Editing Time-sharing

{{Short description|Computing resource shared by concurrent users}}
{{About|the computing term|the type of property ownership|Timeshare|time sharing of communications media|Time-division multiple access|the 1986 novel by Richard Krawiec|Time Sharing (novel)}}

{{History of computing}}
In [[computing]], '''time-sharing''' is the [[Concurrency (computer science)|concurrent]] sharing of a computing resource among many tasks or users by giving each [[Process (computing)|task]] or [[User (computing)|user]] a small slice of [[CPU time|processing time]]. This quick switch between tasks or users gives the illusion of [[Parallel computing|simultaneous]] execution.<ref>{{Cite web |date=2023-11-23 |title=Time-sharing definition – Glossary {{!}} NordVPN |url=https://nordvpn.com/pt/cybersecurity/glossary/time-sharing/ |access-date=2024-06-17 |website=nordvpn.com |language=pt}}</ref><ref>{{Cite web |date=2020-04-28 |title=Time Sharing Operating System |url=https://www.geeksforgeeks.org/time-sharing-operating-system/ |access-date=2024-06-17 |website=GeeksforGeeks |language=en-US}}</ref> It enables [[computer multitasking|multi-tasking]] by a single user or enables multiple-user sessions.

Developed during the 1960s, its emergence as the prominent model of computing in the 1970s represented a major technological shift in the history of computing. By allowing many users to interact [[concurrent computing|concurrently]] with a single computer, time-sharing dramatically lowered the cost of providing computing capability, made it possible for individuals and organizations to use a computer without owning one,<ref>IBM advertised, early 1960s, with a headline: "This man is sharing a $2 million computer"</ref> and promoted the [[Interactive computing|interactive use of computers]] and the development of new interactive [[application software|application]]s.

==History==

===Batch processing===
{{Main|Batch processing}}
The earliest computers were extremely expensive devices, and very slow. Machines were typically dedicated to a particular set of tasks and operated by control panels, the operator manually entering small programs via switches one at a time. These programs might take hours to run. As computers increased in speed, [[Runtime (program lifecycle phase)|run times]] dropped, and soon the time taken to start up the next program became a concern. Newer [[batch processing]] software and methodologies, including batch operating systems such as [[IBM 7090/94 IBSYS|IBSYS]] (1960), decreased these "dead periods" by queuing up programs ready to run.<ref>{{cite web |url=https://courses.cs.washington.edu/courses/cse451/16wi/readings/lecture_readings/LCM_OperatingSystemsTimeline_Color_acd_newsize.pdf |title=History of Operating Systems}}</ref>

Comparatively inexpensive [[card punch]] or [[paper tape]] writers were used by programmers to write their programs "offline". Programs were submitted to the operations team, which scheduled them to be run. Output (generally printed) was returned to the programmer. The complete process might take days, during which time the programmer might never see the computer. Stanford students made a short film humorously critiquing this situation.<ref>{{Cite web |title=Ellis D. Kropotchev Silent Film - CHM Revolution |url=https://www.computerhistory.org/revolution/punched-cards/2/211/2253 |access-date=2023-05-26 |website=www.computerhistory.org}}</ref>

The alternative of allowing the user to operate the computer directly was generally far too expensive to consider. This was because users might have long periods of entering code while the computer remained idle. This situation limited interactive development to those organizations that could afford to waste computing cycles: large universities for the most part.

===Time-sharing===
[[File:Unix Timesharing UW-Madison 1978.jpeg|thumb|[[Unix]] time-sharing at the [[University of Wisconsin]], 1978]]

