Ah, RSTS...the Really Sh-ty Timesharing System.     An amusing UNIX story on that one.   Hopkins EE department was a RSTS shop running primarily the Basic Plus interpreter which was the core of some classroom courses (especially the Freshman course:  Modeling and Simulation).   When the the guys found out about UNIX they lobbied the department faculty to switch to UNIX and they were told they could provided that Basic Plus continued to run.

Amusingly, if you read the DEC processor handbook, it says the TRAP instruction is designed to invoke system calls.    UNIX did this of course.   Amuslingly, the DEC operating systems, including RSTS, used EMT to invoke system calls.   The book says this was put there to allow emulating other OSs.    Well this made it relatively easy.

Basic Plus was calling EMT so they just had to catch the EMT traps and emulate the few RSTS calls that Basic Plus needed to make.    JHU/UNIX was born.   It was a Version 6 UNIX (which original system administrator John Day decided that 6.06 was a great version number and he kept it through many software updates).    Mike took over and stared advancing the numbers again.

We also had an 11/40 (lacking memory management) running miniUnix.   They also ran miniUNIX in the Biomedical engineering lab on an LSI-11/03.    I upgraded that lab to 11/23 running full up UNIX later on.

You may recall that the UID was stored in a (unsigned) char in those days.   This was problematic when you had a student body of a couple of thousand.    The solution was a kludge:  "JHU Ownership."     If your GID was over 200, both your UID and GID were considered when computing identity.    Obviously, newgrp was disabled for those accounts and I spent many an hour trying various combinations of setuid/gid bits and setuid/gid calls to see if there were any way to abuse that.