XENIX is directly based on UNIX Version 7. Its first version, 2.3, was released in 1980 by Microsoft for use on microcomputers (IBM PCs or clones).
XENIX 3.0, released in 1983, included new features from 4.1BSD and from AT&'s System III.
Finally, the latest version, XENIX 5.0 was released in 1985, and conforms to the System V Interface Definition.