Extracting CDOS and CP/M) files - test-drb@ccmp.vtda.org

11 Oct 2007

---------------Original Message:
Date: Thu, 11 Oct 2007 10:58:08 -0700 (PDT)
From: Fred Cisin <cisin at xenosoft.com>
Subject: Re: Extracting CDOS and CP/M) files
To: "General Discussion: On-Topic and Off-Topic Posts"
	<cctalk at classiccmp.org>
Message-ID: <20071011105050.V71651 at shell.lmi.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII

...
  > CDOS had one or more bytes in the first physical
sector of the disk to
 > identify which format.  There ARE multiple (user modifications?) variant
 > formats that may have the same ID byte(s)! 
On Thu, 11 Oct 2007, Dave Dunfield wrote:
...
  Anyone have more info on this? - One of my main
problems is determining
 exactly what format these disks are in. 
It might be stored in the first sector, or it might be known only to the
OS.
On a functioning CP/M 2.x? machine, STAT DSK: gives some of the
parameters.

...
  Does each entry represent a cluster? Yes, each
of the numbers in the block list represents a "cluster" (which
is the MICROS~1 word for a block)  Each OS company seems to have had their
own unique word (like "standards") for an allocation unit.

Remember that CP/M calls a 128 byte record a "sector" disunirregardless of
how many there are in each physical sector.

-----------------Reply:
On a Cromemco disk (including HDs) at offset 0070H there are 6 bytes that
indicate CDOS or Cromix format, Single or Double density and S/D sided,
and these are all options in the format (init) program. This is why track 0 is 
formatted as the lowest common denominator (SD) for all floppies, so that 
the controller can start with a known format and then decide how to handle 
the rest of the disk. Hard disks indicate type (IMI/MFM) instead of SD/DD & SS/DS.

The first (dummy) directory entry of a CDOS floppy contains the 8 character 
disk ID, the date it was formatted and the number of directory entries.

The remaining parameters (disk size, interleave vector table, etc. are stored
in the BIOS the same as CP/M AFAIK; hard disks keep size &c on the disk
(along with partition & alternate track tables) so that you can swap disks
without reconfiguring anything.

mike