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{{Short description|Operating system}}
{{Refimprove|article|date=April 2007}}
{{Infobox OS
| name                   = Convergent Technologies Operating System (CTOS)<!-- Name of program or distribution -->
| logo                   = <!-- filename only (no wikilink, no Image:/File:) -->
| logo caption           = 
| logo size              = 
| logo alt               = 
| screenshot             = CTOS-B25.JPG<!-- filename only (no wikilink, no Image:/File:) -->
| caption                = A Burroughs B25 computer running CTOS
| screenshot_size        = 
| screenshot_alt         = 
| collapsible            = 
| version of             = <!-- For articles about releases of operating systems ONLY -->
| developer              = [[Convergent Technologies]]<!-- Name of main developer or sponsor-->
| family                 = <!-- "Unix-like" or "Microsoft Windows" -->
| working state          = Discontinued<!-- "Current", "Discontinued" (operating systems), or "No longer supported" (releases) -->
| source model           = <!-- "Open source", "Closed source", or "Shared source" -->
| released               = {{Start date and age|1980}}
| discontinued           = <!-- DON'T use this for articles about releases of operating systems -->
| RTM date               = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} ONLY for articles about OS releases -->
| GA date                = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} ONLY for articles about OS releases -->
| latest release version = 
| latest release date    = 
| latest preview version = 
| latest preview date    = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} -->
| marketing target       = 
| programmed in          = [[PL/M]]
| language               = <!-- Supported human languages (English, French, Italian, Arabic, ...) -->
| update model           = <!-- APT, Windows Update, etc. -->
| package manager        = <!-- dpkg, rpm, Windows installer, etc. -->
| supported platforms    = [[x86]]<!-- IA-32, x64, Itanium, ARM, etc. -->
| kernel type            = [[Microkernel]]<!-- Hybrid, Monolithic, Microkernel, Exokernel, Nanokernel, etc. -->
| userland               = 
| ui                     = 
| license                = [[Proprietary software|Proprietary]]
| preceded by            = 
| succeeded by           = 
| website                = <!-- {{URL|www.example.org}} -->
| support status         = <!-- For articles about releases of operating systems ONLY -->
| other articles         = 
| prog_language          = 
}}

The '''Convergent Technologies Operating System''', also known variously as '''CTOS''', '''BTOS''' and '''STARSYS''', is a discontinued modular, [[message-passing]], multiprocess-based [[operating system]].

==Overview==
CTOS had many innovative features for its time. System access was controlled with a user password and volume or disk passwords. Each volume and directory were referenced with delimiters to identify them, and could be followed with a file name, depending on the operation, i.e. {Network Node}[VolumeName]<DirectoryName>FileName.

It was possible to custom-link the operating system to add or delete features.

CTOS supported a transparent [[peer-to-peer network]] carried over serial [[EIA-422|RS-422]] cables (daisy-chain topology) and in later versions carried over [[twisted pair]] ([[star topology]]) with [[RS-422]] adapters using CTOS Cluster Hub-R12 designed by Paul Jackson Ph.D. of SumNet Pty Limited in Australia. Each workgroup (called a "cluster") was connected to a server (called a "master").  The workstations, normally [[diskless workstation|diskless]], were [[Network booting|booted over the cluster network]] from the master, and could optionally be locally booted from attached hard drives.

The [[Inter-process communication]] (IPC) is primarily based on the "request" and "respond" messaging foundation that enhanced the Enterprise Application Integration among services for both internal and external environments. Thus CTOS was well known for the message-based [[Microkernel]] Architecture. Applications are added as services to the main server. Each client consumes the services via its own mailbox called "exchange" and well-published message formats. The communication works on "request codes" that are owned by the service. The operating system maintains the exchanges, message queues, scheduling, control, message passing, etc., while the service manages the messages at its own exchange using "wait", "check", and "respond" macros.

CTOS ran on [[Intel]] [[x86]] computers, and could run concurrently with [[Windows NT]] on [[Unisys]] PC.

The system [[API]] was presented to both [[high-level language]]s and [[assembly language]].

==Programs==
The assembler was very advanced, with a [[Lisp (programming language)|Lisp]]-like pattern-matching macro facility unmatched by almost any other assembler before or since. There was an always-resident debugger.

