[Coco] Virtual disk file formats

[Robert Gault]

Salvador Garcia wrote:
> Thanks Dave and Bill,
>
>
> Aside from wanting to learn more about these formats, I am curious as to ho people create these and then put them on Websites so that others can download them and mount them on VCC (or other). For example, a few months ago I downloaded an image recommended by some one here with NitrOS9. I mounted it on VCC as a hard drive. Now when I start VCC I get a menu that allows me to either drop into BASIC or load NitrOS9. That is what started to make me wonder how these images are created (and how it auto run when VCC starts, but that is another topic)-
> ***************************************************************************************************
> I further wanted to know how I could create these images with my own BASIC programs that I can load and run within VCC and further on, with DW4, especially if I do not have any CoCo hardware that I can "rip" to create the images. Thanks again to both! Salvador
>
> ***************************************************************************************************

Creating .vhd images is simple with either VCC or MESS. You just create a 0-byte 
file, ex.  MyDisk.vhd , and mount it in either VCC or MESS.
When you start emulation, you will want to expand the .vhd to full size which 
you can do with a Basic program assuming your RGBDOS/HDBDOS ROM has the offset 
set to $5A000 at $$D938.

10 POKE &HD938,5:POKE&HD939,&HA0:POKE&HD93A,0
20 FOR DR=0 TO 255
30 DSKINI DR
40 NEXT DR

You can now access all the 256 Basic drives but will not have access to the OS-9 
portion of the .vhd as it is filled with $00. So you will need to use a 
distribution disk that can access an emu type drives so you can format the OS-9 
portion of the .vhd disk.
You will need the eumdsk driver and descriptor to access the .vhd from VCC or 
MESS. Format the .vhd which will be /H0, and fill the CMDS directory with the 
current commands.
You will now want to create a 35-track, single sided boot disk, which can be 
backed up to one of the 256 drives on the .vhd disk so that you can boot into 
NitrOS-9 directly from the .vhd. Alternatively, you could cobbler the .vhd disk 
but then you would boot into it using a ROM with a $00000 offset.

Robert