Editing EDSAC

{{Short description|1940s–1950s British computer}}
{{distinguish|EDSA|ESDAC}}
{{Use dmy dates|date=April 2016}}
{{Infobox information appliance
| name = Electronic Delay Storage Automatic Calculator (EDSAC)
| title =
| logo =
| image = EDSAC (19).jpg
| caption = EDSAC I in June 1948
| developer = [[Maurice Wilkes]] and his team at the [[University of Cambridge Mathematical Laboratory]]
| manufacturer = [[University of Cambridge]]
| family =
| type =
| generation = 1
| releasedate = {{Start date and age|1949|05|06|df=yes}}<!-- {{Start date|YYYY|MM|DD}} -->
| lifespan = 1949–1958
| price =
| discontinued = yes
| unitssold =
| unitsshipped = 1
| media =
| os = None
| power = 11 [[Kilowatt|kW]]
| soc =
| cpu = [[derating|Derated]] [[vacuum tube|thermionic valves]]
| memory = 512 17-bit words, upgraded in 1952 to 1024 17-bit words
| RAMtype = [[Delay-line memory|temperature-stabilized mercury delay lines]]
| storage =
| memory card =
| display = [[Teleprinter]]
| graphics =
| sound =
| input = five-hole [[punched tape]]
| controllers =
| camera =
| touchpad =
| connectivity =
| currentfw =
| platform =
| service =
| dimensions =
| weight =
| topgame =
| compatibility = None
| predecessor =
| successor = [[EDSAC 2]] and [[LEO (computer)|LEO I]]
| related = [[EDVAC]]
| website =
}}
The '''Electronic Delay Storage Automatic Calculator''' ('''EDSAC''') was an early British computer.<ref>{{cite journal |author=Wilkes, W. V. |author-link=Maurice Wilkes |author2=Renwick, W. |title=The EDSAC (Electronic delay storage automatic calculator) |journal=Math. Comp. |year=1950 |volume=4 |issue=30 |pages=61–65 |url=https://www.ams.org/journals/mcom/1950-04-030/S0025-5718-1950-0037589-7/ |doi=10.1090/s0025-5718-1950-0037589-7 |doi-access=free}}</ref> Inspired by [[John von Neumann]]'s seminal ''[[First Draft of a Report on the EDVAC]]'', the machine was constructed by [[Maurice Wilkes]] and his team at the [[University of Cambridge Mathematical Laboratory]] in England to provide a service to the university. EDSAC was the second electronic digital [[stored-program computer]], after the [[Manchester Mark 1]], to go into regular service.<ref>The 1948 [[Manchester Baby]] computer predated EDSAC as a [[stored-program computer]], but was built largely as a test bed for the [[Williams tube]] and not as a machine for general use. See [http://www.cl.cam.ac.uk/conference/EDSAC99/history.html "A brief informal history of the Computer Laboratory"]. However, the Baby was developed into a practically useful successor, the [[Manchester Mark&nbsp;1]] of 1949, which was available for general use by other university departments and Ferranti in April 1949, despite still being under development; EDSAC first ran in May 1949, while also still being under development. {{cite web |url=http://www.computer50.org/mark1/MM1.html |title=50th Anniversary of the Manchester Baby computer |access-date=2014-01-05 |url-status=dead |archive-url=https://web.archive.org/web/20140209155638/http://www.computer50.org/mark1/MM1.html |archive-date=9 February 2014 |df=dmy-all }}</ref>