Most of the system programs were written in [[PL/M]], an [[ALGOL]]-like language from [[Intel]] which compiled directly to [[object code]] without a [[runtime library]].

The [[word processor]] was one of the first screen-oriented editors with many high-powered features, such as multiple views of the same file, cut/copy/paste, unlimited undo/redo, no typing lost after a crash or power failure, user-selectable fonts, and much more.

The spreadsheet allowed blocks of cells to be protected from editing or other user input. The BTOS version allowed scripts to be written that included opening the spreadsheet for user input, then automatically printing graphs based on the input data.

The system shell was extensible, making it possible to define new commands. To get the parameters, the system would display the form which was to be filled out by the user. The input form had conventions for mandatory and optional input fields, which made it very easy to train new users.

==Usage==
[[Convergent Technologies]]' first product was the IWS (Integrated Workstation) based on the [[Intel 8086]] processor, which had CTOS as its operating system. This was a modular operating system with built-in [[local area networking]]. CTOS supported multiple processes or threads, and message-based interprocess communication.<ref name="foldoc">{{foldoc|Convergent+Technologies+Operating+System}}</ref>

Companies that licensed CTOS included [[Groupe Bull|Bull]] (STARSYS), and [[Burroughs Corporation|Burroughs]] (BTOS) who later merged with Sperry to become [[Unisys]]. Unisys was the single largest customer and acquired Convergent Technologies in 1988. At its peak, CTOS had over 800,000 users worldwide.

CTOS is no longer marketed to new customers. Former major customers included police forces, banks, airlines, [[Nationwide Insurance]],<ref>{{cite magazine |title=When the mission is critical, leaders plug into BTOS workstations |url=https://books.google.com/books?id=qQUAAAAAMBAJ&pg=PA32 |magazine=CIO |date=November 1989}}</ref> [[U-Haul]],<ref>{{cite news |title=Burroughs contracts with U-Haul |url=https://books.google.com/books?id=mop2UUCt4kIC&pg=PA15 |work=ComputerWorld |date=June 23, 1986 |page=15}}</ref> the [[U.S. Postal Service]], the [[Drug Enforcement Administration]], the [[U.S. Army]] and the [[United States Coast Guard]]. The Coast Guard used the operating system from approximately 1984 until 2000.  In Australia, CTOS/BTOS was used by the [[Trade Practices Commission]], [[Auditor-General of New South Wales|NSW Auditor-General]]'s, CSIRO, Commonwealth Electoral Office, Western Australia Prisons Department and many commercial banks.

Some Convergent systems used the [[Intel 80186]] processor, a processor seldom used by standard PCs.

[[Progress Software Corporation]] made a commercial database application for CTOS that was in [[4GL]]. The [[United States Coast Guard]] used these databases for logistics administration for their vessels.

There was a port of [[CorelDRAW]] for CTOS running the [[Presentation Manager]].

==References==
{{Reflist}}
* {{cite book
  | first1 = Edna Ilyin
  | last1 = Miller
  | first2 = Jim
  | last2 = Crook
  | first3 = June
  | last3 = Loy 
  | title = Exploring CTOS
  | publisher = [[Prentice Hall]]
  | year = 1991
  | isbn = 0-13-297342-1 
  | url  = https://archive.org/details/bitsavers_convergentS1991_11080831 }}

==External links==
*[https://web.archive.org/web/20110708212436/http://www.ctosfaq.com/CtosFaqOct1999.htm The CTOS FAQ October 1999]
*[https://web.archive.org/web/20080828190425/http://www.byte.com/art/9412/sec13/art2.htm CTOS Revealed, Byte, December 1994]
*[https://www.angelfire.com/ga/paulmooney/ctos.html Paul Mooney's CTOS Central]
*[https://web.archive.org/web/20111020190645/http://www.ctosfaq.com/CTOSPictures.htm The CTOS FAQ Picture Archive]
*[http://www.softwarepreservation.org/meetings/2006/2006-05-17/CTOS_Intro_2006_05_17.pdf Exhuming CTOS: The Convergent Technologies Project, Nadia Ilyin]
*[http://bitsavers.org/pdf/convergent Convergent archive] at bitsavers.org

{{Operating system}}

[[Category:1980 software]]
[[Category:Discontinued operating systems]]
[[Category:Proprietary operating systems]]
[[Category:Unisys operating systems]]
[[Category:X86 operating systems]]