> 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:
> 
> > Why did a Ph.D., an academic, and a computer scientist not know about UNIX
> > in 1974 or so? 1976? In 1976, some (many?) universities had source code.
> >
> 
> 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.

That is about it. CP/M predates the Altair / S-100 bus, and was designed for a heavily hacked Intellec-8 system.

CP/M was developed on a PDP-10 based 8080 simulator in 1974. It was developed for the dual purposes of creating a “native” PL/M compiler and to create the “astrology machine”.

The first versions of CP/M were written (mostly) in PL/M. To some extent, in 1974 both Unix and CP/M were research systems, with a kernel coded in a portable language — but aimed at very different levels of hardware capability.

In 1975 customers started to show up and paid serious money for CP/M (Omron, IMSAI) - from that point on the course for Kildall / DRI was set.

The story is here: https://computerhistory.org/blog/in-his-own-words-gary-kildall/?key=in-his-own-words-gary-kildall <https://computerhistory.org/blog/in-his-own-words-gary-kildall/?key=in-his-own-words-gary-kildall>