Editing Pilot ACE (section)

==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>