The concept is claimed to have been first described by Robert Dodds in a letter he wrote in 1949 although he did not use the term ''time-sharing''.<ref name="Lee1992">{{cite journal |last1=Lee |first1=J.A.N. |title=Claims to the term 'time-sharing' |journal=IEEE Annals of the History of Computing |date=1992 |volume=14 |issue=1 |pages=16–54 |doi=10.1109/85.145316 |s2cid=30976386 }}</ref> Later [[John Backus]] also described the concept, but did not use the term, in the 1954 summer session at [[Massachusetts Institute of Technology|MIT]].<ref name="jbackus">Backus, John, ''[http://bitsavers.org/pdf/mit/whirlwind/summer_session_1954/Digital_Computers_Advanced_Coding_Techniques_Summer_1954.pdf Digital Computers: Advanced Coding Techniques] {{Webarchive|url=https://web.archive.org/web/20220806082146/http://bitsavers.org/pdf/mit/whirlwind/summer_session_1954/Digital_Computers_Advanced_Coding_Techniques_Summer_1954.pdf |date=2022-08-06 }}'', MIT 1954, page 16-2. The first known description of computer time-sharing.</ref> [[Bob Bemer]] used the term ''time-sharing'' in his 1957 article "How to consider a computer" in ''Automatic Control Magazine'' and it was reported the same year he used the term ''time-sharing'' in a presentation.<ref name="Lee1992"/><ref>{{cite web |last1=Bemer |first1=Bob
|title=Origins of Timesharing |url=http://www.bobbemer.com/TIMESHAR.HTM |website=bobbemer.com
|date=March 1957 |access-date=June 24, 2016 |url-status = dead
|archive-url = https://web.archive.org/web/20170702215126/http://www.bobbemer.com/TIMESHAR.HTM
|archive-date = 2017-07-02}}</ref><ref>{{cite arXiv |last1=Middleburg |first1=C.A.
|title=Searching Publications on Operating Systems |eprint=1003.5525 |class=cs.OS |year=2010}}</ref> In a paper published in December 1958, W. F. Bauer wrote that "The computers would handle a number of problems concurrently. Organizations would have input-output equipment installed on their own premises and would buy time on the computer much the same way that the average household buys power and water from utility companies."<ref name="wfbauer">{{cite conference |last1=Bauer |first1=W. F. |title=Computer design from the programmer's viewpoint] |url=https://www.computer.org/web/csdl/index/-/csdl/proceedings/afips/1958/5053/00/50530046.pdf |conference=[[Joint Computer Conference|Eastern Joint Computer Conference]] |archive-url=https://web.archive.org/web/20160723012920/https://www.computer.org/web/csdl/index/-/csdl/proceedings/afips/1958/5053/00/50530046.pdf |archive-date=2016-07-23 |date=December 1958 |quote=One of the first descriptions of computer time-sharing. |url-status=dead}}</ref>

[[Christopher Strachey]], who became [[University of Oxford|Oxford University's]] first professor of computation, filed a patent application in the United Kingdom for "time-sharing" in February 1959.<ref>{{Cite web|title=Computer Pioneers - Christopher Strachey|url=https://history.computer.org/pioneers/strachey.html|access-date=2020-01-23|website=history.computer.org|quote=What Strachey proposed in his concept of time-sharing was an arrangement that would preserve the direct contact between programmer and machine, while still achieving the economy of multiprogramming.}}</ref><ref>{{Cite web|title=Computer - Time-sharing and minicomputers|url=https://www.britannica.com/technology/computer/Time-sharing-and-minicomputers|access-date=2020-01-23|website=Encyclopedia Britannica|language=en|quote=In 1959 Christopher Strachey in the United Kingdom and John McCarthy in the United States independently described something they called time-sharing.}}</ref> He gave a paper "Time Sharing in Large Fast Computers"<ref>{{cite conference |conference=UNESCO Information Processing conference |last1=Strachey |first1=Christopher |author1-link=Christopher Strachey |title=Time sharing in large fast computers |url=https://archive.org/details/large-fast-computers/ |access-date=30 May 2023 |date=1959-06-15}}</ref> at the first [[International Federation for Information Processing#History|UNESCO Information Processing Conference]] in Paris in June that year, where he passed the concept on to [[J. C. R. Licklider]].<ref>{{Cite book|last1=Gillies|first1=James M.|url=https://archive.org/details/howwebwasbornsto00gill/page/12/mode/2up?q=strachey|title=How the Web was Born: The Story of the World Wide Web|last2=Gillies|first2=James|last3=Gillies|first3=James|last4=Cailliau|first4=Robert|date=2000|publisher=Oxford University Press|isbn=978-0-19-286207-5|pages=13|language=en|url-access=registration}}</ref> This paper was credited by the [[MIT Computation Center]] in 1963 as "the first paper on time-shared computers".<ref name="ctsspg">F. J. Corbató, et al., ''[http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide.pdf The Compatible Time-Sharing System A Programmer's Guide]'' (MIT Press, 1963) {{ISBN|978-0-262-03008-3}}. "To establish the context of the present work, it is informative to trace the development of time-sharing at MIT. Shortly after the first paper on time-shared computers by C. Strachey at the June 1959 UNESCO Information Processing conference, H.M. Teager and J. McCarthy delivered an unpublished paper "Time-Shared Program Testing" at the August 1959 ACM Meeting."</ref>

The meaning of the term ''time-sharing'' has shifted from its original usage. Up until 1960, time-sharing was used to refer to [[multiprogramming]] without multiple user sessions.<ref name="Lee1992"/> Later, it came to mean sharing a computer [[Interactive computing|interactively]] among multiple users. In 1984 Christopher Strachey wrote he considered the change in the meaning of the term ''time-sharing'' a source of confusion and not what he meant when he wrote his paper in 1959.<ref name="Lee1992"/>

