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Developer AT&T
OS family Unix
Working state Historic
Source model closed

UNIX System III (or System 3) is a discontinued version of the Unix operating system released by AT&T's Unix Support Group (USG).

AT&T announced System III in late 1981,[1] and it was first released outside of Bell Labs in 1982. UNIX System III was a mix of various AT&T Unixes: PWB/UNIX 2.0, CB UNIX 3.0, UNIX/TS 3.0.1 and UNIX/32V. System III supported the DEC PDP-11 and VAX computers.

The system was apparently called System III because it was considered the outside release of UNIX/TS 3.0.1 and CB UNIX 3 which were internally supported Bell Labs Unices; its manual refers to it as UNIX Release 3.0[2] and there were no Unix versions called System I or System II. There was no official release of UNIX/TS 4.0 (which would have been System IV) either,[3][4] so System III was succeeded by System V, based on UNIX/TS 5.0.

System III introduced new features such as named pipes, the uname system call and command, and the run queue. It also combined various improvements to Version 7 Unix by outside organizations. However, it did not include notable additions made in BSD such as the C shell (csh) and screen editing.

Third-party variants of System III include (early versions of) HP-UX, IRIX, IS/3, PC-UX, PNX, SINIX, Venix and Xenix.


  1. ^ Fiedler, Ryan (October 1983). "The Unix Tutorial / Part 3: Unix in the Microcomputer Marketplace". BYTE. p. 132. Retrieved 30 January 2015. 
  2. ^ T. A. Dolotta, S. B. Olsson and A. G. Petruccelli, eds. (June 1980). UNIX User's Manual, Release 3.0. Bell Telephone Laboratories. 
  3. ^ Dale Dejager (1984-01-16). "UNIX History". Newsgroupnet.unix. 
  4. ^ Tanenbaum, Andrew S. (2001). Modern Operating Systems (2nd ed.). Upper Saddle River, NJ: Prentice Hall. p. 675. ISBN 0-13-031358-0. Whatever happened to System IV is one of the great unsolved mysteries of computer science. 

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