MOS operating system

The MOS operating system (formally the 'Micro Operating System', but informally 'Mathis' Operating System', after the creator, Jim Mathis) was an operating system, originally for the PDP-11 used for a number of packet switches and similar network applications.

The original version was written in MACRO-11, the assembly language for the PDP-11; it supported processes (but not premption, or creation/termination of processes), allocation and freeing of main memory, asynchronous I/O, and inter-process messages.

It was later re-written at least three times in C: at BBN, at UCL, and at Proteon. The latter version was portable, and also ran on the MC68000 and AMD29000. All were somewhat extended from the original; the first two fairly extensively, the latter only to make use of up-calls in the I/O system.