Later the project was supported by [[J. Lyons and Co.|J. Lyons & Co. Ltd.]], intending to develop a commercially applied computer and resulting in Lyons' development of the [[LEO (computer)|LEO&nbsp;I]], based on the EDSAC design. Work on EDSAC started during 1947,<ref>{{cite journal |url=https://ieeexplore.ieee.org/document/560726 |author=Wilkes, M. V. |title=Arithmetic on the EDSAC |journal= IEEE Annals of the History of Computing|volume=19 |issue=1 |pages=13–15 |year=1997 |doi=10.1109/85.560726|url-access=subscription }}</ref> and it ran its first programs on 6&nbsp;May 1949, when it calculated a table of [[square number]]s<ref>{{cite journal |title=Pioneer computer to be rebuilt |journal=Cam |volume=62 |date=2011 |page=5}} To be precise, EDSAC's first program printed a list of the [[square number|squares]] of the [[integer (computer science)|integers]] from 0 to 99 inclusive.</ref> and a list of [[prime number]]s.<ref>{{Cite book |url=https://books.google.com/books?id=AoWrCAAAQBAJ&q=EDSAC%201948&pg=PA29 |title=Dependable and Historic Computing: Essays Dedicated to Brian Randell on the Occasion of his 75th Birthday |last1=Jones |first1=Cliff B. |last2=Lloyd |first2=John L. |date=2012-01-24 |publisher=Springer |isbn=9783642245411 |pages=29 |language=en}}</ref><ref>{{Cite journal |date=1950-01-01 |others=Other early computational problems run on EDSAC; some specifications of the computer |title=9. The EDSAC, Cambridge University, England |url=https://apps.dtic.mil/sti/citations/AD0694596 |archive-url=https://web.archive.org/web/20210311004157/http://www.dtic.mil/docs/citations/AD0694596 |url-status=live |archive-date=11 March 2021 |journal=Digital Computer Newsletter |language=en |volume=2 |issue=1 |pages=3}}</ref> EDSAC was finally shut down on 11&nbsp;July 1958, having been superseded by [[EDSAC&nbsp;2]], which remained in use until 1965.<ref>{{citation |url=http://www.cl.cam.ac.uk/events/EDSAC99/booklet.pdf |title=EDSAC 99: 15–16 April 1999 |publisher=University of Cambridge Computer Laboratory |date=6 May 1999 |access-date=2013-06-29 |pages=68, 69}}.</ref>

==Project and plan==
The conception of the EDSAC I can be traced back to 1945, during early planning of the [[EDVAC]]. In June of that year, [[John von Neumann]] wrote his [[First Draft of a Report on the EDVAC]] while taking on a consulting role while [[J. Presper Eckert]] and [[John Mauchly]] were the designers. The document described the concept of a stored-program computer, where both the program and data are stored in the same memory, which is now known as the [[Von Neumann architecture]]; it briefly explains the idea that computer instructions, or the program, could be stored in the same memory as the data, allowing for flexibility and automation in computation.

Later in August 1946, when Wilkes participated in the final weeks of the [[Moore School Lectures]], he was exposed to the principles of the [[ENIAC]] – Eckert and Mauchly's previous invention – and their proposed next project, the EDVAC.<ref name="EDSAC DEV">{{cite news|url=https://www.bbc.com/news/technology-11875821|date=November 30, 2010|title=Father of British computing Sir Maurice Wilkes dies|work=[[BBC News]]|access-date=March 16, 2025}}</ref> He proposed the concept of microprogramming, a system that simplifies the logical design of computers, which later became widely adopted in the industry. Using the knowledge he gathered about the EDVAC's working concept in the lectures, he began development of the EDSAC I in October of that year.<ref>{{cite web|url=https://www.cl.cam.ac.uk/archive/mvw1/short-biography.html|title=Maurice V. Wilkes: Shortly Biography|work=[[Department of Computer Science and Technology, University of Cambridge|Department of Computer Science and Technology]]|access-date=March 16, 2025}}</ref><ref>{{cite web|url=https://history.computer.org/pioneers/wilkes.html|title=Maurice Vincent Wilkes - Computer Pioneers|work=[[IEEE Computer Society]]|access-date=March 16, 2025}}</ref>

==Technical overview==

===Physical components===
[[File:EDSAC (5).jpg|thumb|9-inch tubes used for monitoring]]
[[File:EDSAC (20).jpg|thumb|William Renwick with 5-hole tape reader and Creed teleprinter]]
As soon as EDSAC was operational, it began serving the university's research needs. It used [[delay-line memory|mercury delay lines]] for memory and [[derating|derated]] [[vacuum tube]]s for logic. Power consumption was 11&nbsp;[[Kilowatt|kW]] of electricity.<ref>{{cite web| url=https://www.youtube.com/watch?v=lXJ-tYqPARg | title=EDSAC Simulator | publisher=Computerphile | work=[[YouTube]] | date=21 February 2018 }}</ref><ref name="autogeneratedcl" /> Cycle time was 1.5&nbsp;ms for all ordinary instructions, 6&nbsp;ms for multiplication. Input was via five-hole [[punched tape]], and output was via a [[teleprinter]].

