Editing Xenix (section)

==History==
[[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,{{r|letwin19950817}} purchased a license for [[Version 7 Unix]] from AT&T in 1978,<ref>{{cite book |author-first=Steve D. |author-last=Pate |title=Unix Internals: A Practical Approach |date=1996 |publisher=[[Addison Wesley Professional]] |isbn=978-0-201-87721-2 |url=https://archive.org/details/unixinternalspra0000pate |url-access=registration}} p. 9 "Microsoft licensed Seventh Edition Unix from AT&T in 1978 to produce the Xenix operating system initially for the PDP-11."</ref> and announced on August 25, 1980, that it would make the software available for the [[16-bit]] microcomputer market.<ref>{{Cite web|url=http://channel9.msdn.com/Series/History/The-History-of-Microsoft-1980|title=The History of Microsoft - 1980}}</ref> Because Microsoft was not able to license the "Unix" name itself,<ref>{{cite web |url=http://www.computerhope.com/unix/xenix.htm |title=Xenix variant information |date=February 26, 2010 |quote=In the late 1970s Microsoft licensed Unix source code from AT&T, which at the time was not licensing the name Unix. |url-status=dead |archive-url=https://web.archive.org/web/20131219145551/http://www.computerhope.com/unix/xenix.htm |archive-date=December 19, 2013}}</ref> the company gave it an original name.

While "[[MS-DOS]] will become the premier single-user operating system", said Microsoft cofounder [[Paul Allen]],{{r|allen198206}} his company "hopes that Xenix will become the preferred choice for software production and exchange", it stated in 1981.<ref name="greenberg198106">{{Cite magazine |author-last=Greenberg |author-first=Robert B. |date=June 1981 |title=The Unix Operating System and the Xenix Standard Operating Environment |url=https://archive.org/stream/byte-magazine-1981-06/1981_06_BYTE_06-06_Operating_Systems#page/n249/mode/2up |magazine=[[Byte (magazine)|Byte]] |pages=248–264}}</ref> MS-DOS was Microsoft's "single-user, single-tasking operating system",<ref name="byte198207">{{cite news |url=https://archive.org/stream/byte-magazine-1982-07/1982_07_BYTE_07-07_Computers_in_the_Arts_and_Sciences#page/n321/mode/2up |title=Upward Migration / Part 2: A Comparison of CP/M-86 and MS-DOS |newspaper=[[BYTE]] |date=July 1982 |access-date=23 March 2016 |author-last1=Taylor |author-first1=Roger |author-last2=Lemmons |author-first2=Phil |pages=330}}</ref> 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 server]]s and MS-DOS [[application server]]s.<ref name="allen198206">{{Cite magazine |last=Allen |first=Paul |date=June–July 1982 |title=Future Plans for MS-DOS or The Bridge to XENIX |url=https://archive.org/details/PC-Mag-1982-06/page/n161/mode/2up?view=theater |access-date=2025-05-13 |magazine=PC Magazine |pages=161–162 |volume=1 |issue=3}}</ref> The company advised customers who wanted [[multiuser]] or [[Computer multitasking|multitasking]] support to buy Xenix.<ref name="byte198207"/><ref name="swaine19820823">{{cite news |url=https://books.google.com/books?id=VDAEAAAAMBAJ&pg=PA24 |title=MS-DOS: examining IBM PC's disk-operating system |newspaper=[[InfoWorld]] |date=August 23, 1982 |access-date=January 29, 2015 |author-last=Swaine |author-first=Michael |author-link=Michael Swaine (technical author) |pages=24}}</ref>