There are also examples of systems which provide multiple user consoles but only for specific applications, they are not general-purpose systems. These include [[Semi-Automatic Ground Environment|SAGE]] (1958), [[Sabre (travel reservation system)|SABRE]] (1960)<ref name="Lee1992" /> and [[PLATO (computer system)|PLATO II]] (1961), created by [[Donald Bitzer]] at a public demonstration at [[Robert Allerton Park]] near the University of Illinois in early 1961. Bitzer has long said that the PLATO project would have gotten the patent on time-sharing if only the University of Illinois had not lost the patent for two years.<ref>Brian Dear, Chapter 4 -- The Diagram, [https://books.google.com/books?id=D5ZBDwAAQBAJ&pg=PA71 The Friendly Orange Glow], Pantheon Books, New York, 2017; pages 71-72 discuss the development of time-sharing and the University of Illinois loss of the patent.</ref>

The first [[Interactivity|interactive]], general-purpose time-sharing system usable for software development, [[Compatible Time-Sharing System]], was initiated by [[John McCarthy (computer scientist)|John McCarthy]] at MIT writing a memo in 1959.<ref>{{Cite web |title=Reminiscences on the Theory of Time-Sharing |url=http://jmc.stanford.edu/computing-science/timesharing.html |access-date=2020-01-23 |website=John McCarthy's Original Website |quote=in 1960 'time-sharing' as a phrase was much in the air. It was, however, generally used in my sense rather than in John McCarthy's sense of a CTSS-like object.}}</ref> [[Fernando J. Corbató]] led the development of the system, a prototype of which had been produced and tested by November 1961.<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}}</ref> [[Philip M. Morse]] arranged for IBM to provide a series of their mainframe computers starting with the [[IBM 704]] and then the [[IBM 709]] product line [[IBM 7090]] and [[IBM 7094]].<ref name="50th" /> IBM loaned those mainframes at no cost to MIT along with the staff to operate them and also provided hardware modifications mostly in the form of [[Request price quotation|RPQ]]s as prior customers had already commissioned the modifications.<ref>{{cite book |last=Watson Jr. |first=Thomas J. |author-link=Thomas J. Watson Jr. |date=1990 |title=Father, Son, and Co.: My Life at IBM and Beyond |location=New York |publisher=Bantam Books |page=244-245 |isbn=9780553070118 |quote=When we started delivering our first commercial machines, our customers often found that the most difficult thing about having a computer was finding somebody who could run it. We couldn't produce all those technicians ourselves. Yet there was not a single university with a computer curriculum. So I went up to MIT in the mid-1950s and urged them to start training computer scientists. We made a gift of a large computer and the money to run it.}}</ref><ref name="50th" /> There were certain stipulations that governed MIT's use of the loaned IBM hardware. MIT could not charge for use of CTSS.<ref>{{cite journal |last1=Lee |first1=J.A.N. |last2=Rosin |first2=Robert F |date=1992 |title=Time-Sharing at MIT |url=https://archive.org/details/time-sharing-at-mit |journal=IEEE Annals of the History of Computing |volume=14 |issue=1 |pages=18 |doi=10.1109/85.145317 |s2cid=30631012 |access-date=October 3, 2022 | quote=Corbato: No, that was one of the interesting aspects. One of the terms of IBM's donation for the use of the equipment was that we were not to charge for it. It was free all right.}}</ref> MIT could only use the IBM computers for eight hours a day; another eight hours were available for other colleges and universities; IBM could use their computers for the remaining eight hours, although there were some exceptions. In 1963 a second deployment of CTSS was installed on an IBM 7094 that MIT has purchased using [[DARPA|ARPA]] money. This was used to support [[Multics]] development at [[Project MAC]].<ref name="50th" />

[[JOSS]] began time-sharing service in January 1964.<ref>{{cite book | chapter=JOSS: a designer's view of an experimental on-line computing system | author = J. C. Shaw | title=Proceeding AFIPS '64 (Fall, part I) Proceedings of the October 27-29, 1964, fall joint computer conference, part I | year=1964 | pages=455–464 | doi = 10.1145/1464052.1464093 | isbn = 9781450378895 | s2cid = 16483923 | chapter-url=http://dl.acm.org/citation.cfm?id=1464093}}</ref> [[Dartmouth Time-Sharing System]] (DTSS) began service in March 1964.<ref name="Rankin">{{Citation | last = Rankin| first = Joy Lisi | title = A People's History of Computing in the United States | place = Cambridge, Massachusetts | publisher = Harvard University Press | year = 2018| isbn = 9780674970977 }}</ref>

===Development===
Throughout the late 1960s and the 1970s, [[computer terminal]]s were multiplexed onto large institutional [[mainframe computer]]s ([[centralized computing]] systems), which in many implementations sequentially polled the terminals to see whether any additional data was available or action was requested by the computer user. Later technology in interconnections were [[interrupt]] driven, and some of these used parallel data transfer technologies such as the [[IEEE 488]] standard. Generally, computer terminals were utilized on college properties in much the same places as ''[[desktop computer]]s'' or ''[[personal computer]]s'' are found today. In the earliest days of personal computers, many were in fact used as particularly smart terminals for time-sharing systems.

