Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. Today's Unix systems are split into various branches, developed over time by AT&T, as well as various commercial vendors and non-profit organizations.
The present owner of the trademark UNIX is The Open Group, an industry standards consortium. The rights to the UNIX source code, however, are being challenged in a 2004 federal lawsuit, in which Unix vendor SCO Group Inc. accused Novell of slander of title.
Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX" (others are called "UNIX system-like" or "Unix-like").
During the late 1970s and early 1980s, Unix's influence in academic circles led to large-scale adoption (particularly of the BSD variant, originating from the University of California, Berkeley) of Unix by commercial startups, the most notable of which is Sun Microsystems. Today, in addition to certified UNIX systems, Unix-like operating systems such as Linux and Mac OS X are commonly encountered.