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 [[upward compatible|upwardly compatible]] with Xenix, which ''[[Byte (magazine)|Byte]]'' in 1983 described as "the multi-user MS-DOS of the future".<ref name="morgan198201">{{cite news |url=https://archive.org/stream/byte-magazine-1982-01/1982_01_BYTE_07-01_The_IBM_Personal_Computer#page/n7/mode/2up |title=Of IBM, Operating Systems, and Rosetta Stones |newspaper=[[Byte (magazine)|Byte]] |date=January 1982 |access-date=October 19, 2013 |author-last=Morgan |author-first=Chris |page=6}}</ref><ref name="fiedler198310">{{cite news |url=https://archive.org/stream/byte-magazine-1983-10/1983_10_BYTE_08-10_UNIX#page/n133/mode/2up |title=The Unix Tutorial / Part 3: Unix in the Microcomputer Marketplace |newspaper=[[BYTE]] |date=October 1983 |access-date=January 30, 2015 |author-last=Fiedler |author-first=Ryan |pages=132}}</ref> Microsoft's Chris Larson described MS-DOS 2.0's Xenix compatibility as "the second most important feature".<ref name="larson198311">{{cite news |url=https://archive.org/stream/byte-magazine-1983-11/1983_11_BYTE_08-11_Inside_the_IBM_PC#page/n291/mode/2up |title=MS-DOS 2.0: An Enhanced 16-Bit Operating System |newspaper=[[BYTE]] |date=November 1983 |access-date=19 March 2016 |author-last=Larson |author-first=Chris |pages=285}}</ref> His company advertised DOS and Xenix together, describing MS-DOS 2.0 (its "single-user OS") as sharing features and [[system call]]s with Xenix ("the multi-user, multi-tasking, Unix-derived operating system"), and promising easy porting between them.<ref name="iw19830627">{{cite news |url=https://books.google.com/books?id=yy8EAAAAMBAJ&pg=PA44 |title=Before you bet your business software on an OS, look who's betting on MS-DOS and Xenix. |newspaper=[[InfoWorld]] |date= June 27, 1983 |access-date= January 31, 2015 |pages=44 |type=advertisement}}</ref>

Microsoft called Xenix "a universal operating environment".{{r|greenberg198106}} It did not sell Xenix directly to end users, but licensed the software to [[Original equipment manufacturer|OEMs]]. Microsoft received $500 for each single-user copy<ref name="libes198012">{{Cite magazine |last=Libes |first=Sol |date=December 1980 |title=Bytelines |url=https://archive.org/details/byte-magazine-1980-12/page/n215/mode/1up?view=theater |magazine=BYTE |pages=214–218 |volume=5 |issue=12}}</ref> sold by companies such as IBM,<ref name="ibm">{{cite journal |title=Expanded personal computing power and capability |author-first1=Philip A. |author-last1=Korn |author-first2=John P. |author-last2=McAdaragh |author-first3=Clovis L. |author-last3=Tondo |date=1985 |journal=[[IBM Systems Journal]] |volume=24 |issue=1 |doi=10.1147/sj.241.0026 |pages=26–36}}</ref> Intel,<ref name="intel">{{cite book |title=Overview of the Xenix 286 Operating System |publisher=[[Intel Corporation]] |date=November 1984 |url=http://bitsavers.trailing-edge.com/pdf/intel/system3xx/xenix-286/174385-001_Overview_of_the_XENIX_286_Operating_System_Nov84.pdf |quote=Xenix 286 is Intel's value-added version of the Xenix operating system released by Microsoft Corporation.}}</ref> Management Systems Development,<ref name="byte198110">{{cite news |url=https://archive.org/stream/byte-magazine-1981-10/1981_10_BYTE_06-10_Local_Networks#page/n379/mode/2up |title=Available Today |newspaper=[[BYTE]] |date=October 1981 |access-date=16 March 2016 |pages=380 |type=advertisement}}</ref> [[Tandy Corporation|Tandy]], [[Altos Computer Systems|Altos Computer]], SCO, and Siemens ([[SINIX]]) which then [[porting|ported]] it to their own proprietary [[computer architecture]]s.

[[File:Ms xenix.png|thumb|250px|right|IBM/Microsoft Xenix 1.00 on 5¼-inch [[floppy disk]]]]
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 [[Microsoft BASIC|BASIC]] and other languages.{{r|greenberg198106}} The first port was for the Z8001 16-bit processor: the first customer ship was January 1981 for Central Data Corporation of Illinois,<ref name="dir83"/>{{rp|4}} followed in March 1981 by Paradyne Corporation's [[Z8001]] product.<ref name="dir83"/>{{rp|14}}
The first 8086 port was for the [[Altos Computer Systems]]' non-PC-compatible 8600-series computers (first customer ship date Q1 1982).<ref group="note">The Altos 8086 machines had a custom MMU, which used 4K pages.</ref><ref name="dir83"/>{{rp|3}}<ref>{{cite journal |title=Altos Unveils 16-Bit Micros With Unix, 1M-Byte Memory |journal = Computerworld: The Newsweekly of Information Systems Management|url=https://books.google.com/books?id=94T9BTjdzT0C&pg=RA1-PA17 |date=November 23, 1981 |publisher=[[Computerworld]] |pages=49–50 |issn=0010-4841}}</ref><ref>{{cite journal |author-first=John |author-last=Halamka |title=Review: Altos 586 |url=https://books.google.com/books?id=0C8EAAAAMBAJ&pg=PA89 |date=7 November 1983 |journal=[[InfoWorld]] |page=89 |issn=0199-6649}}</ref><ref>{{cite journal |title=Computerworld |journal = Computerworld: The Newsweekly of Information Systems Management|url=https://books.google.com/books?id=3UuWcPxTGDIC&pg=PT77 |date=October 26, 1987 |publisher=[[IDG Enterprise]] |pages=77– |issn=0010-4841}}</ref>