Initially, registers were limited to an [[Accumulator (computing)|accumulator]] and a multiplier register. In 1953, [[David Wheeler (computer scientist)|David Wheeler]], returning from a stay at the [[University of Illinois at Urbana–Champaign|University of Illinois]], designed an [[index register]] as an extension to the original EDSAC hardware.

A magnetic-tape drive was added in 1952 but never worked sufficiently well to be of real use.<ref name="autogeneratedcl">{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/statistics.html | title=Some EDSAC statistics | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref>

Until 1952, the available main memory (instructions and data) was only 512 18-bit words, and there was no backing store.<ref>{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/reminiscences/#EDSAC%201%20applications | title=EDSAC 1 applications | work=EDSAC 1 and after – a compilation of personal reminiscences | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref> The delay lines (or "tanks") were arranged in two batteries providing 512 words each. The second battery came into operation in 1952.<ref name="autogeneratedcl"/>

The full 1024-word delay-line store was not available until 1955 or early 1956,<ref>{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/reminiscences/#EDSAC%201%20maintenance | title=EDSAC 1 maintenance | work=EDSAC 1 and after – a compilation of personal reminiscences | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref> limiting programs to about 800 words until then.

John Lindley (diploma student 1958–1959) mentioned "the incredible difficulty we had ever to produce a single correct piece of paper tape with the crude and unreliable home-made punching, printing and verifying gear available in the late 50s".<ref>{{cite web| url=http://www.cl.cam.ac.uk/events/EDSAC99/reminiscences/#EDSAC%202%20operating | title=EDSAC 1 operating | work=EDSAC 1 and after – a compilation of personal reminiscences | publisher=[[University of Cambridge Computer Laboratory]] | location=UK }}</ref>

===Memory and instructions===
[[File:EDSAC (9).jpg|thumb|upright|[[Maurice Wilkes]] inspecting the mercury [[delay-line memory|delay line]] of the EDSAC in construction]]
[[File:EDSAC (12).jpg|thumb|Maurice Wilkes and Bill Renwick in front of the complete EDSAC]]
The EDSAC's main memory consisted of 1024 locations, though only 512 locations were initially installed. Each contained 18&nbsp;bits, but the topmost bit was always unavailable due to timing problems, so only 17&nbsp;bits were used. An instruction consisted of a five-bit instruction code, one spare bit, a 10-bit operand (usually a memory address), and one length bit to control whether the instruction used a 17-bit or a 35-bit operand (two consecutive words, [[Endianness|little-endian]]). All instruction codes were by design represented by one mnemonic letter, so that the ''Add'' instruction, for example, used the EDSAC character code for the letter&nbsp;A.

Internally, the EDSAC used [[two's complement]] [[Binary number|binary]] numbers. Numbers were either 17&nbsp;bits (one word) or 35&nbsp;bits (two words) long. Unusually, the [[Binary multiplier|multiplier]] was designed to treat numbers as [[fixed-point arithmetic|fixed-point]] fractions in the range −1 ≤ ''x'' &lt; 1, i.e. the binary point was immediately to the right of the sign. The [[Accumulator (computing)|accumulator]] could hold 71&nbsp;bits, including the sign, allowing two long (35-bit) numbers to be multiplied without losing any precision.

The instructions available were:
* Add
* Subtract
* Multiply-and-add
* AND-and-add (called "Collate")
* Shift left
* Arithmetic shift right
* Load multiplier register
* Store (and optionally clear) accumulator
* Conditional goto
* Read input tape
* Print character
* Round accumulator
* No-op
* Stop
There was no division instruction (but various division subroutines were supplied) and no way to directly load a number into the accumulator (a "Store and zero accumulator" instruction followed by an "Add" instruction were necessary for this). There was no unconditional jump instruction, nor was there a procedure call instruction&nbsp;– it had not yet been invented.

