[Coco] HDB-DOS Eprom

Robert Gault robert.gault at att.net
Fri Mar 18 14:55:10 EDT 2016

Louis Ciotti wrote:
>> Do you want an extended basic drive offset programmed? If so what offset
> do you want?
> Being a newbie on HDBDOS what is this for?


HDBDOS will work with real hard drives and hard drive images (.vhd). The most 
prevalent .vhd image used with the emulators JVC, MESS, and VCC assumes the 
first part of the .vhd is for OS-9 and the latter for Disk Basic. This hard 
drive image consists of $5A000 bytes allocated to OS-9/NitrOS-9. The rest of the 
image consists of 256 Disk Basic "disks" which are 35-track, single sided.

All versions of HDBDOS contain a three byte offset value at $D938-$D93A which 
indicates the amount of space allocated to OS-9. The copies of HDBDOS available 
on the Internet generally have an offset value of $00000 which means that the 
hard drive image disk.vhd does not have an OS-9 section.
Of course any of the 256 disks in the Disk Basic section could be OS-9 disks but 
that is not what is referred to above.


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