From: utzoo!decvax!ucbvax!C70:info-cpm Newsgroups: fa.info-cpm Title: History of Modified CP/M Article-I.D.: ucb.1759 Posted: Thu Aug 12 21:17:45 1982 Received: Sun Aug 15 03:31:16 1982 >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. -------