[[Maurice Wilkes]] discussed relative addressing modes for the EDSAC in a paper published in 1953. He was making the proposals to facilitate the use of [[subroutine]]s.<ref>Proceedings of the Cambridge Philosophical Society, Vol.&nbsp;49, Pt.&nbsp;1, p.&nbsp;84–89.</ref>

===System software===
The ''initial orders'' were hard-wired on a set of [[Stepping switch|uniselector switches]] and loaded into the low words of memory at startup. By May 1949, the initial orders provided a primitive relocating [[Assembly language assembler|assembler]] taking advantage of the mnemonic design described above, all in 31 words. This was the world's first assembler, and arguably the start of the global software industry. There is a simulation of EDSAC available, and a full description of the initial orders and first programs.<ref>{{Cite web| title=Edsac Simulator | url=https://www.dcs.warwick.ac.uk/~edsac/ | access-date=2023-05-24 | website=dcs.warwick.ac.uk | publisher=[[University of Warwick]] | location=UK }}</ref>

The first calculation done by EDSAC was a program run on 6&nbsp;May 1949 to compute [[square number]]s.<ref name=":0">{{Cite web |url=http://www.computinghistory.org.uk/det/5484/EDSAC-performed-its-first-calculations/ |title=EDSAC performed its first calculations |website=Computing History |access-date=2018-11-23 |archive-date=26 February 2021 |archive-url=https://web.archive.org/web/20210226185505/http://www.computinghistory.org.uk/det/5484/EDSAC-performed-its-first-calculations/ |url-status=dead }}</ref> The program was written by [[Beatrice Worsley]], who had travelled from Canada to study the machine.<ref>{{Cite web |url=https://www.thecanadianencyclopedia.ca/en/article/beatrice-worsley |title=Beatrice Worsley |last=Raymond |first=Katrine |date=25 October 2017 |website=The Canadian Encyclopedia |language=en |archive-url=https://web.archive.org/web/20180113171457/http://www.thecanadianencyclopedia.ca/en/article/beatrice-worsley/ |archive-date=13 January 2018 |access-date=2018-11-23}}</ref><ref name=":0" />

The machine was used by other members of the university to solve real problems, and many early techniques were developed that are now included in operating systems.

Users prepared their programs by punching them (in assembler) onto a paper tape. They soon became good at being able to hold the paper tape up to the light and read back the codes. When a program was ready, it was hung on a length of line strung up near the paper-tape reader. The machine operators, who were present during the day, selected the next tape from the line and loaded it into EDSAC. This is of course well known today as job queues. If it printed something, then the tape and the printout were returned to the user, otherwise they were informed at which memory location it had stopped. Debuggers were some time away, but a [[cathode-ray tube]] screen could be set to display the contents of a particular piece of memory. This was used to see whether a number was converging, for example. A loudspeaker was connected to the accumulator's sign bit; experienced users knew healthy and unhealthy sounds of programs, particularly programs "hung" in a loop.

After office hours certain "authorised users" were allowed to run the machine for themselves, which went on late into the night until a valve blew – which usually happened according to one such user.<ref>Professor David Barron, Emeritus Professor of the University of Southampton at a Cambridge Computer Lab seminar to mark the 60th anniversary 6&nbsp;May 2009.</ref> This is alluded to by [[Fred Hoyle]] in his novel ''[[The Black Cloud]]''

===Programming technique===
[[File:EDSAC (23).jpg|thumb|EDSAC monitoring desk<ref>Description of three displays (counter, memory and sequence control): {{cite news |title=Two new EDSAC videos: EDSAC's VDU screens |url=http://www.tnmoc.org/news/edsac/two-new-edsac-videos |work=The National Museum of Computing |date=11 December 2015 |language=en}}</ref>]]
The early programmers had to make use of techniques frowned upon today—in particular, the use of [[self-modifying code]]. As there was no index register until much later, the only way of accessing an array was to alter which memory location a particular instruction was referencing.

[[David Wheeler (computer scientist)|David Wheeler]], who earned the world's first Computer Science PhD working on the project, is credited with inventing the concept of a subroutine. Users wrote programs that called a routine by jumping to the start of the subroutine with the [[Return statement|return address]] (i.e. the location-plus-one of the jump itself) in the accumulator (a [[Wheeler Jump]]). By convention the subroutine expected this, and the first thing it did was to modify its concluding jump instruction to that return address. Multiple and nested subroutines could be called so long as the user knew the length of each one in order to calculate the location to jump to; [[Recursion (computer science)|recursive calls]] were forbidden. The user then copied the code for the subroutine from a master tape onto their own tape following the end of their own program. (However, [[Alan Turing]] discussed subroutines in a paper of 1945 on design proposals for the NPL [[Automatic Computing Engine|ACE]], going so far as to invent the concept of a return-address stack, which would have allowed recursion.{{sfn|Turing|1945|loc=reprinted in Copeland (2005), p. 383}})

