On Fri, Apr 9, 2021 at 11:34 PM Ed Bradford <egbegb2 at gmail.com <https://minnie.tuhs.org/cgi-bin/mailman/listinfo/tuhs>> wrote: Some knowns/givens at the time ... 1.) He was a language/compiler type person -- he had created PL/M and that was really what he was originally trying to show off. As I understand it and has been reported in other interviews, originally CP/M was an attempt to show off what you could do with PL/M. 2.) The 8080/Z80 S-100 style machines we quite limited, they had very little memory, no MMU, and extremely limited storage in the 8" floppies 3.) He was familiar with RT/11 and DOS-11, many Universities had it on smaller PDP-11s as they ran on an 11/20 without an MMU also with limited memory, and often used simple (primarily tape) storage (DECtape and Cassette's) as the default 'laboratory' system, replacing the earlier PDP-8 for the same job which primarily ran DOS-8 in those settings. 4.) Fifth and Sixth Edition of Unix was $150 for university but to run it, it took a larger at least 11/40 or 45, with a minimum of 64Kbytes to boot and really need the full 256Kbytes to run acceptably and the cost of a 2.5M byte RK05 disk was much greater per byte than tape -- thus the base system it took to run it was at least $60K (in 1975 dollars) and typically cost about two to four times that in practice. Remember the cost of acquisition of the HW dominated many (most) choices. *I**'ll take a guess, but it is only that.* I *suspect* he saw the S-100 system as closer to a PDP-11/20 'lab' system than as a small timesharing machine. He set out with CP/M to duplication the functionality from RT/11. He even the naming of the commands was the same as what DEC used (*e.g.* PIP) and used the basic DEC style command syntax and parsing rules.