Xenix

Xenix was a version of the Unix operating system that Microsoft published from 1980 to 1987, after which the Santa Cruz Operation, SCO, took over its development until 1991. Microsoft licensed the Unix System V source code from AT&T in the late 1970s and ported it to run on 16 bit Intel x86 processors, building Xenix as a multiuser, multitasking alternative to its own MS-DOS. Microsoft scaled back its own development after AT&T began marketing Unix directly, but SCO continued to improve the system, and Xenix was probably the most widely installed version of Unix during the second half of the 1980s; SCO's 1987 port to the 386 processor made Xenix System V/386 the first 32 bit operating system available for the x86 architecture. The final release, System V Release 2.3.4, came out in 1991, after which SCO UNIX succeeded it. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/