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THEOS, which translates from Greek as "God", is an operating system which started out as OASIS, a microcomputer operating system for small computers that use the Z80 processor. Originally written in the late 1970s by Timothy S. Williams as a low-cost alternative to the more expensive mini- and mainframe- computers that were popular in the day, OASIS provided time-sharing multiuser facilities to allow several users to utilise the resources of one computer. Similar in concept to MP/M or UNIX, THEOS uses external device drivers rather than a kernel, allowing it to be more portable to other environments, though support has been primarily directed towards industry-standard hardware (i.e. PC's). THEOS is specifically aimed at small business users, with a wide range of vertical-market applications packages being developed and supported by individuals and companies.

THEOS operating systems have been distributed by THEOS Software Corporation in Walnut Creek, California, since 1983. As of 2003, Phase One Systems publishes software development tools for THEOS(R) systems. As well as porting tools, Phase One Systems distributed the Freedom query package and Control database package for THEOS systems, used to bring SQL-like data extraction tools to third-party software packages.

The languages distributed with THEOS include THEOS Multi-User Basic and C. A powerful EXEC shell language can be used for task automation or to produce a turnkey system.

When the operating system was launched for the IBM Personal Computer/AT in 1982, the decision was taken to change the name from OASIS to THEOS, short for THE Operating System.

A number of security features exist, including dynamic passwords (where the password includes part of the date or time, or client IP address, or other dynamic elements), allow/deny security, a comprehensive inbound and outbound firewall, and an option to require a certain level of encryption in the workstation connection. In addition, the object file format is proprietary, and the operating system uses Intel "protected mode" to further increase defence against buffer overrun attacks.

THEOS was introduced in Europe by Fujitsu and other hardware manufacturers 30 years ago, and is distributed by a number of distributors in Great Britain, Spain, Portugal, Germany, Italy and more. The 'current' version is THEOS Corona Commercial Release 6, which was released in December 2008, and a number of updates have been released since that time. The current Windows Workstation Client (as of May 2009) is version 3.16 from July 2003.


OASIS operating system
DeveloperPhase One Systems
Initial release1977
Available inEnglish

The OASIS operating system was originally developed and distributed in 1977 by Phase One Systems of Oakland, California (President Howard Sidorsky). OASIS was developed for the Z80 processor and was the first multi-user operating system for 8-bit microprocessor based computers (Z-80 from Zilog). "OASIS" was a backronym for "Online Application System Interactive Software".

OASIS consisted of a multi-user operating system, a powerful Business Basic/Interpreter, C compiler and a powerful text editor. Timothy Williams developed OASIS and was employed at Phase One. The market asked for 16-bit systems but there was no real 16-bit multi-user OS for 16-bit systems. Every month Phase One announced OASIS-16 but it did not come. One day Timothy Williams claimed that he owned OASIS and started a courtcase against Phase One and claimed several million U.S. dollars. Sidorsky had no choice and claimed Chapter 11. The court case took two years and finally the ruling was that Timothy Williams was allowed to develop the 16-bit version of OASIS but he was not allowed to use the OASIS name anymore.

As an alternate history, presented by David Shirley at the Computer Information Centre, an OASIS distributor for the UK in the early 1980s, is that Timothy Williams developed the OASIS operating system and contracted with Phase One Systems to market and sell the product. Development of the 16-bit product was under way but the product was pre-announced by POS, leading to pressure to release it early when it was not properly debugged or optimised. (OASIS 8-bit was quite well optimised by that point, with many parts hand-coded in Z80 assembler, which meant that most early then-new 16-bit systems performed nowhere near as well as their 8-bit counterparts). This situation led to Williams becoming dissatisfied with the Phase One company at the time, and forming his own company to market and support the product. The company was initially called Oasis Technologies, until Phase One took action to protect the name which they considered to be theirs, so rather than fight a long and expensive court battle, the company and product was renamed "THEOS".

Williams created a new company and product name: "THEOS" meaning "the OS" in the sense of "the one" ("Theos" is Greek for "God"). While Williams and Sidorsky where fighting in the court the manufacturers had no 16-bit multi-user OS. That led to the agreement between Microsoft and Altos to make a commercial usable version of the only academically available os UNIX 7 from Bell Labs, which they called Xenix.[dubious ] It was a joint development and the Altos version would be AMEX (Altos multiuser executive). Microsoft would distribute the product via Santa Cruz Operation. Seiko also lost patience with Williams and decided to make their own OASIS 16-bit version and hired Dr. Jeffrey Bahr. When Xenix and THEOS became available Seiko did decide to leave this market. Jeffrey Bahr started CET which went on with the development of the 16-bit OASIS compatible software. CET software was complete compatible with OASIS/THEOS and allowed these users to go into the Unix and Microsoft world.

Cet acquired the Phase one company. Also, Phase One Systems licenses a porting tool called CET Basic. CET Basic is compatible with THEOS BASIC, MultiUser BASIC, OASIS BASIC, and UX-BASIC. This means you can keep most of your existing source code, and using W/32 BASIC, recompile your THEOS, OASIS, or UX-BASIC programs to work under additional operating systems such as Microsoft Windows, Linux or SCO UNIX.


BYTE in 1985 stated that "the functionality of THEOS is somewhere between MS-DOS and UNIX". The magazine criticized the documentation's quality, and concluded that the price was too high compared to other multiuser operating systems for the PC such as Pick and Coherent.[1]

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  1. ^ Rochkind, Marc J. (Fall 1985). "Pick, Coherent, and THEOS". BYTE. p. 231. Retrieved 19 March 2016.

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