The lack of an index register also posed a problem to the writer of a subroutine in that they could not know in advance where in memory the subroutine would be loaded, and therefore they could not know how to address any regions of the code that were used for storage of data (so-called "pseudo-orders"). This was solved by use of an initial input routine, which was responsible for loading subroutines from punched tape into memory. On loading a subroutine, it would note the start location and increment internal memory references as required. Thus, as Wilkes wrote, "the code used to represent orders outside the machine differs from that used inside, the differences being dictated by the different requirements of the programmer on the one hand, and of the control circuits of the machine on the other".<ref>{{cite book |last1=Wilkes |first1=M. V. |title=Automatic digital computers |date=1956 |publisher=Methuen |location=London |pages=93–95}}</ref>

EDSAC's programmers used special techniques to make best use of the limited available memory. For example, at the point of loading a subroutine from punched tape into memory, it might happen that a particular constant would have to be calculated, a constant that would not subsequently need recalculation. In this situation, the constant would be calculated in an "interlude". The code required to calculate the constant would be supplied along with the full subroutine. After the initial input routine had loaded the calculation-code, it would transfer control to this code. Once the constant had been calculated and written into memory, control would return to the initial input routine, which would continue to write the remainder of the subroutine into memory, but first adjusting its starting point so as to overwrite the code that had calculated the constant. This allowed quite complicated adjustments to be made to a general-purpose subroutine without making its final footprint in memory any larger than had it been tailored to a specific circumstance.<ref>{{cite book |last1=Wilkes |first1=M. V. |title=Automatic digital computers |date=1956 |publisher=Methuen |location=London |pages=108–109}}</ref>

===Application software===
The subroutine concept led to the availability of a substantial subroutine library. By 1951, 87 subroutines in the following categories were available for general use: [[floating-point arithmetic]]; arithmetic operations on [[complex number]]s; checking; division; [[exponentiation]]; routines relating to functions; [[differential equation]]s; special functions; [[power series]]; [[logarithm]]s; miscellaneous; print and layout; [[Numerical integration|quadrature]]; read (input); ''n''th root; [[trigonometric functions]]; counting operations (simulating [[do while loop|repeat until loops]], [[while loop]]s and [[for loop]]s); [[probability vector|vectors]]; and [[matrix (mathematics)|matrices]].

The first [[assembly language]] appeared for the EDSAC, and inspired several other assembly languages:
{| class="wikitable"
|-
! Year
! Name
! Chief developer, company
|-
| 1951
| Regional Assembly Language
| [[Maurice Wilkes]]
|-
| 1951
| [[Whirlwind (computer)|Whirlwind]] assembler
| Charles Adams and Jack Gilmore at [[Massachusetts Institute of Technology|MIT]]
|-
| 1951
| Rochester assembler
| [[Nathaniel Rochester (computer scientist)|Nat Rochester]]
|}

==Applications of EDSAC==
EDSAC was designed specifically to form part of the Mathematical Laboratory's support service for calculation.<ref>{{Citation |last= Goddard |first= Jonathan |title= 70 years since the first computer designed for practical everyday use |publisher= Department of Computer Science and Technology, [[University of Cambridge]] |date= 3 May 2019 |url= https://www.cst.cam.ac.uk/news/70-years-first-computer-designed-practical-everyday-use }}</ref> [[Ronald Fisher]], in collaboration with Wilkes and Wheeler, used EDSAC to solve a differential equation relating to gene frequencies; this represented the first application of a computer to research in [[biology]].<ref>{{cite journal| last = Fisher| first = R.A.| author-link = Ronald Fisher| title = Gene Frequencies in a Cline Determined by Selection and Diffusion| journal = Biometrics| volume = 6| issue = 4| pages = 353–361| url = https://www.jstor.org/stable/3001780}}</ref><ref>{{Cite web |last=Livesey |first=James |date=2019-01-08 |title=The EDSAC and Computing in Cambridge |url=https://www.whipplemuseum.cam.ac.uk/explore-whipple-collections/calculating-devices/edsac-and-computing-cambridge |url-status=live |archive-url=https://web.archive.org/web/20250114144113/https://www.whipplemuseum.cam.ac.uk/explore-whipple-collections/calculating-devices/edsac-and-computing-cambridge |archive-date=2025-01-14 |access-date=2025-01-28 |website=www.whipplemuseum.cam.ac.uk |language=en}}</ref> In 1951, Miller and Wheeler used the machine to discover a 79-digit prime<ref>[http://primes.utm.edu/notes/by_year.html Caldwell – largest known primes by year]. One reference gives Miller, J. C. P. "Larger Prime Numbers" (1951) ''Nature'' 168(4280):838, but the [http://www.nature.com/nature/journal/v168/n4280/abs/168838b0.html abstract] does not mention it.</ref>&nbsp;– the [[Largest known prime|largest known]] at the time.

