Xenix

Xenix is a discontinued Unix operating system for various microcomputer platforms, licensed by Microsoft from AT&T Corporation. The first version was released in 1980, and Xenix was the most common Unix variant during the mid- to late-1980s. The Santa Cruz Operation (SCO) acquired exclusive rights to the software, and eventually replaced it with SCO UNIX, later known as OpenServer, with the final Xenix version released in 1991.

Bell Labs, the developer of Unix, was part of the regulated Bell System and could not sell Unix directly to most end users (academic and research institutions excepted); it could, however, sell it to software vendors who would then resell it to end users (or their own resellers), combined with their own added features. Microsoft, which expected that Unix would be its operating system of the future when personal computers became powerful enough, purchased a license for Version 7 Unix from AT&T in 1978, and announced on August 25, 1980, that it would make the software available for the 16-bit microcomputer market. Because Microsoft was not able to license the "Unix" name itself, the company gave it an original name.

While "MS-DOS will become the premier single-user operating system", said Microsoft cofounder Paul Allen, his company "hopes that Xenix will become the preferred choice for software production and exchange", it stated in 1981. MS-DOS was Microsoft's "single-user, single-tasking operating system", which can run from floppy disks. Xenix, Allen said, "really should be used with a hard disk". MS-DOS and Xenix are "part of a family ... with a clear migration path", he added, promising binary compatibility of Xenix-compiled C software with MS-DOS, and interoperability of Xenix-based file servers and MS-DOS application servers. The company advised customers who wanted multiuser or multitasking support to buy Xenix.

Microsoft expected that MS-DOS would become almost indistinguishable from single-user Xenix, or XEDOS, which would also run on the 68000, Z8000, and LSI-11; they would be upwardly compatible with Xenix, which Byte in 1983 described as "the multi-user MS-DOS of the future". Microsoft's Chris Larson described MS-DOS 2.0's Xenix compatibility as "the second most important feature". His company advertised DOS and Xenix together, describing MS-DOS 2.0 (its "single-user OS") as sharing features and system calls with Xenix ("the multi-user, multi-tasking, Unix-derived operating system"), and promising easy porting between them.

Microsoft called Xenix "a universal operating environment". It did not sell Xenix directly to end users, but licensed the software to OEMs. Microsoft received $500 for each single-user copy sold by companies such as IBM, Intel, Management Systems Development, Tandy, Altos Computer, SCO, and Siemens (SINIX) which then ported it to their own proprietary computer architectures.

In 1981, Microsoft said the first version of Xenix was "very close to the original Unix version 7 source" on the PDP-11, and later versions were to incorporate its own fixes and improvements. The company stated that it intended to port the operating system to the Zilog Z8000 series, Digital LSI-11, Intel 8086 and 80286, Motorola 68000, and possibly "numerous other processors", and provide Microsoft's "full line of system software products", including BASIC and other languages. The first port was for the Z8001 16-bit processor: the first customer ship was January 1981 for Central Data Corporation of Illinois, followed in March 1981 by Paradyne Corporation's Z8001 product. The first 8086 port was for the Altos Computer Systems' non-PC-compatible 8600-series computers (first customer ship date Q1 1982).

Intel sold complete computers with Xenix under their Intel System 86 brand (with specific models such as 86/330 or 86/380X); they also offered the individual boards that made these computers under their iSBC brand. This included processor boards like iSBC 86/12 and also MMU boards such as the iSBC 309. The first Intel Xenix systems shipped in July 1982. Tandy more than doubled the Xenix installed base when it made TRS-Xenix the default operating system for its TRS-80 Model 16 68000-based computer in early 1983, and was the largest Unix vendor in 1984. Seattle Computer Products also made (PC-incompatible) 8086 computers bundled with Xenix, like their Gazelle II, which used the S-100 bus and was available in late 1983 or early 1984. There was also a port for IBM System 9000.

SCO had initially worked on its own PDP-11 port of V7, called Dynix, but then struck an agreement with Microsoft for joint development and technology exchange on Xenix in 1982. Microsoft and SCO then further engaged Human Computing Resources Corporation (HCR) in Canada, and a software products group within Logica plc in the United Kingdom, as part of making further improvements to Xenix and porting Xenix to other platforms. In doing so, Microsoft gave HCR and Logica the rights to do Xenix ports and to license Xenix binary distributions in those territories.