System 4 or System IV may refer to: *

Acorn System 4 The Acorn Eurocard systems were a series of modular microcomputer systems based on rack-mounted Eurocards developed by Acorn Computers from 1979 to 1982, aimed primarily at industrial and laboratory use, but also home enthusiasts. The experience ...

, the early minicomputer * The fourth release of

Classic Mac OS Mac OS (originally System Software; retronym: Classic Mac OS) is the series of operating systems developed for the Macintosh family of personal computers by Apple Computer from 1984 to 2001, starting with System 1 and ending with Mac OS 9. The ...

* International Computers Limited#English Electric LEO Marconi (EELM), also known as ICL System 4 * Not-released Unix system between UNIX System III and

UNIX System V Unix System V (pronounced: "System Five") is one of the first commercial versions of the Unix operating system. It was originally developed by AT&T and first released in 1983. Four major versions of System V were released, numbered 1, 2, 3, an ...

* STS-4 (Space Transportation System-4), the Space Shuttle mission

See also