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/tops-ten/ DEC's proprietary OS for the fabled PDP-10 machines, long a favourite of hackers but now effectively extinct. A fountain of hacker folklore. See also ITS, TOPS-20, TWENEX, VMS, operating system. TOPS-10 was sometimes called BOTS-10 (from "bottoms-ten") as a comment on the inappropriateness of describing it as the top of anything.