Trademark An operating system that originated in Bell Laboratories in 1969. The system was initially written to run on Digital Equipment’s PDP11 minicomputer, and was primarily intended to provide a working environment for a group of users cooperating on a small number of related projects; the group thus had considerable shared interests over and above the fact that they all used the same computer system. In the intervening years UNIX has become very popular and is now the effective standard for workstations and mid-range systems.

UNIX provides a consistent approach to multitasking, with built-in operations for the creation, synchronization, and termination of processes either from the system environment or from within an existing process. This allows the extension and customization of the UNIX command set. There is also a consistent file-management system that provides a structured means of directory control and of file naming, with the ability to control access to files, including mechanisms for shared access. The output from any process can be directed to a file, or can itself serve as the input to some other process, with the operating system ensuring that the producing and consuming process remain correctly synchronized.

UNIX has been implemented by a wide range of workers and on a wide range of hardware platforms. Versions have been written by individual workers through to large software houses and major hardware manufacturers, for computer systems from desktop computers through to enterprise servers. As an almost inevitable consequence there has been a bewildering number of restrictions and/or extensions to the facilities offered by the system, as well as differing implementations of what are apparently the same features. There have been repeated efforts at standardization, and several versions have been defined. The current position (2019) is that only those systems that comply with The Open Group’s Single UNIX Specification may call themselves ‘UNIX.’

http://www.unix.org/ The Open Group’s UNIX page