Unix is a multiuser, multitasking operating system that has historically been used for workstations and servers in science, engineering, research, and in the development and running of the Internet. Today, one can also find Unix systems in businesses of all sizes as well as in the home. Developed in the early 1970s at AT&T Bell Labs (now part of Alcatel-Lucent, SA), Unix was the first major OS written in a high-level language (C, which was also developed at Bell Labs). It was also the first major program written in C. The link between Unix and C is still visible today in the C-shell (csh) command-line interface that's used on many Unix systems.
Unix is highly portable and platform-independent, as it can run virtually anywhere one can find a C compiler. Other attractive features include its stability due to advanced memory protection, its ability to run multiple simultaneous processes due to preemptive multitasking, and its scalability in large environments. In addition, many of the networking components of Unix have become Internet standards. These include TCP/IP (Transport Control Protocol/Internet Protocol), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and TELNET (Network Terminal Protocol).
For most of its history, the user interface has been a terse and arcane, but fast and efficient, command line. In recent years, however, several advanced graphical user interfaces (GUI's) have been introduced.
Many "flavors" of Unix have evolved over the years, including BSD (Berkeley Standard Distribution), Xenix, Posix, Linux, HP-UX, and SunOS.
The name Unix (also written UNIX) is believed to be a pun on Multics (Multiplexed Information and Computing Service). The latter was a time-sharing operating system for mainframe computers that Unix co-inventor Ken Thompson developed in the late 1960s.