Xenix

Xenix is a Unixoperating system that was published by Microsoft from 1980 to 1987, and by the Santa Cruz Operation (SCO) from 1987 to 1991. Xenix is based on the operating system UNIX System V, which Microsoft licensed from AT&T Corporation in the late 1970s. UNIX System V ran on the PDP-11minicomputer. Microsoft ported the source code so the operating system could run on certain 16-bit processors in the Intel x86 family. After some additional modifications, Microsoft published Xenix in 1980.

One consequence of the breakup of the Bell System in the late 1970s was that AT&T started marketing UNIX themselves in the early 1980s. Not wishing to compete with AT&T in the UNIX market, Microsoft abandoned development of Xenix shortly thereafter, but continued to market the product. In 1987, SCO (a company in which Microsoft had a partial stake) made a deal with Microsoft to acquire the exclusive rights to Xenix. At that time, Xenix was the most widely deployed commercial UNIX operating system.

SCO resumed development of Xenix, and continued to release new versions of it until 1991. In the interim, they developed their own System V variant for Intel i386 processors, SCO UNIX, and released it in 1989.