UNIX is a computer operating system. It was first developed in 1969 at Bell Labs. Ken Thompson, Dennis Ritchie, Douglas McIlroy, and others created it. They used assembly language to write it. In 1972, the Unix code was rewritten with the new C programming language. The Unix operating system is a multiuser and multiprocessing system. This means it can run several application programs at the same time, for more than one user at the same time. It also is able to operate well in a network of computers. Computer security is also important in Unix, because many people can have access to it, both by using a computer directly or over a network.