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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