Editing Compatible Time-Sharing System (section)

{{Short description|Computer operating system}}
{{distinguish|CICS}}
{{Infobox OS
| name                   = Compatible Time-Sharing System (CTSS)
| logo                   = 
| screenshot             = CTSS_Scheduler_in_MAD_and_FAP.png
| caption                = Preamble of two versions of the CTSS scheduler, one in [[MAD (programming language)|MAD]] and one in [[FAP assembly|FAP]]
| developer              = [[MIT Computation Center]], [[MIT Computer Science and Artificial Intelligence Laboratory#Project MAC|Project MAC]]
| source_model           = [[Open source]]
| kernel_type            = [[Monolithic kernel|Monolithic]], protected
| supported_platforms    = [[IBM 7090]], [[IBM 7094]]
| ui                     = [[Command-line interface]]
| family                 = 
| released               = {{Start date and age|1961}}
| latest_release_version = 
| latest_release_date    = 
| latest_test_version    = 
| latest_test_date       = 
| marketing_target       = Colleges and universities<ref name="50th" />
| programmed_in          = [[FAP assembly]], [[MAD (programming language)|MAD]]
| prog_language          = FAP assembly, MAD, [[Fortran]], [[LISP]]
| language               = [[English language|English]]
| updatemodel            = 
| package_manager        = 
| working_state          = Discontinued, simulator available
| license                = {{data missing|date=May 2021}}
| preceded by            = 
| succeeded by           = [[Multics]]
| website                = {{URL|www.cozx.com/dpitts/ibm7090.html}}
}}
{{History of IBM mainframe operating systems|early}}
The '''Compatible Time-Sharing System''' ('''CTSS''') was the first general purpose [[time-sharing]] [[operating system]].<ref>{{cite web |url=http://broadcast.oreilly.com/2009/04/an-interview-with-brian-kernig.html |title=An Interview with Brian Kernighan: Breeding Little Languages |last=Noren |first=Allen |date=April 10, 2009 |website=O'Reilly Community |access-date=July 28, 2023 |archive-url=https://web.archive.org/web/20170630062507/http://broadcast.oreilly.com/2009/04/an-interview-with-brian-kernig.html |archive-date=June 30, 2017 |quote=I was using CTSS, the first time-sharing system}}</ref><ref>{{cite report |last1=Singh |first1=Jai P. |last2=Morgan |first2=Robert P. |date=October 1971 |title=Educational Computer Utilization and Computer Communications |url=https://files.eric.ed.gov/fulltext/ED057575.pdf |publisher=Washington University |location=St. Louis, MO |id=National Aeronautics and Space Administration Grant No. Y/NGL-26-008-054 |page=13 |access-date=March 8, 2022 |quote=Much of the early development in the time-sharing field took place on university campuses.<sup>8</sup> Notable examples are the CTSS (Compatible Time-Sharing System) at MIT, which was the first general purpose time-sharing system... |archive-date=March 19, 2023 |archive-url=https://web.archive.org/web/20230319003544/https://files.eric.ed.gov/fulltext/ED057575.pdf |url-status=live }}</ref> Compatible Time Sharing referred to time sharing which was compatible with [[batch processing]]; it could offer both time sharing and batch processing concurrently.

CTSS was developed at the [[MIT Computation Center]] ("Comp Center"). CTSS was first demonstrated on MIT's modified [[IBM 709]] in November 1961. The hardware was replaced with a modified [[IBM 7090]] in 1962 and later a modified [[IBM 7094]] called the "blue machine" to distinguish it from the Project MAC CTSS IBM 7094. Routine service to MIT Comp Center users began in the summer of 1963 and was operated there until 1968.

A second deployment of CTSS on a separate IBM 7094 that was received in October 1963 (the "red machine") was used early on in [[MIT Computer Science and Artificial Intelligence Laboratory#Project MAC|Project MAC]] until 1969 when the red machine was moved to the Information Processing Center<ref>{{cite news |url=https://www.nytimes.com/1968/11/11/archives/new-information-center-will-open-at-mit-today.html |title=New Information Center Will Open at MIT Today |newspaper=[[The New York Times]] |date=November 11, 1968}}</ref> and operated until July 20, 1973. CTSS ran on only those two machines; however, there were remote CTSS users outside of MIT including ones in California, South America, the [[University of Edinburgh]] and the [[University of Oxford]].<ref name="50th">{{cite web |url=https://multicians.org/thvv/compatible-time-sharing-system.pdf |title=Compatible Time-Sharing System (1961-1973): Fiftieth Anniversary Commemorative Overview |editor-last1=Walden |editor-first1=David |editor-last2=Van Vleck |editor-first2=Tom |editor2-link=Tom Van Vleck |date=2011 |publisher=IEEE Computer Society |access-date=February 20, 2022 |archive-date=October 9, 2022 |archive-url=https://ghostarchive.org/archive/20221009/https://multicians.org/thvv/compatible-time-sharing-system.pdf |url-status=live }}</ref><ref name="ctsspg69">{{cite book |url=http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide_Dec69.pdf |title=The Compatible Time-Sharing System, A Programmer's Guide |edition=Second |editor-last=Crisman |editor-first=Patricia A. |date=December 31, 1969 |publisher=The M.I.T Computation Center |access-date=March 10, 2022 |archive-date=June 25, 2024 |archive-url=https://web.archive.org/web/20240625150328/http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide_Dec69.pdf |url-status=live }}</ref>