A/UX is Apple Computer’s implementation of the Unix operating system for some of its Macintosh computers. A/UX requires a 68k-based Macintosh with an FPU and a paged memory management unit (PMMU), and various versions run on the Macintosh II, SE/30, Quadra and Centris series of machines. A/UX was first released in 1988, with the final version of 3.1.1 released in 1995.
Described by InfoWorld as "an open systems solution with the Macintosh at its heart", the operating system is based on UNIX System V Release 2.2. It includes some additional features from System V Releases 3 and 4 and BSD versions 4.2 and 4.3. It is POSIX and System V Interface Definition (SVID) compliant and includes TCP/IP networking from version 2 onward. Having a Unix-compatible, POSIX-compliant operating system made it possible for Apple to bid for large contracts to supply computers to U.S. federal government institutes.