Xenix under Bochs
|Company / developer||Microsoft|
|Source model||Closed source|
|Latest stable release||2.3.4 / 1989|
|Supported platforms||PC/XT, x86, PDP-11, Z8001, 68k|
|Kernel type||Monolithic kernel|
Xenix is a discontinued version of the Unix operating system, licensed by Microsoft from AT&T Corporation in the late 1970s. The Santa Cruz Operation (SCO) later acquired exclusive rights to the software, and eventually superseded it with SCO UNIX (now known as SCO OpenServer).
In the late 1980s, Xenix was "probably the most widespread version of the UNIX operating system, according to the number of machines on which it runs", according to developers of the BSD version of Unix, and Microsoft chairman Bill Gates stated in 1996 that for a long time, his firm had the highest-volume AT&T Unix license.
Bell Labs, Unix's developer, was part of the regulated Bell System and could not sell Unix. It instead licensed the software to others. 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 1979, and announced on August 25, 1980 that it would make it available for the 16-bit microcomputer market. The initial port of Xenix was to the Zilog Z8000 series and subsequently to the Intel 8086/8088 architecture ported by The Santa Cruz Operation.
Microsoft did not sell Xenix directly to end users; instead, they licensed it to software OEMs such as IBM, Intel, Tandy, Altos, SCO, and Siemens (SINIX) who then ported it to their own proprietary computer architectures. Microsoft Xenix originally ran on the PDP-11; the first port was for the Zilog Z8001 16-bit processor. Altos shipped a version for their Intel 8086 based computers early in 1982, Tandy Corporation shipped TRS-XENIX for their 68000-based systems in January 1983, and SCO released their port to the IBM PC in September 1983. A port to the 68000-based Apple Lisa also existed. At the time, Xenix was based on AT&T's UNIX System III.
Version 2.0 of Xenix was released in 1985 and was based on UNIX System V. An update numbered 2.1.1 added support for the Intel 80286 processor. The Sperry PC/IT, an IBM PC AT clone, was advertised as capable of supporting eight simultaneous dumb terminal users under this version. Subsequent releases improved System V compatibility.
In 1987, SCO ported Xenix to the 386 processor, a 32-bit chip. Xenix 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.
After the breakup of the Bell System AT&T started selling Unix. Microsoft, believing that it could not compete with Unix's developer, decided to abandon Xenix. An agreement was signed with IBM to develop OS/2, and the Xenix team (together with the best MS DOS developers) was assigned to that project. In 1987 Microsoft transferred ownership of Xenix to SCO in an agreement that left Microsoft owning 25% of SCO. When Microsoft eventually lost interest in OS/2 as well, it based its further high-end strategy on Windows NT.
Microsoft continued to use Xenix internally, submitting a patch to support functionality in UNIX to AT&T in 1987, which trickled down to the code base of both Xenix and SCO UNIX. Microsoft is said to have used Xenix on Sun workstations and VAX minicomputers extensively within their company as late as 1992. All internal Microsoft email transport was done on Xenix-based 68000 systems until 1995-96, when the company moved to its own Exchange Server product.
SCO first released SCO UNIX as a higher-end product, based on System V Release 3 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 into System V Release 4. SCO UNIX was still based on SVR3, but had most features of Release 4. The last version of Xenix itself was 2.3.4.
Aside from its AT&T Unix base (Version 7, System III and System V), Xenix incorporated elements from BSD, notably the vi text editor and its supporting libraries (termcap and curses). Its kernel featured some original extensions by Microsoft, notably file locking and semaphores,:1.12 while to the userland Microsoft added a "visual shell" for menu-driven operation instead of the traditional Unix shell. A limited form of local networking over serial lines (RS-232 ports) was possible through the "micnet" software, which supported file transfer and electronic mail, although UUCP was still used for networking via modems.
Trusted Xenix was a variant developed by Trusted Information Systems which incorporated the Bell-La Padula model of multilevel security, and had a multilevel secure interface for the STU-III secure communications device (that is, an STU-III connection would only be made available to applications running at the same privilege level as the key loaded in the STU-III). It was evaluated by formal methods and achieved a B2 security rating under the DoD's Trusted Computer System Evaluation Criteria—the second highest rating ever achieved by an evaluated operating system. Version 2.0 was released in January 1991, version 3.0 in April 1992, and version 4.0 in September 1993. It was still in use as late as 1995.
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- Photograph, requirements, and description of SCO Xenix 386 circa-1988
- Softpanorama take on Xenix development
- German Site about the history of Xenix
- Tandy Images for Download
- Xenix documentation and books for Download
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- Intel Multibus System 320 for Xenix (or iRMX86)
- Welcome to comp.unix.xenix.sco (v 1.64)