UNIX development was started in 1969 at Bell Laboratories in New Jersey. Bell Laboratories was (1964–1968) involved on the development of a multi-user, time-sharing operating system called Multics (Multiplexed Information and Computing System). Multics was a failure. In early 1969, Bell Labs withdrew from the Multics project.
Bell Labs researchers who had worked on Multics (Ken Thompson, Dennis Ritchie, Douglas McIlroy, Joseph Ossanna, and others) still wanted to develop an operating system for their own and Bell Labs’ programming, job control, and resource usage needs. When Multics was withdrawn Ken Thompson and Dennis Ritchie needed to rewrite an operating system in order to play space travel on another smaller machine (a DEC PDP-7 [Programmed Data Processor 4K memory for user programs). The result was a system called UNICS (UNiplexed Information and Computing Service) which was an 'emasculated Multics'.
The first version of Unix was written in the low-level PDP-7 assembler language. Later, a language called TMG was developed for the PDP-7 by R. M. McClure. Using TMG to develop a FORTRAN compiler, Ken Thompson instead ended up developing a compiler for a new high-level language he called B, based on the earlier BCPL language developed by Martin Richard. When the PDP-11 computer arrived at Bell Labs, Dennis Ritchie built on B to create a new language called C. Unix components were later rewritten in C, and finally with the kernel itself in 1973.
Unix V6, released in 1975 became very popular. Unix V6 was free and was distributed with its source code.
In 1983, AT&T released Unix System V which was a commercial version.
Meanwhile, the University of California at Berkeley started the development of its own version of Unix. Berkeley was also involved in the inclusion of Transmission Control Protocol/Internet Protocol
(TCP/IP) networking protocol.
The following were the major mile stones in UNIX hostory early 1980's
• AT&T was developing its System V Unix.
• Berkeley took initiative on its own Unix BSD (Berkeley Software Distribution) Unix.
• Sun Microsystems developed its own BSD-based Unix called SunOS and later was renamed to Sun Solaris.
• Microsoft and the Santa Cruz operation (SCO) were involved in another version of UNIX called XENIX.
• Hewlett-Packard developed HP-UX for its workstations.
• DEC released ULTRIX.
• In 1986, IBM developed AIX (Advanced Interactive eXecutive).