The RC 4000 system, like the THE system, was notable primarily for its design
concepts. It was designed for the Danish 4000 computer by Regnecentralen,
particularly by Brinch-Hansen (Brinch-Hansen [1970], Brinch-Hansen [1973]).
The objective was not to design a batch system, or a time-sharing system, or
any other specific system. Rathel~ the goal was to create an operating-system
nucleus, or kernel, on which a complete operating system could be built. Thus,
the system structure was layered, and only the lower levels-comprising the
kernel-were provided.
The kernel supported a collection of concurrent processes. A round-robin
CPU scheduler was used. Although processes could share memory, the primary
communication and synchronization ITl.echanism was the
provided by the kernel. Processes could communicate with each other by
exchanging fixed-sized rnessages of eight words in length. All messages were