Unix daemons got their name from an imaginary molecule sorter, not an acronym
Fernando Corbató's surviving reply settles a bit of computer folklore that keeps acquiring extra capital letters.
A background process acquired a backstory so elaborate that somebody eventually asked the person who had been there. Convenient! Computer history occasionally comes with a reply button.
Richard Steinberg, writing a trivia column for the Austin Chronicle, contacted Fernando Corbató about the origin of daemon. The question bundled several claims together: Project MAC, an IBM computer, tape backups and an expansion that made the word look suspiciously well behaved in capital letters.
Corbató accepted the approximate timing of his group’s use of the word. The expansion got a different reception. In the preserved correspondence, he called it “a new one on me.” That’s a fairly awkward performance review for an alleged original acronym.
He explained that the inspiration came from physics. Maxwell’s imaginary agent sorted molecules by speed and kept working in the background. His computing group borrowed that image for processes doing system chores. The tiny attendant in a thought experiment became the attendant inside the machine.
The archive also records confirmation from Project MAC colleague Jerome Saltzer. That matters because the explanation has more behind it than somebody noticing that two words happen to fit. People involved in the naming identified what they had in mind.
The questioner’s tape-backup detail deserves a little care. It appears in the incoming question; Corbató’s reply concentrates on the time frame and the name. Turning everything in the question into something he personally confirmed would give the correspondent quite a promotion.
The archive preserves the incoming question alongside the answer, which lets a reader see exactly what was challenged. That is especially helpful with technical folklore: a short quotation passed around alone can lose the distinction between an origin somebody proposed and the origin its participant actually remembered.
A name can survive perfectly well after its original reference becomes obscure. People can use a daemon without remembering nineteenth-century physics, just as they can save a file without owning the object on the save icon. Computers are full of little history lessons that nobody bothered to label.
But recovering this one changes the mental picture. The machine has a helper quietly sorting things, rather than a supernatural infestation requiring a support ticket. The chores are ordinary. The mythology is optional.
Future retellings can still invent more elaborate expansions. This exchange gives readers a wonderfully small way to check them: the person who helped choose the word explained the choice himself, without requiring a capital letter scavenger hunt.
The daemon has chores to do.