In August 1969, Ken Thompson and Denis Ritchie of Bell Labs, dissatisfied with the size and complexity of the Multics OS, after one month of hard work, first working prototype of an operating system , created in assembly language for the PDP-7 minicomputer. Around the same time, the high-level programming language Bee was developed, which evolved into the C language a few years later.
In early 1970, Brian Kernighan, Douglas McIlroy, and Joe Ossana joined the project, with whom Unix was adapted for the PDP-11. In 1972, the developers abandoned the assembly language and partially rewrote the system in high-level B language, and over the next 2 years the system was gradually completely rewritten in C, after which the popularity of Unix in the university environment increased significantly.
Source: opennet.ru