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.<ref>{{cite web |url=http://bitsavers.informatik.uni-stuttgart.de/pdf/intel/system3xx/172758-001_Introduction_to_the_System_86_330_and_380_Systems_Mar83.pdf |title=Introduction to the System 86/360 and System 86/330A Microcomputer Systems |author=<!--Not stated--> |date=1983 |website=bitsavers |publisher=Intel |access-date=November 30, 2022}}</ref> 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.<ref name="dir83"/>{{rp|9}}<ref group="note">Intel also offered their own [[iRMX]] operating system as an alternative for these.</ref> 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,<ref name="chin19830207">{{cite news |url=https://books.google.com/books?id=_y8EAAAAMBAJ&pg=PA3 |title=Radio Shack goes to Microsoft's Xenix for Model 16 micros |newspaper=[[InfoWorld]] |date=February 7, 1983 |access-date=January 31, 2015 |author-last=Chin |author-first=Kathy |pages=3}}</ref> and was the largest Unix vendor in 1984.<ref name="bartimo19850311">{{cite news |url=https://books.google.com/books?id=5C4EAAAAMBAJ&pg=PA28 |title=Tandy Revamps Product Line |newspaper=[[InfoWorld]] |date=March 11, 1985 |access-date=January 21, 2015 |author-last=Bartimo |author-first=Jim |pages=28–29}}</ref> [[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.<ref name="dir83"/>{{rp|17}}<ref>{{Citation |title=Gazelle II 16-bit Micro-Computer |url=http://bitsavers.trailing-edge.com/pdf/seattleComputer/brochures/Gazelle_II.pdf |year=1983 |archive-url=https://web.archive.org/web/20220811094327/http://bitsavers.trailing-edge.com/pdf/seattleComputer/brochures/Gazelle_II.pdf |publisher=Seattle Computer Products, Inc. |archive-date=11 Aug 2022 |url-status=live}}</ref> There was also a port for [[IBM System 9000]].<ref>BYTE Guide to the IBM PC, fall 1984, p.61</ref>

SCO had initially worked on its own PDP-11 port of V7, called Dynix,<ref group="note">Unrelated to the later [[Dynix]] from [[Sequent Computer Systems]]</ref> but then struck an agreement with Microsoft for joint development and technology exchange on Xenix in 1982.<ref name="pate-p9">{{harvnb|Pate|1996|page=9}} "The Santa Cruz Operation (SCO) was formed in 1979 by Larry and Doug Michels as a technical management consulting business. [...] SCO then changed its focus from consulting to the custom porting of Unix system software and applications. The first version of Unix which SCO developed and sold was called Dynix, a name subsequently used by Sequent. The operating system was based on Seventh Edition Unix and ran on the PDP-11. [...] In 1982, a joint development and technology exchange agreement was reached between SCO and Microsoft bringing together engineers from SCO and Microsoft to further enhance the Xenix operating system which was increasing in popularity. Microsoft and SCO worked together with Logica in the UK and HCR in Canada, producing enhancements to Xenix and porting Xenix to other platforms."</ref> 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.<ref name="pate-p9"/> In doing so, Microsoft gave HCR and Logica the rights to do Xenix ports and to license Xenix binary distributions in those territories.<ref name="doug-video">{{cite news | url=https://www.santacruztechbeat.com/2016/04/21/watch-doug-michels-sco/ | title=Watch: A look-back conversation with Doug Michels, co-founder of SCO | author-first=Sara | author-last=Isenberg | newspaper=Santa Cruz Tech Beat | date=April 21, 2016}} See around 10:45 mark of interview video.</ref>

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.<ref>{{harvnb|Pate|1996|page=10}} "In 1984 a port of Xenix was made to the Apple Lisa by SCO and Microsoft, and was subsequently sold successfully by SCO as their first binary product, showing the success of the shrink-wrapped market. A port was also made to the Tandy model 16B."</ref> The [[Multiplan]] spreadsheet was released for it.<ref>{{cite AV media |title=Photograph of Lisa Xenix Multiplan diskette |medium=Digital photography |language=en |url=https://i.postimg.cc/VLbyqzt9/xenix.png |access-date=24 September 2019 |format=JPEG |publisher=Postimg.com}}</ref>

