Xenix was a Unix-like computer operating system derived from the UNIX system developed by Microsoft. It was later transformed by Santa Cruz Operation (SCO) into SCO UNIX.

History

Xenix was Microsoft's version of UNIX intended for use on microprocessors, but they called it Xenix because it could not license the "UNIX" name.

Microsoft purchased a license for UNIX 7th Edition from AT&T in 1979, and announced on August 25, 1980 that it would make it available for the 16-bit microcomputer market.

Xenix varied from its 7th Edition origins by incorporating elements from BSD, and soon possessed the most widely installed base of any Unix flavor due to the popularity of the inexpensive x86 processor, even though the port created for Tandy computers proved to be more robust.

Xenix was not sold directly to end users; Microsoft licensed it to computer manufacturers who then ported it to their systems. The first ports of Xenix were to the Zilog Z8001 16-bit processor. Altos shipped a version for their computers early in 1982, Tandy Corporation shipped one for their 68000-based systems in January 1983, and Santa Cruz Operation (SCO) released their port to the Intel 8086 processor in September 1983. At the time, Xenix was based on AT&T's UNIX System III.

Version 2.0 of Xenix was released in 1985 that was based on UNIX System V. An update numbered 2.1.1 added support for the Intel 80286 processor. Subsequent releases improved System V compatibility.

When Microsoft entered into an agreement with IBM to develop OS/2, it lost interest in promoting Xenix. In 1987 Microsoft transferred ownership of Xenix to SCO in an agreement that left Microsoft owning 25% of SCO.

In 1989, SCO ported Xenix to the 386 processor, a 32-bit chip. The Xenix 2.3.1 introduced support for i386, SCSI and TCP/IP.

Microsoft continued to use Xenix internally, submitting a patch to support functionality in UNIX to AT&T in 1987, which trickled down to the code base of both Xenix and SCO UNIX. Microsoft is said to have used Xenix on VAX minicomputers extensively within their company as late as 1992.

SCO branched Xenix into SCO UNIX in 1989. In the meantime, AT&T completed its merge of Xenix, BSD, SunOS and System V into System V Release 4 . SCO UNIX was still based on System V Release 3, but had most features of Release 4. The last version of Xenix itself was 2.3.4.