daemon

/daymn/ , /deemn/ , n. [from Maxwell's Demon, later incorrectly retronymed
as Disk And Execution MONitor ] A program that is not invoked explicitly,
but lies dormant waiting for some condition(s) to occur. The idea is that
the perpetrator of the condition need not be aware that a daemon is lurking
(though often a program will commit an action only because it knows that it
will implicitly invoke a daemon). For example, under ITS , writing a file on
the LPT spooler's directory would invoke the spooling daemon, which would
then print the file. The advantage is that programs wanting (in this
example) files printed need neither compete for access to nor understand any
idiosyncrasies of the LPT. They simply enter their implicit requests and let
the daemon decide what to do with them. Daemons are usually spawned
automatically by the system, and may either live forever or be regenerated
at intervals. Daemon and demon are often used interchangeably, but seem to
have distinct connotations. The term daemon was introduced to computing by
CTSS people (who pronounced it /deemon/ ) and used it to refer to what ITS
called a dragon ; the prototype was a program called DAEMON that
automatically made tape backups of the file system. Although the meaning and
the pronunciation have drifted, we think this glossary reflects current
(2003) usage.

