[Coco] CocoSDC booting OS9

[Robert Gault]

Brett Gordon wrote:
><snip>
> Usually, I think most user partition there HD's with OS9 at the beginning,
> and HDBDOS *after* it.  With Boisey's Super Driver for OS9 you can
> partition the drive the other way around with HDBDOS drives taking the
> lower partition and OS9 the higher. If you format your HD this way, then
> you have the ability to create a bootdisk that is readable from HDBDOS (and
> the DOS command) solve the Bob's proposed dillema.
>
><snip>

Maybe you can place the Basic portion first and OS-9 last with the Super Driver 
but that would NOT be good. Further there is no reason to do that with HDBDOS.

RGBDOS and HDBDOS start in Disk Basic mode and read Basic disks based on the 
offset at $D938-$D93A in the Disk ROM. If you want just Disk Basic then the 
offset (stock I believe for HDBDOS) is $000000. The default for the emulators 
JVC, MESS, and VCC is $5A000.
You can backup a 35-track single sided NitrOS-9 disk to any of 256 drives after 
the $5A000 break and boot into NitrOS-9 from that disk. It just requires the 
correct Boot module and the program LINK.BAS to correctly set LSN0 in the 
NitrOS-9 portion of the .vhd drive.
There should not be any reason why the SDC can't work this way and be compatible 
with all other Coco installations including real hard drives with RGBDOS.
Also, if you don't like Disk Basic, you can have HDBDOS automatically boot into 
NitrOS-9 on startup with the use of only 1 or 2 Disk Basic "drives" on the hard 
disk.

With real hard drives, the offset is set by the user based on the size of the 
drive and the desire or lack of it for OS-9 or Disk Basic. The original code 
RGBDOS was written when drives were small; not like todays monsters. :)

Robert