[fa.info-cpm] History of Modified CP/M

C70:info-cpm (08/13/82)

>From BEC.SHAPIN.USC-ECLD@Usc-Ecl Thu Aug 12 21:17:32 1982
Intel (and National) make some single board computers on the multibus with
ROM at 0.  The Naval Research Labs at Monterey (where Gary Kildall teaches)
wanted a CP/M that would run on these.  So Digital Res. first produced
an SBC version of CP/M 1.4.  This had 4000H added to everything.  Later
a version 4200H higher was produced for some Heath and Zenith systems.
This is generally what is meant by modified CP/M.  I usually write my
programs so they will run under either system. I define a base of 4200H
for modified CP/M or 0 for standard CP/M. Then
TPA EQU 100H+BASE, FCB EQU 5CH+BASE, BDOS EQU 5+BASE, BUFFER EQU 80H+BASE,
etc.

The ROM at zero can be used for permenantly resident useful programs.  Or
you can cut some traces on your SBC multibus computer, install a switch or
use a port and switch ROM in and out to run a standard CP/M system.

I don't know if D.R. ever supplied a modified 2.2 CP/M.  Modified systems
are falling into disfavor.

Ted.
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