The UNIX story begins in 1969, when a joint project between Bell Laboratories, General Electric, and the Massachusetts Institute of Technology was abandoned. Multics, the project in question, was an experimental operating system on the GE 635.
Ken Thompson and Dennis Ritchie, both from Bell Labs, had been exposed to the Multics project. They ported a game, called `Space Travel', from the GE 635 running Multics, onto a PDP-7. To help them do the porting, Thompson wrote a ``simple file system and some utilities for the PDP-7" [p. 3]RT:UNIX. This was the birth of UNIX, in 1970 (``UNIX" was meant to be a pun on ``Multics").
Late in 1970, a PDP-11/20 was purchased, and UNIX became an official Bell Labs project. The first UNIX edition ``was documented in a manual authored by Thompson and Ritchie dated November 1971" [p. 2]SR:UNIX. Most of the ideas found in today's UNIX systems were incorporated in this edition.
The second edition, 1972, incorporated the piping concept.
In 1973, UNIX was re-written in C, by Thompson and Ritchie. Note that Ritchie developed the C language (derived from the B language by Thompson) at approximately the same time.
UNIX was first distributed in May 1975 for a nominal fee. This was UNIX Version 6.
In 1979, a more portable version of UNIX (Version 7) was released for general use; from here, three major UNIX versions emerged: BSD (Berkeley System Distribution), XENIX, and AT&'s System V.