Editing Compatible Time-Sharing System (section)

==History==
[[John Backus]] said in the 1954 summer session at [[Massachusetts Institute of Technology|MIT]] that "By time sharing, a big computer could be used as several small ones; there would need to be a reading station for each user".<ref name="jbackus">{{cite book |last=Backus |first=John |url=https://bitsavers.org/pdf/mit/whirlwind/summer_session_1954/Digital_Computers_Advanced_Coding_Techniques_Summer_1954.pdf |title=Digital Computer Advanced Coding Techniques |publisher=MIT |date=1954 |pages=16{{hyp}}2–16{{hyp}}3}} The first known description of computer time-sharing.</ref> Computers at that time, like [[IBM 704]], were not powerful enough to implement such system, but at the end of 1958, MIT's Computation Center nevertheless added a typewriter input to its 704 with the intent that a programmer or operator could "obtain additional answers from the machine on a time-sharing basis with other programs using the machine simultaneously".<ref>{{cite report |url=https://archive.org/details/cooperating-colleges-progress-4 |title=Progress Report Number 4 of the Research and Educational Activities in Machine Computation by the Cooperating Colleges of New England |date=December 1958}}</ref>

In June 1959, [[Christopher Strachey]] published a paper "Time Sharing in Large Fast Computers" at the [[International Federation for Information Processing#History|UNESCO Information Processing Conference]] in Paris, where he envisaged a programmer [[debugging]] a program at a console (like a [[Teleprinter|teletype]]) connected to the computer, while another program was running in the computer at the same time.<ref name="ctsspg63">{{cite book |author1=F. J. Corbató |author2=M. M. Daggett |author3=R. C. Daley |author4=R. J. Creasy |author5=J. D. Hellwig |author6=R. H. Orenstein |author7=L. K. Korn |url=http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide.pdf |title=The Compatible Time-Sharing System A Programmer's Guide |publisher=MIT Press |date=1963 |isbn=978-0-262-03008-3 |access-date=2007-02-04 |archive-date=2012-05-27 |archive-url=https://web.archive.org/web/20120527174321/http://www.bitsavers.org/pdf/mit/ctss/CTSS_ProgrammersGuide.pdf |url-status=live }} Describe the system and its commands</ref><ref name="mccarthyts">{{cite web |author=John McCarthy |url=https://www-formal.stanford.edu/jmc/history/timesharing/timesharing.html |title=Reminiscences on the History of Time Sharing |website=Stanford University |date=1983}}</ref> Debugging programs was an important problem at that time, because with batch processing, it then often took a day from submitting a changed code, to getting the results. [[John McCarthy (computer scientist)|John McCarthy]] wrote a memo about that at MIT, after which a preliminary study committee and a working committee were established at MIT, to develop time sharing. The committees envisaged many users using the computer at the same time, decided the details of implementing such system at MIT, and started the development of the system.

===Experimental Time Sharing System===
By July, 1961<ref>{{cite report |url=https://archive.org/details/cooperating-colleges-progress-9 |title=Progress Report Number 9 of the Research and Educational Activities in Machine Computation by the Cooperating Colleges of New England |date=July 1961}}</ref> a few time sharing commands had become operational on the Computation Center's IBM 709, and in November 1961, [[Fernando J. Corbató]] demonstrated at MIT what was called the ''Experimental Time-Sharing System''. On May 3, 1962, F. J. Corbató, M. M. Daggett and R. C. Daley published a paper about that system at the [[Joint Computer Conference|Spring Joint Computer Conference]].<ref name="etss">{{cite web |url=http://larch-www.lcs.mit.edu:8001/~corbato/sjcc62/ |title=An Experimental Time-Sharing System |last1=Corbató |first1=Fernando J. |last2=Merwin Daggett |first2=Marjorie |last3=Daley |first3=Robert C. |date=May 3, 1962 |access-date=February 25, 2022 |archive-url=https://web.archive.org/web/20090906104446/http://larch-www.lcs.mit.edu:8001/~corbato/sjcc62/ |archive-date=September 6, 2009 |url-status=live}}</ref> "[M]ajor portions of [the CTSS system were largely prepared by]: Mrs. Marjorie M. Daggett, Mr. Robert Daley, Mr. Robert Creasy, Mrs. Jessica Hellwig, Mr. Richard Orenstein, and Professor F. J. Corbató".<ref name="CorbatVii">Corbató, p. vii</ref>

The system used an [[IBM 7090]], modified by [[Herbert M. Teager]], with added 3 [[Friden Flexowriter|Flexowriters]] for user consoles, and maybe a [[Programmable interval timer|timer]]. Each of the 3 users had two [[IBM 729|tape units]], one for the user's file directory, and one for dumping the core (program in memory). There was also one tape unit for the system commands, there were no disk drives. The [[Magnetic-core memory|memory]] was 27 k words (36-bit words) for users, and 5 k words for the supervisor (operating system). The input from the consoles was written to the buffers in the supervisor, by [[interrupt]]s, and when a [[Carriage return|return character]] was received, the control was given to the supervisor, which dumped the running code to the tape and decided what to run next. The console commands implemented at the time were ''login, logout, input, edit, fap, mad, madtrn, load, use, start, skippm, listf, printf, xdump'' and ''xundump''.{{citation needed |reason=CTSS command names are limited to six characters so how could xundump be a command? |date=February 2022}}

This became the initial version of the Compatible Time-Sharing System. This was apparently the first ever public demonstration of [[time-sharing]]; there are other claims, but they refer to special-purpose systems, or with no known papers published. The "compatibility" of CTSS was with background jobs run on the same computer, which generally used more of the compute resources than the time-sharing functions.