daemon
/day'mn/ or /dee'mn/ [from the mythological meaning,
later rationalized as the acronym `Disk And Execution MONitor'] n.
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 /dee'mon/) and
used it to refer to what ITS called a dragon. Although the
meaning and the pronunciation have drifted, we think this glossary
reflects current (1993) usage.
