Development of UNIX:
The original UNIX development was performed on a Digital PDP-7 minicomputer and later moved to a PDP-11 minicomputer, the forerunner of the VAX computer. Originally, the system was written in assembly language, but at the later stage the operating system was largely rewritten in C.
UNIX introduced many important OS concepts which have become a trend in OS design today, including the hierarchical file system, the shell concept, redirection, piping, and the use of simple commands that can be combined to perform powerful operations.
The authors Ken Thompson and Denis Ritchie of the OS also developed techniques for interprocess communication, and even provided for networked and distributed processing. UNIX earned a reputation for power and flexibility. Because it was written in C, it was also easy to port it that is to make it run on other computers.
As a result of these factors, UNIX became an important operating system for universities and was ultimately adopted, in many versions.
Another important innovation, some would say the most important development in making the computer accessible to nontechnical users, was the development of the concept of graphical user interfaces.