Editing Pilot ACE

{{Short description|One of the first computers built in the United Kingdom}}
{{Infobox information appliance
| name         = Pilot ACE
| image        = Pilot ACE.jpg
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| alt          = 
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| aka          = 
| developer    = [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] (NPL)
| manufacturer = 
| type         = 
| releasedate  = {{Start date and age|1950}}
| price        = 
| connectivity = 
| lifespan     = 
| unitssold    = 
| media        = 
| os           = <!-- operating system -->
| input        = 
| camera       = 
| power        = 
| cpu          = approximately 800 [[vacuum tube]]s
| CPUspeed     = 1 [[megahertz]]
| storage      = 
| memory       = 128 32-bit words; later expanded to 352 words
| RAMtype      = [[mercury (element)|Mercury]] [[delay-line memory|delay lines]]
| display      = 
| audio        = 
| service      = <!-- online service/s offered -->
| dimensions   = 
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| touchpad     = 
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}}
[[File:Pilot ACE console.jpg|thumb|Pilot ACE console]]
[[File:Punch cards in tray for Pilot ACE computer built at the National Physical Laboratory c. 1950 (9672239226).jpg|thumb|Punch cards, detail view against dark grey background, for Pilot ACE computer, built at the [[National Physical Laboratory (United Kingdom)]], circa 1950. [[Science Museum London]]<ref name="sciencephoto/ACE">{{cite web |title=automatic computing engine |url=https://www.sciencephoto.com/keyword/automatic-computing-engine |website=Science Photo Library |access-date=14 May 2023}}</ref><ref>{{cite web |title=1950 ace paper cards |url=https://www.scienceandsociety.co.uk/results.asp?search=1&pixperpage=50&searchtxtkeys=1950+and+ace+and+cards+and+paper&lstorients=All+Orientations |website=[[Science & Society Picture Library]]}}</ref>]]

The '''Pilot ACE''' (Automatic Computing Engine) was one of the first [[computer]]s built in the [[United Kingdom]].<ref name="yastes">{{Cite book | first=David M. | last=Yates | title=Turing's Legacy: A history of computing at the National Physical Laboratory 1945–1995 | publisher=[[Science Museum, London]] | location=UK | date=1997 | isbn=0-901805-94-7 | pages=126–146 | url=https://books.google.com/books?id=ToMfAQAAIAAJ }}</ref> Built at the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] (NPL) in the early 1950s, it was also one of the earliest general-purpose, [[stored-program computer]]s – joining other UK designs like the [[Manchester Mark 1]] and [[EDSAC]] of the same era. It was a preliminary version of the full [[Automatic Computing Engine|ACE]], which was  designed by [[Alan Turing]], who left NPL before the construction was completed.

==History==
Pilot ACE was built to be a cut-down version of Turing's full ACE design. After Turing left NPL (in part because he was disillusioned by the lack of progress on building the ACE), [[James H. Wilkinson]] took over the project. [[Donald Davies]], [[Harry Huskey]] and [[Mike Woodger]] were involved with the design.<ref name="yates97">{{cite book| first=David M. | last=Yates | title=Turing's Legacy: A history of computing at the National Physical Laboratory 1945–1995 | publisher=[[Science Museum, London]] | location=UK | date=1997 | isbn=0-901805-94-7 | pages=296, 300, 316 | url=https://books.google.com/books?id=ToMfAQAAIAAJ }}</ref><ref name="woodger51">{{cite journal| last=Woodger | first=M. | author-link=Mike Woodger | title=Automatic Computing Engine of the National Physical Laboratory | journal=[[Nature (journal)|Nature]] | volume=167 | date=1951 | issue=4242 | page=270 | doi=10.1038/167270a0 | bibcode=1951Natur.167..270W | s2cid=4286414 | doi-access=free }}</ref> The Pilot ACE ran its first program on 10 May 1950,<ref name="mck81">{{cite journal| last=Campbell-Kelly | first=Martin | author-link=Martin Campbell-Kelly | title=Programming the Pilot ACE: Early Programming Activity at the National Physical Laboratory | publisher=[[IEEE]] | journal=[[IEEE Annals of the History of Computing]] | volume=3 | number=1 | date=1981 | pages=133–162 | doi=10.1109/MAHC.1981.10015 | s2cid=9711655 }}</ref><ref>{{cite book |last1=Atkinson |first1=Paul |title=Computer |date=2010 |publisher=Reaktion Books |isbn=9781861897374 |page=[https://archive.org/details/computer0000atki/page/39 39] |url=https://archive.org/details/computer0000atki |url-access=registration |quote=Pilot ACE 1950. |language=en}}</ref> and was demonstrated to the press in November 1950.<ref>{{Cite journal |date=1951 |title=Automatic Computing Machinery: News – National Physical Laboratory |journal=Mathematics of Computation |language=en-US |volume=5 |issue=35 |pages=174–175 |doi=10.1090/S0025-5718-51-99425-2 |issn=0025-5718 |doi-access=free}}</ref><ref>{{Cite journal |date=December 1950 |title=9. The ACE Pilot Model, Teddington, England |url=http://www.dtic.mil/docs/citations/AD0694599 |journal=Digital Computer Newsletter |language=en |volume=2 |issue=4 |pages=4}}{{dead link|date=June 2022|bot=medic}}{{cbignore|bot=medic}}</ref>

