page_title: Xenix
section_title: History
hierarchical_section_title: Xenix / History
caption_attribution_description: Digitally enhanced version of Ms_xenix.jpg
context_page_description: Xenix is a discontinued version of the Unix operating system for various microcomputer platforms, licensed by Microsoft from AT&T Corporation in the late 1970s. The Santa Cruz Operation later acquired exclusive rights to the software, and eventually replaced it with SCO UNIX.
  In the mid-to-late 1980s, Xenix was the most common Unix variant, measured according to the number of machines on which it was installed.
  Microsoft chairman Bill Gates said at Unix Expo in 1996 that, for a long time, Microsoft had the highest-volume AT&T Unix license.
context_section_description: 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 license 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 it 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.
  Microsoft called XENIX "a universal operating environment". It did not sell XENIX directly to end users, but licensed the software to OEMs such as IBM, Intel, Management Systems Development, Tandy, Altos, SCO, and Siemens (SINIX) who 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.
  In 1984, a port to the 68000-based Apple Lisa 2 was jointly developed by SCO and Microsoft and it was the first shrink-wrapped binary product sold by SCO. The Multiplan spreadsheet was released for it.
  In its 1983 OEM directory, Microsoft said the difficulty in porting to the various 8086 and Z8000-based machines had been the lack of a standardized memory management unit and protection facilities. Hardware manufacturers compensated by designing their own hardware, but the ensuing complexity made it "extremely difficult if not impossible for the very small manufacturer to develop a computer capable of supporting a system such as XENIX from scratch," and "the XENIX kernel must be custom-tailored to each new hardware environment."
  A generally available port to the unmapped Intel 8086/8088 architecture was done by The Santa Cruz Operation around 1983. SCO XENIX for the PC XT shipped sometime in 1984 and contained 
caption: IBM/Microsoft XENIX 1.00 on 5¼-inch floppy disk
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