The winners of three Nobel Prizes{{snd}} [[John Kendrew]] and [[Max Perutz]] (Chemistry, 1962), [[Andrew Huxley]] (Medicine, 1963) and [[Martin Ryle]] (Physics, 1974){{snd}} benefitted from EDSAC's revolutionary computing power. In their acceptance prize speeches, each acknowledged the role that EDSAC had played in their research.

In the early 1960s [[Peter Swinnerton-Dyer]] used the EDSAC computer to calculate the number of points modulo ''p'' (denoted by ''N<sub>p</sub>'') for a large number of primes ''p'' on elliptic curves whose rank was known. Based on these numerical results, {{harvtxt|Birch|Swinnerton-Dyer|1965}} conjectured that ''N<sub>p</sub>'' for a curve ''E'' with rank ''r'' obeys an asymptotic law, the [[Birch and Swinnerton-Dyer conjecture]], considered one of the [[Millennium Prize Problems|top unsolved problems in mathematics]] as of 2024.

{{blockquote
|The "brain" [computer] may one day come down to our level [of the common people] and help with our income-tax and book-keeping calculations. But this is speculation and there is no sign of it so far.
|British newspaper ''The Star'' in a June 1949 news article about the EDSAC computer, long before the era of the personal computers.<ref>{{Cite web| url=http://www.dcs.warwick.ac.uk/~edsac/Software/EdsacTG.pdf | title=Archived copy | website=dcs.warwick.ac.uk | publisher=[[University of Warwick]] | location=UK | access-date=18 November 2016 |archive-url=https://web.archive.org/web/20151222132057/http://www.dcs.warwick.ac.uk/~edsac/Software/EdsacTG.pdf |archive-date=22 December 2015 |url-status=dead }}</ref>}}

===Games===
In 1952, [[Sandy Douglas]] developed ''[[OXO (video game)|OXO]]'', a version of [[noughts and crosses]] (tic-tac-toe) for the EDSAC, with graphical output to a VCR97 6" [[cathode-ray tube]]. This may well have been the world's [[first video game]].<ref name="Cohen">{{cite web |url=http://classicgames.about.com/od/computergames/p/OXOProfile.htm |title=OXO aka Noughts and Crosses – The First Video Game |last=Cohen |first=D. S. |work=[[About.com]] |publisher=[[IAC (company)|IAC]] |date=2014-09-20 |access-date=2015-12-18 |archive-url=https://web.archive.org/web/20151222084801/http://classicgames.about.com/od/computergames/p/OXOProfile.htm |archive-date=2015-12-22 |url-status=live}}</ref><ref name=Wolf3>{{cite book |title=Encyclopedia of Video Games: The Culture, Technology, and Art of Gaming |last=Wolf |first=Mark J. P. |date=2012-08-16 |publisher=[[Greenwood Publishing Group]] |isbn=978-0-313-37936-9 |pages=3–7}}</ref>

Another video game was created by [[Stanley Gill]] and involved a dot (termed a sheep) approaching a line in which one of two gates could be opened.<ref name=smithIEEE /> The Stanley Gill game was controlled via the lightbeam of the EDSAC's paper-tape reader.<ref name=smithIEEE /> Interrupting it (such as by the player placing their hand in it) would open the upper gate.<ref name=smithIEEE /> Leaving the beam unbroken would result in the lower gate opening.<ref name=smithIEEE>{{cite journal |last1=Smith |first1=Alvy Ray |date=9 June 2015 |title=The Dawn of Digital Light |journal=IEEE Annals of the History of Computing |volume=38 |issue=4 |pages=74–91 |doi=10.1109/MAHC.2015.51 |s2cid=10257358 }}</ref>

==Further developments==
EDSAC's successor, [[EDSAC 2]], was commissioned in 1958.

