[TUHS] PDP-11 questions

Ronald Natalie ron at ronnatalie.com
Mon Jan 25 23:25:46 AEST 2016

> A random vaguely off-topic example: in Cambridge a PDP-11 was used as a
> terminal multiplexor for the IBM mainframe.

BRL had a PDP-11/40 that was running software called ANTS (Arpanet Terminal Server) written by the University of Illinois.   It was amusing in that it put the time on every message it printed on the terminal.   It has a “time” command that printed “is the time” (in case you didn’t know what those numbers were).    It also had silkscreened ants on the logo panels (which were orange rather than the original DEC purple and red).     The software became obsolete when the ARPANET went to long leaders.   Mike Muuss’s standard answer was to put UNIX on the machine and so it ran UNIX from December of 1980 up until the TCP/IP cutover.    I kept the ANTS logo’d racks as being kind of cool but had a hard time explaining to the Army what this $65,000 of computer equipment was I was disposing of.

The system I started on at JHU had run RSTS until Mike and friends convinced the EE department that they could get BASIC PLUS to run under UNIX on the PDP-11/45.    This turned out not too be too hard.   Despite what the processor handbook said you were supposed to use, DEC always used EMT for their system calls.    UNIX followed the guidance and used TRAP.   This made it a lot easier.

I had experience around the university running DOS/BATCH (anybody remember that phone book of a manual) and RT-11 on things like 11/20s and the original LSI-11s that really couldn’t run a full up UNIX.    I even worked on this dreadful Heathkit H-11 with it’s awful H-9 terminal (no preprinted keycaps you stuck labels to the blanks for the letters and it’s the only UPPER CASE ONLY terminal I ever saw that you had to run LCASE mode on because if you sent it lower case letters rather than just upshifting them it printed gibberish instead).

My first job after college was writing database for a government project using two connected RSX-11M systems, but we had a third system that I installed PWB UNIX on (OK well it was IS/1) and used that as our source code control system for the RSX system (we also did all our docs in nroff on the system where I had hacked the -mm macro package to handle security classifications).

When UNIX got too bloated for PDP-11s I recycled most of them into internet routers.   I did use one as an IO control processor for the Denelcor HEP system we had.   The HEP had 32 individual UNIBUSes connected to the IO memory and an 11/34 had the job of reflecting the IO requests from the HEP itself back onto those unibuses.
It ran the same “Little Operating System” that the routers did.

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