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".<ref name="dir83">{{Cite book |url=https://www.osarchive.org/os/xenix/microsoft/Documentation/Microsoft_XENIX_OEM_Directory.pdf |title=Microsoft XENIX Operating System OEM Directory |publisher=Microsoft |publication-date=1983-05-01 |id=OEM0091B |access-date=2025-04-25}}</ref>{{rp|Introduction}}

A generally available port to the unmapped [[x86|Intel 8086/8088 architecture]] was done by The Santa Cruz Operation around 1983.<ref>{{cite conference |author-first1=John Bruno |author-last1=Hare |author-first2=Thomas Dean |author-last2=Thomas |title=Porting Xenix to the Unmapped 8086 |book-title=Proceedings of the USENIX Winter Conference |publisher=USENIX Association |date=1984 |location=Washington, D.C. }}</ref><ref>{{cite web |title=SCO Company History |publisher=Operating System Documentation Project |url=http://www.operating-system.org/betriebssystem/_english/fa-sco.htm |access-date=May 14, 2008}}</ref><ref>{{cite web |author-last=Barger |author-first=Jorn |author-link=Jorn Barger |title=Timeline of GNU/Linux and Unix |url=http://laurel.datsi.fi.upm.es/~ssoo/IG/download/timeline.html |access-date=May 14, 2008}}</ref> SCO Xenix for the PC XT shipped sometime in 1984 and contained some enhancement from [[4.2BSD]]; it also supported the [[Micnet]] local area networking.<ref>{{harvnb|Pate|1996|page=10}} "In 1983 the PC [XT] emerged. SCO started porting to the 8088 but concentrated on the 8086, producing a release of SCO Xenix in 1984 which ran in 640 Kbytes with a 10 Mbyte hard disk. The release could support three or more users simultaneously, had multiscreen (virtual console) facilities, [[Micnet]] local area networking and enhancements added from 4.2BSD."</ref>

While Unix was still rare in companies during the second half of the 1980s,<ref name="kelleher">{{cite news |date=February 3, 1986 |title=Corporate Unix: A system struggles to earn its stripes |url=https://books.google.com/books?id=UE1HODexHKoC&pg=PA44 |newspaper=[[Computerworld]] |page=44 |author-first=Joanne |author-last=Kelleher}}</ref> Xenix was probably the most commonly installed Unix.<ref>{{cite book |author-last1=Leffler |author-first1=Samuel J. |url=https://archive.org/details/designimplementa0000unse/page/7 |title=The Design and Implementation of the 4.3BSD UNIX Operating System |author-last2=McKusick |author-first2=Marshall Kirk |author-link2=Marshall Kirk McKusick |author-last3=Karels |author-first3=Michael J. |author-link3=Michael J. Karels |author-last4=Quarterman |author-first4=John S. |date=October 1989 |publisher=[[Addison-Wesley]] |isbn=0-201-06196-1 |page=[https://archive.org/details/designimplementa0000unse/page/7 7] |url-access=registration}}</ref> The 286 version of Xenix used the integrated MMU present on this chip, by running in [[Protected mode#The 286|286 protected mode]].<ref>[http://www.tenox.net/docs/microsoft_xenix_30_286_press_release.pdf Microsoft Xenix 3.0 ready for 286] {{webarchive |url=https://web.archive.org/web/20140107072346/http://www.tenox.net/docs/microsoft_xenix_30_286_press_release.pdf |date=January 7, 2014}}</ref> The 286 Xenix was accompanied by new hardware from Xenix OEMs. For example, the [[Sperry Corporation|Sperry]] PC/IT, an [[IBM Personal Computer/AT|IBM PC AT]] clone, was advertised as capable of supporting eight simultaneous [[dumb terminal]] users under this version.