DTSS's creators wrote in 1968 that "any response time which averages more than 10 seconds destroys the illusion of having one's own computer".<ref name="dtss196810">{{cite journal | url=http://dtss.dartmouth.edu/sciencearticle/index.html | title=Dartmouth Time-Sharing |author1=Kemeny, John G. |author2=Kurtz, Thomas E. | journal=Science | date=11 October 1968 | volume=162 | issue=3850 | pages=223–228| doi=10.1126/science.162.3850.223 | pmid=5675464 | bibcode=1968Sci...162..223K | url-access=subscription }}</ref> Conversely, timesharing users thought that their terminal was the computer,<ref name="ncc1974">{{Cite web |url=http://dtss.dartmouth.edu/transcript.php |title=TRANSCRIPTS OF 1974 National Computer Conference Pioneer Day Session |website=Dartmouth Time Sharing System |publisher=Dartmouth College |year=1974}}</ref> and unless they received a bill for using the service, rarely thought about how others shared the computer's resources, such as when a large JOSS application caused [[paging]] for all users. The ''JOSS Newsletter'' often asked users to reduce storage usage.<ref name=marks197112>{{cite tech report
 |url=https://www.rand.org/content/dam/rand/pubs/reports/2008/R918.pdf
 |title=The JOSS Years: Reflections on an experiment
 |last=Marks |first=Shirley
 |date=December 1971
 |publisher=Rand
 |pages=32-33
 |access-date = 2019-06-19
}}</ref> Time-sharing was nonetheless an efficient way to share a large computer. {{asof|1972}} DTSS supported more than 100 simultaneous users. Although more than 1,000 of the 19,503 jobs the system completed on "a particularly busy day" required ten seconds or more of computer time, DTSS was able to handle the jobs because 78% of jobs needed one second or less of computer time. About 75% of 3,197 users used their terminal for 30 minutes or less, during which they used less than four seconds of computer time. A football simulation, among [[early mainframe games]] written for DTSS, used less than two seconds of computer time during the 15 minutes of real time for playing the game.<ref name="kemeny1972">{{Cite book |last=Kemeny |first=John G. |url=https://archive.org/details/mancomputer00keme/page/32/mode/2up?view=theater |title=Man and the Computer |publisher=Charles Scribner's Sons |year=1972 |location=New York |pages=32-37, 41-42 |isbn=9780684130095 |language=en-US |lccn=72-1176}}</ref> With the rise of microcomputing in the early 1980s, time-sharing became less significant, because individual microprocessors were sufficiently inexpensive that a single person could have all the [[CPU time]] dedicated solely to their needs, even when idle.

However, the Internet brought the general concept of time-sharing back into popularity. Expensive corporate server farms costing millions can host thousands of customers all sharing the same common resources. As with the early serial terminals, web sites operate primarily in bursts of activity followed by periods of idle time. This bursting nature permits the service to be used by many customers at once, usually with no perceptible communication delays, unless the servers start to get very busy.

===Time-sharing business===
'''Genesis'''

In the 1960s, several companies started providing time-sharing services as [[service bureau]]s. Early systems used [[Teletype Model 33]] KSR or ASR or Teletype Model 35 KSR or ASR machines in [[ASCII]] environments, and [[IBM Selectric typewriter]]-based terminals (especially the [[IBM 2741]]) with two different seven-bit codes.<ref>{{cite book
 |title=IBM 2741 Communication Terminal
 |publisher=IBM
 |page=12
 |url=http://www.textfiles.com/bitsavers/pdf/ibm/27xx/GA24-3415-3_2741_Data_Terminal_Aug72.pdf
 |access-date=2015-10-06
 |archive-date=2017-03-16
 |archive-url=https://web.archive.org/web/20170316041750/http://www.textfiles.com/bitsavers/pdf/ibm/27xx/GA24-3415-3_2741_Data_Terminal_Aug72.pdf
 |url-status=dead
 }}</ref> They would connect to the [[Centralized computing|central computer]] by [[dial-up]] Bell 103A modem or [[acoustic coupler|acoustically coupled]] [[modem]]s operating at 10&ndash;15 characters per second. Later terminals and modems supported 30&ndash;120 characters per second. The time-sharing system would provide a complete operating environment, including a variety of programming language processors, various software packages, file storage, bulk printing, and off-line storage. Users were charged rent for the terminal, a charge for hours of connect time, a charge for seconds of CPU time, and a charge for kilobyte-months of disk storage.

