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THEOS, which translates from Greek as "God", is anoperating system which started out asOASIS, amicrocomputeroperating system for small computers that use theZ80 processor. When the operating system was launched for theIBM Personal Computer/AT in 1982, the decision was taken to change the name from OASIS to THEOS, short forTHE Operating System.

TheOASIS operating system was originally developed and distributed in 1977 by Phase One Systems ofOakland, California (President Howard Sidorsky). OASIS was developed for theZ80 processor and was the first multi-user operating system for 8-bit microprocessor based computers (Z-80 fromZilog). "OASIS" was abackronym for "OnlineApplicationSystemInteractiveSoftware".

OASIS consisted of a multi-user operating system, a powerfulBusiness Basic/Interpreter,Ccompiler and a powerfultext 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^[1] but it did not come. One day Timothy Williams claimed that he owned OASIS and started a court case against Phase One and claimed several millionU.S. dollars. Sidorsky had no choice and claimedChapter 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.

David Shirley presented an alternative history at the Computer Information Centre, an OASIS distributor for the UK in the early 1980s. He said Timothy Williams developed the OASIS operating system and contracted with Phase One Systems to market and sell the product. Development was underway, but it was prematurely announced by POS. This led to pressure to release OASIS early, when it was still not properly debugged or optimised. OASIS 8-bit was quite well optimised by that point, with many partshand-coded in Z80assembler, but that meant then-new 16-bit systems performed nowhere near as well as their 8-bit counterparts. This situation led to Williams becoming dissatisfied with Phase One, and forming his own company to market and support the 16-bit OASIS. This new company was initially called Oasis Technologies, until Phase One took action to protect the name. Rather than fight a long and expensive court battle, Williams renamed the company and product to "THEOS". It was intended to mean "the OS" in the sense of "the one" ("Theos" isGreek for "God").

While Williams and Sidorsky fought in court, manufacturers had no 16-bit multi-user OS. This led to an agreement betweenMicrosoft andSanta Cruz Operation to make a new operating system based onVersion 7 Unix fromBell Labs. Microsoft purchased a license for Version 7 UNIX fromAT&T in 1978,^[2] and announced on August 25, 1980, that it would make it available for the16-bit microcomputer market.^[3] Because Microsoft was not able to license the "UNIX" name itself,^[4] it was calledXenix. Microsoft would distribute the product via Larry Michels and his son Doug Michels (Santa Cruz Operation).

Seiko also lost patience with THEOS and 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 completely compatible with OASIS/THEOS and allowed users entry to 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 existingsource code, and using W/32 BASIC, recompile your THEOS, OASIS, or UX-BASIC programs to work under additional operating systems such asMicrosoft Windows,Linux orSCO UNIX.

THEOS operating systems have been distributed byTHEOS Software Corporation inWalnut 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 bringSQL-like data extraction tools to third-party software packages.

THEOS was introduced in Europe byFujitsu 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.

Originally written in the late 1970s by Timothy S. Williams as a low-cost alternative to the more expensivemini- andmainframe- computers that were popular in the day, OASIS provided time-sharingmultiuser facilities to allow several users to utilise the resources of one computer. Similar in concept toMP/M orUNIX, THEOS uses externaldevice drivers rather than akernel, 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 ofvertical-market applications packages being developed and supported by individuals and companies.

The languages distributed with THEOS include THEOS Multi-UserBasic andC. A powerful EXECshell language can be used for task automation or to produce aturnkey system.

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

The following list ofcommands are supported by the THEOS/OASIS Command String Interpreter (CSI).^[5]

BYTE in 1985 stated that "the functionality of THEOS is somewhere betweenMS-DOS andUNIX". 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 asPick andCoherent.^[6]

• Multiuser DOS Federation

• THEOS Software Corporation
• Historia de OASIS®/THEOS® Corona
• OASIS Users' Group Archive February 1981 through November 1985

• Proprietary operating systems
• X86 operating systems
• 1977 software

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