multiuser computer operating system. UNIX is widely used for Internet servers, workstations, and mainframe computers.

UNIX was developed by AT&T Corporation (AT&T Corporation)'s Bell Laboratories in the late 1960s as a result of efforts to create a time-sharing computer system. In 1969 a team led by computer scientists Ken Thompson and Dennis Ritchie created the first version of UNIX on a PDP-7 minicomputer, which was chosen mainly because of Thompson's familiarity with the system from his hobby work on it. UNIX was quickly adapted for another computer, and the team ported (modified) it to the PDP-11 by late 1970. This would be the first of many ports of UNIX.

Thompson left Bell Laboratories for a while and taught a course on UNIX at the University of California at Berkeley in the mid-1970s. Students and professors there further enhanced UNIX, eventually creating a version of UNIX called Berkeley Software Distribution (BSD). Work at AT&T also continued, leading to the 1983 release of a new version of UNIX called System V. These versions were later joined by UNIX versions created by Sun Microsystems, Inc., and Silicon Graphics, Inc. (SGI), among other companies, and continued development kept UNIX on pace with improvements in computer technology. UNIX served as the inspiration for free open-source (open source) operating systems such as Linux and FreeBSD, and it is the basis for Apple Inc.'s Mac OS X.

The main features of UNIX—its portability (the ability to run on many different systems), multitasking and multiuser capabilities, and its extensive library of software—make it as relevant and useful today as it was in 1969.