[Coco] OS-9 and RS-DOS disk structures

[Robert Gault]

Allen Huffman wrote:
>> On Dec 30, 2014, at 9:50 PM, Robert Gault <robert.gault at att.net> wrote:
>> The double sided OS-9 disks alternate tracks such that all the even tracks are on side one and all the odd tracks are on side two of a floppy. The default format for emulators is to alternate the "front" and "back" tracks which is easy to see if you examine the .dsk/.os9 images.
>
> Hmmm. If I have a disk in my CoCo, and it is POKED to DRIVE 0 is the normal side of my bottom drive, and DRIVE 2 is the back side of the same drive, then I write
>
> Track 0, sectors 1-18 with 0s...
> Track 1, sectors 1-18 with 1s...
> ...
> Track 34, sectors 1-18 with 34s...
>
> Then I go to DRIVE 2 and do something like 100s, 101s, 102s, etc...
>
> As OS-9 would read sectors, it would see track 1 be 0s, then track 2 be 100s, then track 3 be 1s, then track 4 be 101s? Am I seeing that properly?
>
> Then if I was making a .DSK image file for OS-9, would I write it out that same way?
>

Well you could but why go to the trouble? :) Also it would help if you stated 
your final objective rather than asking about what you think would be the best 
method of achieving the non-mentioned goal. That would permit us to respond to 
the actual goal.

So, let's say you just want to copy real double-sided OS-9 disks to second disk. 
If that is the goal, just use BACKUP from Disk Basic or backup from OS-9.
Disk Basic with 0=front and 2=back Drive A, 1=front 3=back Drive B
You would just
10 BACKUP0TO1
20 BACKUP2TO3

OS-9
Format a second disk for the same number of tracks and side as the original and 
then    backup /d0 to /d1

Generally problems arise when trying to copy real disks to images. You need to 
be able to create the needed image on your PC and have a mechanism to transfer 
data between the Coco and PC.
The simplest methods would require a 5.25" drive on the PC and the VCC emulator. 
Or both 3.5" and 5.25" drives on the Coco (to convert disk format) and a 3.5" 
drive on the PC. VCC can read real floppies on a PC.
Alternatively, Drivewire can be used to create disk images and transfer data but 
it is much more complicated unless you already have a Drivewire ready version of 
OS-9 on the Coco.
A final brute force method would be to create say 35-track single sided disk 
images on Drivewire and with the Drivewire HDBDOS ROM on the Coco, backup the 
front and back sides of disks to separate images. Then you can use an emulator 
to backup the separate images to a final double sided image.

I think you have said you do not yet have OS-9 running on the Coco. What 
utilities and emulators do you have on your PC? What disk ROM is in the Coco? If 
this is too involved to handle via the list, you can send email directly to me.

Robert