Common systems used for time-sharing included the [[SDS 940]], the [[PDP-10]], the [[IBM 360]], and the [[GE-600 series]]. Companies providing this service included [[GE]]'s [[GXS Inc.|GEISCO]], the [[IBM]] subsidiary The [[Service Bureau Corporation]], [[Tymnet|Tymshare]] (founded in 1966), [[National CSS]] (founded in 1967 and bought by Dun & Bradstreet in 1979), Dial Data (bought by Tymshare in 1968), [[Applied Logic Corporation|AL/COM]], [[Bolt, Beranek, and Newman]] (BBN) and [[Time Sharing Limited | Time Sharing Ltd.]] in the [[United Kingdom|UK]].<ref>Jeffrey R. Yost, ''Making IT Work: A History of the Computer Services Industry'', 2017, ISBN 0262342197 p. 158</ref> By 1968, there were 32 such service bureaus serving the US [[National Institutes of Health]] (NIH) alone.<ref>"Information Technology Corporate Histories Collection". Computer History Museum. Retrieved on 2013-11-29 from http://www.computerhistory.org/corphist/view.php?s=stories&id=136.</ref> The ''Auerbach Guide to Timesharing'' (1973) lists 125 different timesharing services using equipment from [[Burroughs Corporation|Burroughs]], [[Control Data Corporation|CDC]], [[Digital Equipment Corporation|DEC]], [[Hewlett-Packard|HP]], [[Honeywell]], [[IBM]], [[RCA]], [[Univac]], and [[Scientific Data Systems|XDS]].<ref name=Auerbach>{{cite book|title=Auerbach Guide to Time Sharing|year=1973|publisher=Auerbach Publishers, Inc.|url=http://bitsavers.trailing-edge.com/pdf/auerbach/GuideToTimesharing_Jan73.pdf|access-date=2013-11-29}}</ref><ref name="DECpro1">DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1</ref>

====Rise and fall====
In 1975, acting president of [[Prime Computer]] Ben F. Robelen told stockholders that "The biggest end-user market currently is time-sharing".<ref name="upton19750611">{{Cite magazine |last=Upton |first=Molly |date=1975-06-11 |title=Prime President Predicts '75 Orders On Target, Despite Recent Slowdown |url=https://books.google.com/books?id=79Vx176yQBEC&pg=PA35 |access-date=2024-10-23 |magazine=Computerworld |page=35}}</ref> For DEC, for a while the second largest computer company (after IBM), this was also true: Their [[PDP-10]] and IBM's [[IBM System/360 Model 67|360/67]]<ref>One Two-page IBM print ad was headlined "100 or more people can use IBM's new time-sharing computer at the same time." Originals were/are? on eBay</ref> were widely used<ref>p.1425, Encyclopedia of Computer Science, Litton Educational Publishing, Inc.</ref> by commercial timesharing services such as CompuServe, [[Embarq#History|On-Line Systems, Inc.]] (OLS), Rapidata and [[TELCOMP|Time Sharing Ltd.]]

The advent of the [[personal computer]] marked the beginning of the decline of time-sharing.{{Citation needed|date=November 2022|reason=There may other reasons.}} The economics were such that computer time went from being an expensive resource that had to be shared to being so cheap that computers could be left to sit idle for long periods in order to be available as needed.{{Citation needed|date=November 2022|reason=Some computers are still expensive resources.}}

=====Rapidata as an example=====
Although many time-sharing services simply closed, Rapidata<ref>https://groups.google.com/forum/#!topic/alt.folklore.computers/aE4TwORruB8 - "I worked for RapiData Timesharing for about a year circa 1969..."</ref><ref>someone else: "I worked there for almost 2 years 1977 to 1979." alt.folklore.computers/aE4TwORruB8/EdpKfFAlBncJ</ref> held on, and became part of [[McKesson Corporation|National Data Corporation]].<ref>{{Cite web |date=2023-05-26 |title=Stocks |url=https://www.bloomberg.com/markets/stocks |access-date=2023-05-26 |website=Bloomberg.com |language=en}}</ref> It was still of sufficient interest in 1982 to be the focus of "A User's Guide to Statistics Programs: The Rapidata Timesharing System".<ref>Bruce Bosworth, {{ISBN|978-089529-1-677}}</ref> Even as revenue fell by 66%<ref>''[[Computerworld]]'', Oct. 6, 1986, p.179, "Rapidata revenue was $11 million ... in 1986, down from ... ($31 million in 1982)."</ref> and National Data subsequently developed its own problems, attempts were made to keep this timesharing business going.<ref>Computerworld, Aug.25,1986, p.5,
"National Data Corp. said it is close to reaching an agreement with a buyer of its Rapidata timesharing division. In May, National Data said it would close down ..."</ref><ref>National Data Corp became NDC-Health Corp in 2001 (bizjournals.com/atlanta/stories/2001/10/29/daily25.html)</ref><ref>As for a place in history, Rapidata is listed in 'The AUERBACH Guide to Time Sharing (1973)' http://bitsavers.informatik.uni-stuttgart.de/pdf/auerbach/GuideToTimesharing_Jan73.pdf</ref>

=====UK=====
* [[Time Sharing Limited]] (TSL, 1969–1974) - launched using DEC systems. [[PERT]] was one of its popular offerings. TSL was acquired by [[Automatic Data Processing|ADP]] in 1974.
* OLS Computer Services (UK) Limited (1975–1980) - using HP & DEC systems.

