Cromemco CDOS format (was Osborne-1 SD format)

From: Randy McLaughlin <cctalk_at_randy482.com>
Date: Mon Feb 21 16:56:02 2005

From: <mhstein_at_canada.com>
Sent: Monday, February 21, 2005 4:02 AM
>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

Cromemco kept a text string in the first sector to specify what the disk
format was. If it was missing it was assumed to be 8" SSSD.

I was always disappointed that they used such a crude method. It is simple
enough to determine what the format is.

All they ended up doing was create disks with two different formats on one
disk.


Randy
Received on Mon Feb 21 2005 - 16:56:02 GMT