RC 4000 multiprogramming system
The RC 4000 Multiprogramming System was an operating system developed for the RC 4000 minicomputer. It is historically notable for being the first system to break down the system into a group of interacting programs communicating via a message passing kernel. Although RC 4000 itself was not very successful it had a tremendous effect on research efforts, sparking the microkernel concept that dominated operating system research through the 1970s and 80s.