CC2 (when in all RAM mode). That's good for
> temporary use only, of course. Some people just saved the pokes in a short
> BASIC or ML to make the mods when needed.
> 
> --
> Frank Swygert
> Publisher, "American Motors Cars" 
> Magazine (AMC)
> For all AMC enthusiasts
> http://farna.home.att.net/AMC.html
> (free download available!)
> 
>  -------------- Original message ----------------------
> Message: 8
> Date: Fri, 16 Feb 2007 21:50:30 -0800 (PST)
> From: Dan Olson <dano at agora.rdrop.com>
> Subject: Re: [Coco] Using a CoCo disk drive with a BBC computer
> 
> > 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?
> 
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