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Lookup NU author(s): Professor Brian RandellORCiD


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In October 1975, after an official silence lasting thirty-two years, the British Government made a set of captioned photographs of COLOSSUS available at the Public Record Office, These confirm that a series of programmable electronic digital computers was built in Britain during World War II, the first being operational in 1943. It is stated that COLOSSUS incorporated 1500 valves, and operated in parallel arithmetic mode at 5000 pulses/sec. A number of its features are disclosed, including the fact that it had 5000 character/sec punched paper tape inputs, electronic circuits for counting, binary arithmetic and Boolean logic operations, "electronic storage registers changeable by an automatically controlled. sequence of operations", "conditional (branching) logic", "logic functions pre-set by patch-panels or switches, or conditionally selected by telephone relays", and typewriter output. Professor M. H. A. Newman is named as being responsible for formulating the requirement for COLOSSUS, and Mr. T. H. Flowers as leading the team which developed the machine. An indication is given that the design of COLOSSUS was influenced by the prewar work on computability by Alan Turing, who was employed in the same department of the British Government as Newman. The partial relaxation of the official secrecy surrounding COLOSSUS has made it possible to obtain interviews with a number of people involved in the project. This paper is in the main based on these interviews, and is supplemented by material already in the public domain. It attempts to document as fully as is now permissible the story of the development of COLOSSUS. Particular attention is paid to interactions between the COLOSSUS project and other work carried out elsewhere on digital techniques and computers, and to the role that those involved with COLOSSUS played in postwar computer developments in Britain. Details are given of the careers of the people involved, of how the basic concept of COLOSSUS was arrived at, and of how the first machine was designed and built, and of the subsequent design and and construction of a Mark II version. The paper also attempts to assess Turing's role in the COLOSSUS story, and to relate the work to contemporary work in the U.S., particularly that on ENIAC. The official photographs and the accompanying explanation captions are reproduced in the paper.

Publication metadata

Author(s): Randell B

Editor(s): Metropolis, N., Howlett, J., Rota, G.-C.

Publication type: Book Chapter

Publication status: Published

Book Title: A History of Computing in the Twentieth Century

Year: 1980

Pages: 47-92

Publisher: Academic Press

Place Published: New York, USA

Library holdings: Search Newcastle University Library for this item

ISBN: 9780124916500