1965–1969

In 1965, Bell Labs joined with MIT and General Electric in a cooperative development of Multics, a multiuser, interactive operating system running on a GE 645 mainframe computer. However, unhappy with the progress in the development of a system that was experiencing many delays and high costs, Bell Labs dropped out of the development of Multics in 1969.

In 1969, Ken Thompson, exposed to Multics at Bell Labs, met up with Dennis Ritchie, who provided a Digital Equipment Corporation PDP-7 minicomputer to continue the development of an operating system capable of supporting a team of programmers in a research environment. After they created a prototype, Thompson returned to Bell Labs to propose the use of this new operating system as a document-preparation tool in the Bell Labs patent department. The new operating system was named UNIX to distinguish it from the complexity of Multics. Efforts to develop UNIX continued, and UNIX became operational at Bell Labs in 1971.

The first version of UNIX was written in assembly language on a PDP-11/20. It included the file system, fork, roff, and ed. It was used as a text-processing tool for the preparation of patents.