Extracting CDOS files

Dave Dunfield dave06a at dunfield.com
Wed Oct 10 19:16:09 CDT 2007

> 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?)

Sorry, I haven't delved back into the CDOS/CPM filesystem yet - It's been
years, and I haven't found a good technical description yet (any pointers?)

I have put ImageDisk images up at: www.dunfield.com/pub/index.htm

You can use my IMDV (IMageDisk View) utility to browse through the sectors.

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

Nope - the copy behaves exactly like the originals. Reads fine with IMD/TD,
but 22disk has trouble - Since 22disk also reports file mislinks, it's possible
that it's looking somewhere that isn't (I don't know if the Cyl1, Side1, Sec1
indication is real or logical - if logical, it might refer to a physical sector
that doesn't exist... Chuck?)

> 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've always had trouble with Cromemco disks - I find that slowing the drive
to about 290 rpm makes a huge difference in being able to read the disks.

The original machine used to create the disks is long gone, although I can
get a Cromemco machine setup if necessary - I don't relise the thought if
transferring files from a few hundred disks by serial tranfer, which is
why I would really like to get a PC based solution working...

> 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).

Thanks, anything would help. The CDOS manual has some tables at the back,
but I don't know how complete or accurate they are for all versions.


dave06a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:

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