<P> The pre-history of Unix dates back to the mid-1960s when the Massachusetts Institute of Technology, Bell Labs, and General Electric were developing an innovative time - sharing operating system called Multics for the GE - 645 mainframe . Multics introduced many innovations, but had many problems . Frustrated by the size and complexity of Multics but not by the aims, Bell Labs slowly pulled out of the project . Their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M.D. McIlroy, and J.F. Ossanna, decided to redo the work on a much smaller scale . </P> <P> The name Unics (Uniplexed Information and Computing Service, pronounced as "eunuchs"), a pun on Multics (Multiplexed Information and Computer Services), was initially suggested for the project in 1970: the new operating system was an emasculated Multics . Peter H. Salus credits Peter Neumann with the pun, while Brian Kernighan claims the coining for himself, and adds that "no one can remember" who came up with the final spelling Unix . Dennis Ritchie also credits Kernighan . </P> <P> In 1972, Unix was rewritten in the C programming language . The migration from assembly to the higher - level language C resulted in much more portable software, requiring only a relatively small amount of machine - dependent code to be replaced when porting Unix to other computing platforms . Bell Labs produced several versions of Unix that are collectively referred to as Research Unix . In 1975, the first source license for UNIX was sold to Donald B. Gillies at the University of Illinois Department of Computer Science . UIUC graduate student Greg Chesson (who had worked on the UNIX kernel at Bell Labs) was instrumental in negotiating the terms of this license . </P> <P> During the late 1970s and early 1980s, the influence of Unix in academic circles led to large - scale adoption of Unix (BSD and System V) by commercial startups, including Sequent, HP - UX, Solaris, AIX, and Xenix . In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4 (SVR4), which was subsequently adopted by many commercial Unix vendors . </P>

The first unix operating system was written in which language