===The computer utility===
Beginning in 1964, the [[Multics]] operating system<ref>{{cite web
    |website=BitSavers
    |url=http://www.bitsavers.org/pdf/honeywell/multics/AG92-06B_multicsCmds_Nov87.pdf
    |title=Multics Commands and Active Functions (AG92-06)
    |publisher=Honeywell Bull, Inc.
    |date=February 1985
    |access-date=January 10, 2021
    |archive-date=June 6, 2022
    |archive-url=https://web.archive.org/web/20220606144002/http://www.bitsavers.org/pdf/honeywell/multics/AG92-06B_multicsCmds_Nov87.pdf
    |url-status=dead
    }}</ref> was designed as a [[computing utility]], modeled on the electrical or telephone utilities. In the 1970s, [[Ted Nelson]]'s original "[[Project Xanadu|Xanadu]]" hypertext repository was envisioned as such a service. <!-- It seemed as the computer industry grew that no such consolidation of computing resources would occur as timesharing systems. In the 1990s the concept was, however, revived in somewhat modified form under the banner of [[cloud computing]].-->

===Security===
Time-sharing was the first time that multiple [[Process (computing)|processes]], owned by different users, were running on a single machine, and these processes could interfere with one another.<ref name=Silberschatz2010>{{cite book|last1=Silberschatz |first1=Abraham| last2=Galvin |first2=Peter|last3=Gagne |first3=Greg|title=Operating system concepts|year=2010|publisher= Wiley & Sons | location = Hoboken, N.J. | isbn = 978-0-470-23399-3 | edition = 8th | page = 591}}</ref> For example, one process might alter [[shared resource]]s which another process relied on, such as a variable stored in memory. When only one user was using the system, this would result in possibly wrong output - but with multiple users, this might mean that other users got to see information they were not meant to see.

To prevent this from happening, an operating system needed to enforce a set of policies that determined which [[Privilege (computing)|privileges]] each process had. For example, the operating system might deny access to a certain variable by a certain process.

The first international conference on computer security in London in 1971 was primarily driven by the time-sharing industry and its customers.<ref>{{cite thesis |last1=O'Neill |first1=Judy Elizabeth |title=The Evolution of Interactive Computing Through Time-sharing and Networking |date=1992 |oclc=1011609244 }}{{pn|date=February 2024}}</ref>

Time-sharing in the form of [[Shell account|shell accounts]] has been considered a risk.<ref>{{cite journal |last1=Toxen |first1=Bob |title=The Seven Deadly Sins of Linux Security: Avoid these common security risks like the devil. |journal=Queue |date=May 2007 |volume=5 |issue=4 |pages=38–47 |doi=10.1145/1255421.1255423 |doi-access=free |quote=Most recent vulnerabilities are not directly exploitable remotely on most systems. This means that most systems are not at risk for remote attack from the Internet. Many of the vulnerabilities may be taken advantage of by someone with a regular shell account on the system. }}</ref>

