[Coco] OS-9 Floppy

[Robert Gault]

Melanie and John Mark Mobley wrote:
> Can I write a DECB (Disk Extended Color BASIC) file to an OS-9 disk without
> disturbing the OS-9 portion of the disk?
>

It is possible to format a disk for both DECB and OS-9 but you need much manual 
work to get it right. It is only practical if you force the first half of the 
disk to be OS-9 and the second half to be DECB.

Here is how you must do it to get it to work. Format the disk for OS-9 as a 
single sided disk. Now use dEd to mark as used the allocation bit map in LSN1 so 
that OS-9 can't make use of track 17 and beyond. So fill LSN2 bytes $26- with $FF.
Now format a different disk with DECB. Place the OS-9 disk in drive0 and the 
DECB disk in drive1. Run the following program.
10 CLEAR 512
20 FOR S=1TO18
30 DSKI$1,17,S,A$,B$:DSKO$0,17,S,A$,B$
40 NEXT
That will place a DECB directory onto the OS-9 disk. You now need to mark the 
file allocation sector T17S2 to show that the sectors used for OS-9 are not 
available. You can write a DECB program to do this but using a raw disk editor 
is easier. Again assuming the first half of the disk is OS-9 fill T17S2 bytes 
0-$21 with $EE to mark it used.

Now you could right either a Basic09 or DEC Basic program to do the above but it 
probably won't be worth the effort. Why not put OS-9 on the front side of the 
disk and DECB on the back side of the disk?

Robert