Odd Comments and Strange Doings in Unix

A firsthand account from a Unix pioneer explaining the origins of two famous pieces of Unix lore: the cryptic error message 'values of β will give rise to dom!' found in mv.c of Sixth Edition Unix, and the notorious comment 'You are not expected to understand this' in the kernel's process-switching code. The author reveals the beta message originated from a typist accidentally printing a fragment of a patent application on a Model 37 Teletype in the early 1970s. The 'you are not expected to understand this' comment is clarified as a humble admission — the authors genuinely didn't understand the broken savu/retu process-exchange mechanism, which failed when porting to the Interdata due to differing compiler register-save conventions. Additional anecdotes cover an undocumented PDP-11 division routine bug and a hardware wiring error in the KS-11 memory mapping unit discovered via circuit drawings.

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