In 1961, an EDSAC 2 version of [[Autocode]], an [[ALGOL]]-like high-level programming language for scientists and engineers, was developed by [[David Hartley (computer scientist)|David Hartley]].

In the mid-1960s, a successor to the EDSAC 2 was planned, but the move was instead made to the [[Titan (1963 computer)|Titan]], a prototype Atlas&nbsp;2 developed from the [[Atlas Computer]] of the [[Victoria University of Manchester|University of Manchester]], [[Ferranti]], and [[Plessey]].

==EDSAC Replica Project==
[[File:EDSAC replica.JPG|thumb|right|EDSAC replica in October 2018]]
On 13 January 2011, the [[Computer Conservation Society]] announced that it planned to build a working replica of EDSAC, at the [[National Museum of Computing]] (TNMoC) on the [[Bletchley Park]] campus. The project is led by [[Andrew Herbert]], who studied under Maurice Wilkes.<ref>{{cite news |url=https://www.bbc.co.uk/news/technology-12181153 |title=Pioneering Edsac computer to be built at Bletchley Park |work=BBC News |date=13 January 2011 |first= Mark |last=Ward |access-date=2011-01-13}}</ref> The first parts of the replica were switched on in November 2014.<ref>[https://www.bbc.co.uk/news/technology-30131447 Museum switches on historic computer].</ref><ref>{{cite book |last1=Hartley |first1=David |last2=Herbert |first2=Andrew |title=Making the History of Computing Relevant |chapter=EDSAC Replica Project |volume=416 |date=2013 |doi=10.1007/978-3-642-41650-7_27 |at=''9 Current Status'', pp. 307–308 |language=en |series=IFIP Advances in Information and Communication Technology |isbn=978-3-642-41649-1 }}</ref> The EDSAC logical circuits were meticulously reconstructed through the development of a simulator and the reexamination of some rediscovered original schematics. This documentation has been released under a Creative Commons license.<ref>{{Cite web |title=EDSAC Logic Rebuild Sub-project |url=http://www.billp.org/ccs/Edsac/index.php |access-date=2023-08-24 |website=www.billp.org}}</ref> The ongoing project is open to visitors of the museum. In 2016, two original EDSAC operators, [[Margaret Marrs]] and [[Joyce Wheeler]], visited the museum to assist the project.<ref>{{Cite web |url=https://www.zdnet.com/article/inside-the-project-to-rebuild-the-edsac-one-of-the-worlds-first-general-purpose-computers/ |title=Inside the project to rebuild the EDSAC, one of the world's first general purpose computers |website=[[ZDNet]] |access-date=24 May 2020}}</ref> As of November 2016, commissioning of the fully completed and operational state of the replica was estimated to be the autumn of 2017.<ref>{{cite web |url=https://www.zdnet.com/article/inside-the-project-to-rebuild-the-edsac-one-of-the-worlds-first-general-purpose-computers/ |title=Inside the project to rebuild the EDSAC, one of the world's first general purpose computers |date=24 November 2016 |first=Danny |last=Palmer |website=[[ZDNet]] |access-date=2016-12-01}}</ref> However, unforeseen project delays have resulted in an unknown date for a completed and fully operational machine.

==See also==
* [[EDVAC]] on which much of the design of EDSAC was based
* [[History of computing hardware]]
* [[List of vacuum-tube computers]]

