Tymshare’s Changes to the Project Genie SDS-940 Operating System: A Historical Review

The University of California’s Project Genie was an ARPA sponsored project to create an interactive programming environment. The SDS-930 was a relatively inexpensive machine with a maximum of 32 K of physical memory. To create a time-sharing machine from the base SDS-930 architecture, Pirtle and Lichtenberger extended the ’930 architecture to include protection and memory mapping. Deutsch and Lampson implemented an operating system for the modified ’930. Ultimately, SDS decided to market the Berkeley modifications to the ’930 and denoted it the ’940. They sold the machine to a new company called Tymshare. Tymshare heavily modified the Berkeley operating system over more than five years. Utilizing the system call manuals and the source code from Tymshare, it is possible to trace the operating system modifications that parallel the development of disk and telecommunication hardware in the late 1960s and early 1970s. It also illustrates what is required to turn a prototype system into a hardened commercial success.