Re: GCR <--CP/M --> MS-DOS and vice versa?

[dempson@actrix.gen.nz (David Empson)]

Tony Cianfaglione <ab616@chebucto.ns.ca> wrote:

> Could a common ground be found, using these formats, to read/write Apple
> II disks on a PC.  Since both computers can use CP/M, could software be
> written to convert MFM material to CP/M which is then written to a disk.
> The disk is then put in a II and read via software into something the II
> can understand from CP/M.  Material could be written to CP/M on teh II and
> put into a PC to translate form CP/M.
> 
> Let me guess...there is GCR CP/M and MFM CP/M and neither the twain shall
> meet? :-(

Others have covered most of the issues here and I'm coming in a little
late, but I just wanted to add one more comment regarding CP/M disk
formats.

CP/M implementations on different computer platforms tend to use
completely incompatible physical disk formats.  If machine type A and
machine type B both happen to run a variant of CP/M, there is no
guarantee that either machine will be able to read a floppy disk written
by the other one, even if the disks are the same physical size.

There is only one widespread standard format for CP/M floppy disks, and
that is the single sided single density 8 inch disk, using one of the
standard IBM formats (probably FM).  It held about 160 KB per disk,
using 128 bytes per sector, probably 40 tracks and 32 sectors per track.

This is the physical format in which CP/M was distributed by Digital
Research, and each computer manufacturer was responsible for copying the
CP/M operating system over to whatever physical disk format they used on
their platform.

Some platforms directly support an 8 inch drive, but may support their
own proprietary format in addition to the standard single density CP/M
format.  For example, we used a CP/M machine at work called the Little
Big Board, which was based around cards installed in an STD bus cage.
It supported a double sided double density 8 inch format which could
hold about 1.3 MB per disk as well as the standard CP/M SSSD.  (You
could also connect a high density 5.25" drive which held the same amount
of data as the 8 inch DSDD.)

For the Apple II, I expect that the initial setup of the CP/M variants
required connecting an 8 inch drive to the Apple II, but once the files
were copied over to 5.25" there was no need for Microsoft or the other
Apple II CP/M suppliers to deal with 8 inch disks.  Applications such as
WordStar would probably have been transferred over using a similar
one-off arrangement, with any subsequent development being done on the
Apple II.

-- 
David Empson
dempson@actrix.gen.nz