While Xenix 2.0 was still based on Version 7 Unix,<ref>{{cite book |first=Ellie |last=Cutler |display-authors=etal |title=SCO Unix in a Nutshell |url=https://archive.org/details/scounixinnutshel00elli |url-access=registration |date=1994 |publisher=[[O'Reilly Media, Inc.]] |isbn=978-1-56592-037-8 |pages=[https://archive.org/details/scounixinnutshel00elli/page/312 312]–}}</ref> version 3.0 was upgraded to a [[Unix System III]] code base,<ref name="dir83"/>{{rp|9}}<ref name="Frisch2002">{{cite book |author-first=Æleen |author-last=Frisch |title=Essential System Administration: Tools and Techniques for Linux and Unix Administration |url=https://archive.org/details/essentialsystema00fris_0 |url-access=registration |date=2002 |publisher=[[O'Reilly Media, Inc.]] |isbn=978-0-596-55049-3 |page=xiii}}</ref><ref name="KentWilliams1990">{{cite book |author-first1=Allen |author-last1=Kent |author-link1=Allen Kent |author-first2=James G. |author-last2=Williams |title=Encyclopedia of Computer Science and Technology |volume=22 - Supplement 7 |chapter=Artificial Intelligence to Vector SPate Model in Information Retrieval |chapter-url=https://books.google.com/books?id=L7NOABDqaMcC&pg=PA404 |date=May 15, 1990 |publisher=[[CRC Press]] |isbn=978-0-8247-2272-2 |pages=404–}}</ref> a 1984 Intel manual for Xenix 286 noted that the Xenix kernel had about 10,000 lines at this time.<ref name="intel"/>{{rp|1–7}} It was followed by a [[Unix System V|System V R2]] codebase in Xenix 5.0 (a.k.a. Xenix System V).<ref name="Lapin1987">{{cite book |author-first=Juraj E. |author-last=Lapin |title=Portable C and Unix System Programming |date=1987 |publisher=[[Pearson Education]] |isbn=978-0-13-686494-3 |page=106 |quote=The Xenix 2.3 version generally resembles V7's [ABI]; the Xenix 3.0 version resembles SIII's, and the Xenix 5.0 version resembles SV2's.}}</ref>

=== Transfer of ownership to SCO ===
After the [[breakup of the Bell System]] in 1984, AT&T started selling System V.<ref name="shea19840220">{{cite news |url=https://books.google.com/books?id=hS4EAAAAMBAJ&pg=PA43 |title=New developments may decide battle over Unix |newspaper=[[InfoWorld]] |date=1984-02-20 |access-date=25 February 2016 |author-last=Shea |author-first=Tom |pages=43–45}}</ref> Microsoft, believing that it could not compete with Unix's developer, decided to abandon Xenix. The decision was not immediately transparent, which led to the term [[vaporware]].<ref name="NYT">{{cite journal |ref=refFlynn |author-first=Laurie |author-last=Flynn |date=24 April 1995 |title=The Executive Computer |journal=[[The New York Times]] |issn=0362-4331 |url=https://www.nytimes.com/1995/04/24/business/information-technology-the-executive-computer.html?scp=5&sq=vaporware&st=cse |access-date=2010-04-14}}</ref> Although Gates in November 1985 wrote "In the next 18 months, there is a good chance that Xenix system installations will be able to surpass the 400,000 system mark and achieve critical mass", he said that MS-DOS and Xenix "are separate products that address different markets" and "Microsoft does not intend to merge them into one OS"; in particular, "Multi-user capability will ''never'' be a feature of MS-DOS".<ref name="gates198511">{{Cite magazine |last=Gates |first=Bill |date=November 1985 |title=The Future of Xenix |url=https://archive.org/details/Unix_World_Vol02_10.pdf/page/n21/mode/1up?view=theater |access-date=2025-05-17 |magazine=[[UnixWorld]] |pages=20-37}}</ref> His company agreed with [[IBM]] to develop [[OS/2]],<ref name="letwin19950817">{{cite newsgroup |newsgroup=comp.os.ms-windows.misc|url=https://groups.google.com/forum/?hl=en#!original/comp.os.ms-windows.misc/-iNeep60eVE/Xl5ddAtJENcJ |title=What's happening to OS/2 |date=August 17, 1995 |access-date=November 6, 2013 |author-last=Letwin |author-first=Gordon |message-id=DDFvKo.G4M@lab.lwpi.com}}</ref> and its Xenix team (together with the best MS-DOS developers){{citation needed|date=August 2019}} was assigned to that project. In 1987, Microsoft transferred ownership of Xenix to SCO in an agreement that left Microsoft owning slightly less than 20% of SCO (this amount prevented both companies from having to disclose the exact amount in the event of an SCO IPO). SCO would acquire both of the other companies that had Xenix rights,<ref name="doug-video"/> [[Logica]]'s software products group in 1986 and HCR in 1990.<ref>{{cite news | url=https://books.google.com/books?id=gjwEAAAAMBAJ&pg=PA33 | title=Santa Cruz Operation Ltd. to Offer Source for Xenix | magazine=InfoWorld | date=December 8, 1986 | page=33}}</ref><ref>{{cite news | url=https://www.newspapers.com/image/463861965/?terms=hcr%2B%22santa%2Bcruz%2Boperation%22 | title=California firm acquires Unix-systems leader | agency=Canadian Press | newspaper=The Ottawa Citizen | date=May 10, 1990 | page=H8 | via=Newspapers.com}}</ref> When Microsoft eventually lost interest{{clarify|date=August 2019}} in OS/2 as well, the company based its further high-end strategy on [[Windows NT]].

