Extracting CDOS files

Fred Cisin cisin at xenosoft.com
Tue Oct 9 15:41:43 CDT 2007

> > Mask out the index pulse if all you're going to do is read.  22Disk
Definitely, but it still doesn't work sometimes.

On Tue, 9 Oct 2007, Dave Dunfield wrote:
> Hi Chuck,
> Thanks for the suggestions.
> I was told that these are DSDD CDOS diskettes, and reading them with
> ImageDisk gives me double density on both sides except for the first
> track which is single density.
> The shareware 22disk has four Cromemco types:
>   CRO1 Cromemco CDOS - SSSD 48 tpi 5.25"
>   CRO3 Cromemco CDOS - SSDD 48 tpi 5.25"
>   CRO4 Cromemco CDOS - DSDD 48 tpi 5.25"
>   CRO6 Cromemco CP/M - SSDD 48 tpi 5.25"
> Of these, CRO4 (and only CRO4) gives me what looks like a readable
> directory with reasonable filenames. However it reports that files
> have cross-linked blocks.

That is likely to be a slightly different format than what you've got.

Can we see hex of the 32 bytes of some of the directory entries,
preferably with a LARGE file?

IIRC, Cromemco used at least 3 different ways of handling extended entries
for large files.
Do you have access to how many records per block?
How many blocks per extent?
(Is the block number stored as 8 or 16 bits?)

> Masking out pin 8 (Index) on the 34-pin connector has no effect, I
> still get:
> Error reading diskette B: (Cyl 1, Side 1, Sect 1)
> Sector not found
> This sector DOES exist, both ImageDisk and TeleDisk can read it fine,
> however no amount of "Retry" will convice 22disk to read it.

Can you use ImageDisk or TeleDisk to copy the sector contents, to produce
a "copied" disk that has readable sector 1s?

IIRC, some CDOS variants (there were several) had a skew, resulting in
some other sectors on the disk being hard to get at.

If the Cromemco machine is still in existence, they don't seem to mind
disks that have reasonable gaps, so long as you get the flag in the "boot
sector" to show the correct disk size.

> I'd try my hand at extracting the files from the images, however this
> isn't going to be easy due to the "invisible" sector interleaving...
> hopefully the tables in the back of the CDOs manual are correct.
> Unfortunately ALL the files on the three sample disks I have are
> binary in nature, so I can't easily tell if I actually got the right
> data (as you usually can with a readable text file).

I probably won't have access to any of my stuff in the next week or two,
but I can eventually get my notes of the CDOS interleave pattern(s).

Good luck,
Grumpy Ol' Fred     		cisin at xenosoft.com

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