1. Not operating. "The up escalator is down" is considered a
humorous thing to say, and "The elevator is down" always
means "The elevator isn't working" and never refers to what
floor the elevator is on. With respect to computers, this
term has passed into the mainstream; the extension to other
kinds of machine is still hackish.
2. "go down" To stop functioning; usually said of the
hates to hear from the operator is "System going down in 5
minutes".
3. "take down", "bring down" To deactivate purposely, usually
for repair work or
PM. "I'm taking the system down to work
on that bug in the tape drive." Occasionally one hears the
word "down" by itself used as a verb in this sense.
(1994-12-07)