Although originally intended as a prototype, it became clear that the machine was a potentially useful resource, especially given the lack of other computing devices at the time. After some upgrades to make operational use practical, it went into service in late 1951 and saw considerable operational service over the next several years. One reason Pilot ACE was useful is that it was able to perform [[floating-point arithmetic]] necessary for scientific calculations. Wilkinson tells the story of how this came to be.<ref>{{cite book| title=History of Computing in the Twentieth Century | editor1-first=Gian-Carlo | editor1-last=Rota  |display-editors=etal| publisher=[[Academic Press]] | date=1980 }}</ref>

When first built, Pilot ACE did not have hardware for either multiplication or division, in contrast to other computers at that time. (Hardware multiplication was added later.) Pilot ACE started out using [[Fixed-point arithmetic|fixed-point]] multiplication and division implemented as software. It soon became apparent that fixed-point arithmetic was a bad idea because the numbers quickly went out of range. It only took a short time to write new software so that Pilot ACE could do floating-point arithmetic. After that, James Wilkinson became an expert and wrote a book on [[Round-off error|rounding errors]] in floating-point calculations, which eventually sold well.<ref>{{cite book| first=J. H. | last=Wilkinson | author-link=James H. Wilkinson | title=Rounding Errors in Algebraic Processes | publisher=reprinted by Dover | date=1994 }}</ref>

Pilot ACE used approximately 800 [[vacuum tube]]s. Its [[main memory]] consisted of [[mercury (element)|mercury]] [[delay-line memory|delay lines]] with an original capacity of 128&nbsp;words of 32&nbsp;bits each, which was later expanded to 352&nbsp;words. A 4096-word [[drum memory]] was added in 1954. Its basic clock rate, 1 [[megahertz]], was the fastest of the early British computers. The time to execute instructions was highly dependent on where they were in memory (due to the use of delay-line memory). An addition could take anywhere from 64 to 1024&nbsp;[[microsecond]]s.

The machine was so successful that a commercial version of it, named the [[English Electric DEUCE|DEUCE]], was constructed and sold by the [[English Electric]] Company.

Pilot ACE was shut down in May 1955, and was given to the [[Science Museum (London)|Science Museum]], where it remains today.<ref>{{cite web | url=http://collectionsonline.nmsi.ac.uk/detail.php?type=related&kv=62349&t=objects | title=The Pilot ACE computer | publisher=[[Science Museum (London)]] | location=UK | access-date=2016-08-19 | archive-url=https://web.archive.org/web/20160819152811/http://collectionsonline.nmsi.ac.uk/detail.php?type=related&kv=62349&t=objects | archive-date=2016-08-19 | url-status=dead }}</ref>

==Software==

Installing the magnetic drum in 1954 opened the way to develop a control program for running programs dealing with matrices.  Following urging by J. M. Hahn<ref>J. M. Hahn, Letter to M. Woodger, 20 September 1954</ref><ref>J. M. Hahn, "Some Suggestions for Matrix Routines for Electronic Digital Computers", September 1954</ref> of the British Aircraft Corporation,<ref>M. Campbell-Kelly, op. cit., p. 156.</ref> Brian W. Munday developed General Interpretive Programme (GIP), which required only simple codewords to run a collection of programs called "bricks".  Each brick could perform a single task, such as to solve a set of simultaneous equations, to invert a matrix, and to perform matrix multiplication.  Though there was nothing new in this concept, where GIP was unique was in the simplicity of the codewords that did not specify the bounds of the matrices.  Bounds were taken from the matrix on the drum, where the bounds were the second and third element stored.  When a matrix was punched on cards, the bounds were given as the first two elements.  Thus, once a program was written, it could run automatically with different sizes of matrices, without needing to change the program.
GIP was running in 1954,<ref>M. Woodger, "The History and Present Use of Digital Computers at the National Physical Laboratory." Process Control and Automation, November 1958</ref> and was re-written for DEUCE, the successor to Pilot ACE.

