We lost another pioneer in computing in October. John McCarthy is well know for his work in AI and LISP, but he has a close connection to the development of operating systems — John McCarthy is one of the earliest developer of time-sharing mechanism.
Lester Earnest first encountered McCarthy at MIT while working on the government’s Semi-Automatic Ground Environment (SAGE) defense system — an early computer network that allowed multiple users to access the system at the same time — and according to Earnest, SAGE inspired McCarthy’s work on time-sharing. “He was first to come up with an idea of how to do time-sharing in a general purpose way, as opposed to special purpose,” Earnest says.
You can read this article by John McCarthy that describes his early involvement in development of time-sharing system.