==References==
{{Reflist|30em}}

==Further reading==
* ''The Preparation of Programs for an Electronic Digital Computer'' by Professor Sir [[Maurice Wilkes]], [[David Wheeler (computer scientist)|David Wheeler]] and [[Stanley Gill]], [[Addison–Wesley]], Edition 1, 1951 [https://archive.org/details/programsforelect00wilk/mode/2up archive.org].
* [http://www.cl.cam.ac.uk/UoCCL/misc/EDSAC99/ 50th Anniversary of EDSAC]&nbsp;– Dedicated website at the [[University of Cambridge Computer Laboratory]].
* {{cite journal |last1=Birch |first1=Bryan |author-link=Bryan John Birch |last2=Swinnerton-Dyer |first2=Peter |author-link2=Peter Swinnerton-Dyer |year=1965 |title=Notes on Elliptic Curves (II) |journal=[[Journal für die reine und angewandte Mathematik|J. Reine Angew. Math.]] |volume=165 |issue=218 |pages=79–108 |doi=10.1515/crll.1965.218.79 |s2cid=122531425 }}
* {{Cite journal |last1=Wilkes |first1=M. V. |last2=Renwick |first2=W. |date=1950 |title=The EDSAC (Electronic delay storage automatic calculator) |journal=Mathematics of Computation |language=en-US |volume=4 |issue=30 |pages=61–65 |doi=10.1090/S0025-5718-1950-0037589-7 |issn=0025-5718 |doi-access=free}}
* {{Citation | editor-last = Copeland | editor-first = B. J. | editor-link = Jack Copeland | title = Alan Turing's Automatic Computing Engine | location = Oxford | publisher = Oxford University Press | publication-date = 2005 | isbn = 0-19-856593-3 | year = 2005 | url-access = registration | url = https://archive.org/details/alanturingsautom0000unse }}
* {{Citation | last = Turing | first =Alan M. | author-link = Alan Turing | title = Report by Dr.&nbsp;A.&nbsp;M. Turing on proposals for the development of an Automatic Computing Engine (ACE): Submitted to the Executive Committee of the NPL in February 1946 | year = 1945 }} reprinted in {{Harvnb|Copeland|2005|pp=369–454}}
* [http://www.billp.org/ccs/Edsac/index.php The EDSAC Rebuild Project – Documentation], and the [http://www.billp.org/ccs/Edsac/Logic/Logic.php?module=Clock reconstructed EDSAC schematics]

==External links==
{{commons category|EDSAC}}
* [https://web.archive.org/web/20101124230055/http://www.dcs.warwick.ac.uk/%7Eedsac/ An EDSAC simulator]&nbsp;– Developed by [[Martin Campbell-Kelly]], Department of Computer Science, [[University of Warwick]], England.
* [http://purl.umn.edu/107711 Oral history interview with David Wheeler, 14 May 1987]. [[Charles Babbage Institute]], University of Minnesota. Wheeler was a research student at the University Mathematical Laboratory at Cambridge in 1948–1951 and a pioneer programmer on the EDSAC project. Wheeler discusses projects that were run on EDSAC, user-oriented programming methods, and the influence of EDSAC on the [[ILLIAC]], the [[ORDVAC]], and the [[IBM 701]]. Wheeler also notes visits by [[Douglas Hartree]], [[Nelson Blackman]] (of ONR), [[Peter Naur]], [[Adriaan van Wijngaarden|Aad van Wijngarden]], [[Arthur van der Poel]], [[Friedrich L. Bauer|Friedrich Bauer]], and [[Louis Couffignal]].
* [http://www.cs.man.ac.uk/CCS/res/res22.htm#b Nicholas Enticknap and Maurice Wilkes, Cambridge's Golden Jubilee]&nbsp;– in: RESURRECTION The Bulletin of the Computer Conservation Society. {{ISSN|0958-7403}}. Number&nbsp;22, Summer 1999.
* [http://www.vintage-icl-computers.com/EDSAC The EDSAC Paperwork Collection at The ICL Computer Museum].
* [https://history.dcs.ed.ac.uk/archive/staging-area/EDINBURGH_REUNION/edsac/edsac.pdf Introduction to programming for EDSAC 2, 1957].
* [https://youtube.com/watch?v=54-9SoeG1is How the EDSAC computer changed science in the 1940s and 50s], a YouTube link on the channel called New Scientist, 7 Mar 2025 (viewed 15 Mar 2025).

[[Category:1940s computers]]
[[Category:1949 establishments in England]]
[[Category:1949 in computing]]
[[Category:Computer-related introductions in 1949]]
[[Category:Early British computers]]
[[Category:One-of-a-kind computers]]
[[Category:Vacuum tube computers]]
[[Category:University of Cambridge Computer Laboratory]]
[[Category:History of the University of Cambridge]]
[[Category:Serial computers]]