Around 1977 or so, I worked with MOS, a "mini" operating system for the PDP-11. I think it was originally developed at SRI, to support the BBN Packet Radio networking research. It was written in assembly language, supplied in source form. Tasks were defined statically, at assembly time. There was a single-user TCP and Telnet. Someone else did a multplexer, to allow multiple tasks to set up TCP instances. It was a VERY simple thing, but it worked.

I've been trying to track down it down for a while, to no avail. It looks as though it has disappeared completely.

No, this isn't a "Fuzzball", although they appear to have similar purposes.

Does anyone have any pointers?

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    Oh yes, "Mathis'" Operating System. I have encountered MOS many times in my research, along with Fuzzball, ELF, ANTS, RATS, and others. I understand MOS was used heavily at MIT for network routing. Internet pioneer J. Noel Chiappa has written about it here: gunkies.org/wiki/MOS_operating_system Jan 19, 2022 at 8:06
  • @LarsBrinkhoff: That's definitely it! Any idea where I can find source copies? Jan 19, 2022 at 12:49
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    @JohnRStrohm, I asked Chiappa about it and only minutes ago he put some files online. They are now linked from the gunkies page. Jan 19, 2022 at 14:47

1 Answer 1


I made this, but most of the credit should go to J. Noel Chiappa: https://github.com/pdp11/mos-operating-system

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