MOS operating system
The MOS operating system (formally the 'Micro Operating System', but informally 'Mathis' Operating System', after the creator, Jim Mathis of SRI) was a cooperative multi-tasking operating system, originally for the PDP-11, used for a number of packet switches and similar network applications. It was almost certainly written as part of the Terminal Interface Unit or Port Expander projects (likely the former), the first two applications which used it.
It supported processes (but not preemption, or creation/termination of processes - all processes were created at system linking time), queued inter-process messages, asynchronous I/O, and allocation and freeing of main memory; it had no file system or other support for secondary storage.
The original version was written in MACRO-11, the assembly language for the PDP-11; it was later re-written at least three times in C: at BBN, at UCL, and at Proteon. The first and last versions were portable; the latter 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, and to support pseudo-terminals.