In 1987, [[The Santa Cruz Operation|SCO]] ported Xenix to the [[Intel 80386|386]] processor, a [[32-bit]] chip, after securing knowledge from Microsoft insiders that Microsoft was no longer developing Xenix.<ref name="NYT"/> Xenix System V Release 2.3.1 introduced support for i386, [[SCSI]] and [[TCP/IP]]. SCO's Xenix System V/386 was the first 32-bit operating system available on the market for the x86 CPU architecture.

Microsoft continued to use Xenix internally. {{asof|1987}} Xenix handled 60,000 megabytes of email weekly on its [[MS-Net]] network.<ref name="flynn19870223">{{Cite magazine |last=Flynn |first=Laurie |date=1987-02-23 |title=Companywide Network A Necessity at Microsoft |url=https://books.google.com/books?id=1DAEAAAAMBAJ&pg=PA17#v=onepage&q&f=true |access-date=2025-05-21 |magazine=InfoWorld |page=17 |volume=9 |issue=8}}</ref> The company submitted a patch to support functionality in Unix to AT&T that year, which trickled down to the code base of both Xenix and SCO Unix. Microsoft is said to have used Xenix on [[Sun Microsystems|Sun]] workstations and [[VAX]] [[minicomputer]]s extensively within their company as late as 1988.<ref>{{cite newsgroup |title=Re: Microsoft Source (fwd) |author-first=Terry |author-last=Lambert |date=November 7, 2000 |newsgroup=sol.lists.freebsd.chat |message-id=200011062350.QAA25774_usr08.primenet.com@ns.sol.net |url=http://groups.google.com/group/sol.lists.freebsd.chat/msg/96c45193263f1698 |access-date=October 25, 2006}}</ref> All internal Microsoft email transport was done on Xenix-based [[Motorola 68000|68000]] systems until 1995–1996, when the company moved to its own [[Exchange Server]] product.<ref>{{cite web |title=Microsoft's Migration to Microsoft Exchange Server - The Evolution of Messaging within Microsoft Corporation |website=[[Microsoft]] |url=http://www.microsoft.com/technet/archive/itsolutions/intranet/build/exchgdep.mspx#EGAA |archive-url=https://web.archive.org/web/20050427212001/http://www.microsoft.com/technet/archive/itsolutions/intranet/build/exchgdep.mspx#EGAA |archive-date=April 27, 2005}}</ref> Microsoft chairman [[Bill Gates]] said at [[Unix Expo]] in 1996 that, for a long time, Microsoft had the highest-volume AT&T Unix license.<ref>{{cite web |date=October 9, 1996 |title=UNIX Expo — Remarks by Bill Gates |url=http://www.microsoft.com/billgates/speeches/industry&tech/uexpo.asp |archive-url=https://web.archive.org/web/20010818203946/http://www.microsoft.com/billgates/speeches/industry&tech/uexpo.asp |archive-date=August 18, 2001 |access-date=September 9, 2013 |website=[[Microsoft]]}}</ref>

=== Replacement ===
By 1988 AT&T reported that Xenix developers were about half of the 500,000 Unix licenses worldwide.<ref name="patton19880118">{{Cite magazine |last=Patton |first=Carole |date=18 January 1988 |title=AT&T Unix Standard Could Impact Santa Cruz Operation 
 |url=https://books.google.com/books?id=Dz8EAAAAMBAJ&pg=PA33#v=onepage&q&f=false |access-date=2025-05-25 |magazine=[[InfoWorld]] |page=33 |volume=10 |issue=3}}</ref> SCO released its [[SCO Unix]] as a higher-end product, based on System V R3 and offering a number of technical advances over Xenix; Xenix remained in the product line. In the meantime, AT&T and [[Sun Microsystems]] completed the merge of Xenix, BSD, [[SunOS]] and System V R3 into System V R4. The last version of SCO Xenix/386 itself was System V R2.3.4, released in 1991.<ref>{{harvnb|Pate|1996|page=10}}</ref>