Mail Archives: opendos/1997/02/04/13:37:07
> MP/M and CP/M 3.0 were a big problem. MP/M is a multiuser version of CP/M;
> it's larger than 6,656 bytes just for the parts distributed by Digital
> Research, let alone the customized BIOS needed to make it run on your
> hardware. CP/M 3.0 added disk caching, passwords, time stamps on files, and
> lots of other goodies to CP/M; it was also quite large. But the average
> customer still needed to be able to use his old disks, which only had the
> meager space set aside for CP/M 2.x. There was just no way to cram the
> new operating systems into the reserved space on the old disks.
>
> To deal with this, Digital Research came up with a stripped-down read-only
> version of CP/M called MPMLDR (for loading MP/M) and CPMLDR (for loading
> CP/M 3.0). This was small enough to fit in the old reserved space and
> functional enough to find the _real_ operating system on disk and load it
> into memory.
On my CP/M 3.0 system (yes, I still have it!) it has 512-byte sectors,
9 per track. That gives 9216 bytes in the two reserved tracks. Of
this, 2048 bytes is used for the directory (64 entries of 32 bytes
each), giving 7168 bytes (7K) for code. The file which this then
loads is around 24K, and is loaded into extra memory banks which are
mapped in and out of the machine's 64K address space as needed. I
also have some CP/M 2.1 disks lying around. In these, the entire OS
does indeed fit within 7168 bytes.
Mind you, I don't boot off a floppy any more. I've put the OS (along
with some patches for things like my serial port, 3.5" disks, etc...)
into ROMs. Two ROMs contain CP/M 3.0, CP/M 2.1, and the patches, AND
a menu program to select which OS and patches to load.
Nowadays, I'm afraid I only use CP/M to load a terminal emulator and
connect via a serial link to a Linux box. But with the sources,
maybe I could play with it some more ...
-- David Cantrell, http://www.eimages.co.uk/users/davidc/
Power is both corrupting and dangerous when unchallenged and
concentrated in the hands of the majority. Voices of tolerance
and compassion are easily drowned.
-- Akbar S. Ahmed
- Raw text -