==Notable time-sharing systems==
{{See also|Time-sharing system evolution}}
Significant early timesharing systems:<ref name=Auerbach/>
* [[Allen-Babcock]] RUSH (Remote Users of Shared Hardware) Time-sharing System on [[IBM S/360]] hardware (1966)<ref>{{cite book |doi=10.1145/1465482.1465528 |chapter=A brief description of privacy measures in the RUSH time-sharing system |title=Proceedings of the April 18-20, 1967, spring joint computer conference on - AFIPS '67 (Spring) |date=1967 |last1=Babcock |first1=J. D. |page=301 }}</ref> → [[Tymshare]]
* [[AT&T Corporation|AT&T]] [[Bell Labs]] [[Unix]] (1971) → [[University of California, Berkeley|UC Berkeley]] [[Berkeley Software Distribution|BSD Unix]] (1977)
* [[BBN Technologies|BBN]] [[PDP-1]] Time-sharing System → [[Massachusetts General Hospital]] PDP-1D → [[MUMPS]]
* [[BBN Technologies|BBN]] [[TENEX (operating system)|TENEX]] → [[Digital Equipment Corporation|DEC]] [[TOPS-20]], Foonly FOONEX, MAXC OS at [[PARC (company)|PARC]], [[Stanford University|Stanford]] Low Overhead TimeSharing (LOTS), which ran [[TOPS-20]]
* [[Berkeley Timesharing System]] at [[University of California, Berkeley|UC Berkeley]] [[Project Genie]] → [[Scientific Data Systems]] [[SDS 940]] ([[Tymshare]], [[BBN Technologies|BBN]], [[Stanford Research Institute|SRI]], Community Memory) → BCC 500 → MAXC at PARC
* [[Burroughs Corporation|Burroughs]] Time-sharing [[Burroughs MCP|MCP]] → [[HP 3000]] MPE
* Cambridge Multiple Access System was developed for the [[Titan (1963 computer)|Titan]], the prototype [[Atlas (computer)|Atlas]] 2 computer built by [[Ferranti]] for the [[University of Cambridge]].<ref>{{Citation | last = Hartley | first = D. F. | author-link = David Hartley (computer scientist) | title = The Cambridge multiple-access system: user's reference manual | place = Cambridge | publisher = Cambridge Univ. Press | year = 1968 | isbn = 978-0901224002 }}</ref> This was the first time-sharing system developed outside the United States, and which influenced the later development of [[UNIX]].
* Compower Ltd., a wholly owned subsidiary of the National Coal Board (later British Coal Corporation) in the UK. Originally National Coal Board (NCB) Computer Services, it became Compower in 1973 providing computing and time-share services to internal NCB users and as a commercial service to external users. Sold to Philips C&P (Communications and Processing) in August 1994.
* [[CompuServe]], also branded as Compu-Serv, CIS.
* Compu-Time, Inc.,<ref name=Auerbach/> on [[Honeywell]] 400/4000, started in 1968 in Ft Lauderdale, Florida, moved to Daytona Beach in 1970.
* [[Control Data Corporation|CDC]] MACE, APEX → [[CDC Kronos|Kronos]] → [[NOS (operating system)|NOS]] → [[NOS/VE]]
* [[Dartmouth Time-Sharing System]] (DTSS) → GE Time-sharing → [[GEnie]]
* [[Digital Equipment Corporation|DEC]] [[PDP-6]] Time-sharing Monitor → [[TOPS-10]] → [[BBN Technologies|BBN]] TENEX → [[Digital Equipment Corporation|DEC]] [[TOPS-20]]
* [[Digital Equipment Corporation|DEC]] [[TSS/8]] → [[RSTS/E|RSTS-11]], [[RSX-11]] → [[OpenVMS]]
* [[KDF9|English Electric KDF9]] COTAN (Culham Online Task Activation Network)
* [[Hewlett-Packard|HP]] [[HP Time-Shared BASIC|2000 Time-Shared BASIC]]
* [[Hewlett-Packard|HP]] [[HP 3000|3000 series]]
* [[IBM]] [[List of IBM products#Services|CALL/360]], CALL/OS - using [[IBM System/360 Model 50]]
* [[IBM CP-40]] → [[CP-67]] → [[CP-370]] → [[CP/CMS]] → [[VM/CMS]]
* [[IBM]] [[Time Sharing Option|TSO]] for [[OS/MVT]] → for [[OS/VS2 (SVS)|OS/VS2]] → for [[MVS]] → for [[z/OS]]
* [[IBM]] [[TSS/360]] → TSS/370
* [[ICT 1900 series]] [[GEORGE 3]] MOP (Multiple Online Programming)
* International Timesharing Corporation on dual [[CDC 3000|CDC 3300]] systems.<ref name=Auerbach/>
* Linux: see how it evolved from MIT CTSS
* [[Massachusetts Institute of Technology|MIT]] [[Compatible Time-Sharing System|CTSS]] → [[MULTICS]] (MIT / [[General Electric|GE]] / Bell Labs) → [[Unix]] → [[Linux]]
* [[Massachusetts Institute of Technology|MIT]] Time-sharing System for the [[Digital Equipment Corporation|DEC]] [[PDP-1]] → [[Incompatible Timesharing System|ITS]]
* [[McGill University]] MUSIC → IBM [[MUSIC/SP]]
* [[Michigan Terminal System]], on the [[IBM System/360 Model 67|IBM S/360-67]], [[S/370]], and successors.
* [[Michigan State University]] [[CDC SCOPE (software)|CDC SCOPE]]/HUSTLER System
* [[National CSS]] [[VP/CSS]], on [[IBM 360]] series; originally based on IBM's [[CP/CMS]].
* [[Oregon State University]] OS-3, on [[CDC 3000]] series.
* [[Prime Computer]] [[PRIMOS]]
* [[RAND]] [[JOSS]] → JOSS-2 → JOSS-3
* [[RCA]] [[Time Sharing Operating System|TSOS]] → [[UNIVAC|Univac]] / [[Unisys]] VMOS → [[VS/9]]
* [[Service in Informatics and Analysis|Service in Informatics and Analysis (SIA)]], on [[CDC 6600]] [[CDC Kronos|Kronos]].
* [[System Development Corporation]] Time-sharing System, on the [[AN/FSQ-32]].
* [[Stanford University|Stanford]] [[ORVYL and WYLBUR]], on [[IBM System/360 Model 67|IBM S/360-67]].
* [[Stanford University|Stanford]] [[PDP-1]] Time-sharing System → [[Stanford Artificial Intelligence Laboratory|SAIL]] → [[WAITS]]
* [[Time Sharing Limited | Time Sharing Ltd.]] (TSL)<ref>[http://www.jamesmiller.com/timesharing001.html "Time Sharing"], James Miller. Retrieved 30 November 2013.</ref> on [[Digital Equipment Corporation|DEC]] [[PDP-10]] systems → [[Automatic Data Processing]] (ADP), first commercial time-sharing system in Europe and first dual (fault tolerant) time-sharing system.
* [[OS/VS1#TONE for VS1|Tone]] (TSO-like, for [[OS/VS1|VS1]]), a non-IBM Time-sharing product, marketed by Tone Software Co; TSO required VS2.
* [[Tymshare]] SDS-940 → Tymcom X → Tymcom XX
* [[Unisys]]/[[UNIVAC 1108]] [[EXEC 8]] → OS 1100 → [[OS 2200]]
* [[University of California, Berkeley|UC Berkeley]] CAL-TSS, on [[CDC 6000 series|CDC 6400]].
* [[Scientific Data Systems|XDS]] [[Universal Time-Sharing System|UTS]] → [[CP-V operating system|CP-V]] → [[Honeywell CP-6]]

