demon

The unusual computing term demon (sometimes spelled daemon) refers to a process (program) that runs in the background, checking for and responding to certain events. The utility of this concept is that it allows for automation of information processing without requiring that an operator initiate or manage the process.

For example, a print spooler demon looks for jobs that are queued for printing, and deals with the negotiations nec-essary to maintain the flow of data to that device. Another demon (called chron in UNIX systems) reads a file describ-ing processes that are designated to run at particular dates or times. For example, it may launch a backup utility every morning at 1:00 a.m. E-mail also depends on the periodic operation of “mailer demons.”

While the term demon originated in the UNIX culture, similar facilities exist in many operating systems. Even in the relatively primitive MS-DOS for IBM personal comput-ers of the 1980s, the ability to load and retain small utility programs that could share the main memory with the cur-rently running application allowed for a sort of demon that could spool output or await a special keypress. Microsoft Windows systems have many demon-like operating system components that can be glimpsed by pressing the Ctrl-Alt-Delete key combination.

The sense of autonomy implied in the term demon is in some ways similar to that found in bots or software agents that can automatically retrieve information on the Internet, or in the Web crawler, which relentlessly pursues, records, and indexes Web links for search engines. (See software agent and search engine.)