Cromemco CDOS format (was Osborne-1 SD format)

From: mhstein_at_canada.com <(mhstein_at_canada.com)>
Date: Mon Feb 21 04:02:46 2005

A little more about Cromemco disk formats, from my limited
knowledge:

In case it isn't obvious, the reason for the "non-standard"
format (was there a "standard" format in those days?) is to
be able to read/write all four formats interchangeably.

Track 0, side 0 is formatted to the lowest common denominator,
SS/SD, so all systems can read it no matter what the format of
the rest of the disk may be. At the end of sector 1 (78-7Fh)
it finds the format information for that disk (5" or 8",
single/double sided,single/double density, and CDOS or Cromix,
conveniently in ASCII, e.g. SMDSDD=SMall (5 1/4", CS if it's
Cromix) DS,DD. Then it can read/write the rest of the disk
accordingly.

Hard disks are handled similarly, although density is irrelevant:
The system finds the hard disk id at the same offset as on the
floppy, and the hard disk configuration (cylinders, surfaces,
sectors per track, bytes per sector and location of the alternate
track table) immediately preceding it; thus you can plug in any hard
disk with a compatible interface and the system can read the
geometry etc. off the disk by reading the first sector regardless
of the disk layout, since no hard disk will have < 128 bytes in
the first sector.

mike
Received on Mon Feb 21 2005 - 04:02:46 GMT