Berkeley Time-Sharing System
From Computer History Wiki
Time sharing operating system for an enhanced SDS 930. Primarily written by L. Peter Deutsch, Butler Lampson, and Chuck Thacker.
It had an influence on the early design of UNIX; Ken Thompson was very familiar with it, and some aspects of Unix (e.g. the split between fork() and exec()) copy how the Berkeley system operated.
Supposedly, it featured a limited version of PCLSRing.