==See also==
* [[Cloud computing]]
* ''[[Computer Networks: The Heralds of Resource Sharing|The Heralds of Resource Sharing]]'', a 1972 film.
* [[History of CP/CMS]], IBM's virtual machine operating system (CP) that supported time-sharing (CMS).
* [[IBM M44/44X]], an experimental computer system based on an [[IBM 7044]] used to simulate multiple virtual machines.
* [[IBM System/360 Model 67]], the only [[IBM S/360|IBM S/360 series]] mainframe to support virtual memory.
* [[Multiseat configuration]], multiple users on a single [[personal computer]].
* [[Project MAC]], a [[DARPA]] funded project at [[MIT]] famous for groundbreaking research in [[operating system]]s, [[artificial intelligence]], and the [[theory of computation]].
* [[TELCOMP]], an interactive, conversational programming language based on [[JOSS]], developed by [[BBN Technologies|BBN]] in 1964.
* [[Timeline of operating systems]]
* [[VAX]] (Virtual Address eXtension), a computer architecture and [[VAX-11|family of computers]] developed by [[Digital Equipment Corporation|DEC]].
* [[Utility computing]]
* [[Virtual memory]]
* [[Time-sharing system evolution]]

==References==
{{Reflist}}

==Further reading==
* [[Ted Nelson|Nelson, Theodor]] (1974). ''Computer Lib: You Can and Must Understand Computers Now''; [[Computer Lib / Dream Machines|''Dream Machines'']]: "New Freedoms Through Computer Screens&mdash; A Minority Report". Self-published. {{ISBN|0-89347-002-3}}. pp.&nbsp;56–57.
*{{cite journal|first=Edward|last=Fredkin|title=The Time Sharing of Computers|journal=Computers and Automation|date=Nov 1963|volume=XII|issue=11|pages=12–13, 16–20|url=http://www.bitsavers.org/magazines/Computers_And_Automation/196311.pdf}}: <cite>"The author relates a short history of time-sharing, the initial time-sharing experiments, the modifications of existing computers and those designed specifically for time-sharing, [[project MAC]], significant features of the system, services, languages, programs, scope displays and light pens, and intercommunication.</cite><ref>{{cite book |last1=Allen |first1=Ruth |last2=(U.S.) |first2=National Library of Medicine |title=An Annotated Bibliography of Biomedical Computer Applications |date=1969 |publisher=National Library of Medicine |location=70 |url=https://books.google.com/books?id=AKhPv9YWTeQC&q=%22TIME+SHARING+OF+COMPUTERS%22+fredkin |language=en}}</ref>

== External links ==
* {{cite thesis |last1=Alexander |first1=Michael T. |title=Time Sharing Supervisor Programs |date=May 1971 |hdl=2027.42/79614 }}
* [http://www.frankston.com/public/?name=TR128 "The Computer Utility As A Marketplace For Computer Services"], [[Bob Frankston|Robert Frankston]]'s MIT Master's Thesis, 1973.
* [https://web.archive.org/web/20160521092337/http://www.cio.com.au/article/325323/cio_blast_from_past_40_years_multics_1969-2009 "40 years of Multics, 1969-2009"], an interview with Professor [[Fernando J. Corbató]] on the history of [[Multics]] and origins of time-sharing, 2009.
* [http://www.computerhistory.org/revolution/mainframe-computers/7/178 "Mainframe Computers: The Virtues of Sharing"], Revolution: The First 2000 Years of Computing, Computer History Museum Exhibition, January 2011.
* [http://www.computerhistory.org/revolution/mainframe-computers/7/181 "Mainframe Computers: Timesharing as a Business"], Revolution: The First 2000 Years of Computing, Computer History Museum Exhibition, January 2011.

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[[Category:Operating system technology]]
[[Category:Computer systems]]