Bricks to be used with GIP were written by M. Woodger, who devised a unique scheme for storing array elements, namely, "[[ block floating point |block floating]]". To use regular floating-point would have required two words for each element.  The compromise was to use a single exponent for all the elements of an array.  Thus, only one word was required for each element.  Only the largest element(s) were normalized. Smaller elements were scaled accordingly.  Though there was some loss of precision associated with the smaller elements, it was not great, considering that elements tended to be within a factor of ten of each other.  The exponent was stored with the matrix, along with the dimensions.

==See also==
* [[List of vacuum-tube computers]]

==References==
{{reflist}}

==Bibliography==
* James H. Wilkinson, ''Turing's Work at the National Physical Laboratory and the Construction of Pilot ACE, DEUCE and ACE'' (in Nicholas Metropolis, J. Howlett, Gian-Carlo Rota, (editors), ''A History of Computing in the Twentieth Century'', [[Academic Press]], New York, 1980)
* Martin Campbell-Kelly, ''Programming the Pilot ACE'' (in ''[[IEEE Annals of the History of Computing]]'', Vol. 3 (No. 2), 1981, pp.&nbsp;133–162)
* B. Jack Copeland (editor), ''Alan Turing's Automatic Computing Engine''. [[Oxford University Press]], 2005, {{ISBN|0-19-856593-3}}
* B. Jack Copeland, ''Alan Turing's Electronic Brain: The Struggle to Build the ACE, the World's Fastest Computer'', [[Oxford University Press]], 2012, {{ISBN|978-0-19-960915-4}}
* Michael R. Williams, ''A History of Computing Technology''. IEEE Computer Society Press, 1997. {{ISBN|0-8186-7739-2}}. Chap. 8.3.4.
* [http://news.bbc.co.uk/2/hi/technology/8683369.stm How Alan Turing's Pilot ACE changed computing], [[BBC News]], 15 May 2010

==Further reading==
* Simon H. Lavington, ''Early British Computers: The Story of Vintage Computers and The People Who Built Them'' ([[Manchester University Press]], 1980)
* David M. Yates, ''Turing's Legacy: A History of Computing at the National Physical Laboratory, 1945–1995'' ([[Science Museum, London]], 1997, {{ISBN|0-901805-94-7}})

==External links==
* [http://purl.umn.edu/107241 Oral history interview with Donald W. Davies], [[Charles Babbage Institute]], University of Minnesota. Davies describes computer projects at the U.K. [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]], from the 1947 design work of [[Alan Turing]] to the development of the two [[Automatic Computing Engine|ACE computers]]. Davies discusses a much larger, second ACE, and the decision to contract with [[English Electric]] Company to build the [[English Electric DEUCE|DEUCE]]—possibly the first commercially produced computer in Great Britain.
* [https://collection.sciencemuseumgroup.org.uk/objects/co62378/main-frame-for-automatic-computing-engine-ace-pilot-model-1949-mainframe-computer The Pilot ACE in the Science Museum Group Collection]
* [http://news.bbc.co.uk/2/hi/technology/8683369.stm How Alan Turing's Pilot ACE changed computing]
* [https://www.theguardian.com/science/video/2011/mar/01/pilot-ace-computer-alan-turing The world's first multi-tasking computer]
* [https://pilotace.virtualcolossus.co.uk Virtual Pilot ACE] A 3D browser based simulation of the Pilot ACE computer

[[Category:1950s computers]]
[[Category:Early British computers]]
[[Category:One-of-a-kind computers]]
[[Category:32-bit computers]]
[[Category:Vacuum tube computers]]
[[Category:Computer-related introductions in 1950]]
[[Category:English inventions]]
[[Category:Collection of the Science Museum, London]]
[[Category:Serial computers]]