The Computers: Software: Operating Systems: (Unix Operating Systems )

All operating systems (OSs) in this section support POSIX standards fully. The main standard defining what constitutes a Unix OS is POSIX, an acronym for: Portable Operating System Interface for UniX. Much like TRON, POSIX is not a body of computer code that is compiled and run on some processor. Rather, it is a set of standards (IEEE 1003.1): interfaces, design guidelines, software design specifications, defining (for creating) the computer code that will become language interfaces between an OS kernel and its programs, to give compatibility when moving programs between compatible systems. POSIX is made mostly of features from BSD Unix and Unix System V. Much like Open Source software, all POSIX standards are copyrighted (by the Institute of Electrical and Electronics Engineers, Inc. Unix Operating Systems Software Computers.

Unix ( / ˈ j uː . n ɪ k s / ; trademarked as UNIX ) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, developed in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. (wikipedia)