Natural Computing

, Volume 10, Issue 4, pp 1383–1405 | Cite as

Unwinding performance and power on Colossus, an unconventional computer

  • Benjamin WellsEmail author


In 1944 the computing machine known as Colossus became operational in support of British cryptanalysis and decryption of German High Command wireless traffic. This first electronic digital and very unconventional computer was not a stored-program general purpose computer in today’s terms, despite printed claims to the contrary. At least one of these asserts Colossus was a Turing machine. While an appropriate Turing machine can simulate the operation of Colossus, that is not an argument for generality of computation. Nor does the behavior of Colossus resemble that of a Turing machine, much less a universal Turing machine (UTM). Nonetheless, we shall see that a UTM could have been implemented on a clustering of the ten Colossus machines installed at Bletchley Park, England, by the end of WWII in 1945. Improvements require even fewer machines. Several advances in input, output, speed, processing, and applications—within the hardware capability of the time and respectful of the specification of Colossus—are also offered.


Colossus Universal computation Small UTM Preclassical computers 



I am deeply grateful to the University of San Francisco Faculty Development Fund, for sponsoring participation in UC09 and for providing stipends to the graduate research assistants who developed the Colossus simulator and worked briefly on the UTM project; the UC09 organizers and reviewers, for cheerful and brilliant hospitality and acceptance of Wells (2009); Mike Stannett, for inclusion in Hypernet and the invitation to speak in the Hypercomputation Workshop at UC09; Jack Copeland, for starting me on the path to hypercomputation in 2000 and to Colossus soon after, and encouraging my participation in UC09; Brian Randell, for lengthy and valuable email exchanges; Wen Dong, for excellence as a student and collaborator; Vaughan Pratt, for the gift of the Hewitt machine and other useful discussions on small UTMs; Damien Woods, for enthusiastic conversation at UC09; the referees, for their kind grace; José Félix Costa, for opening the way and making it easy; and the One True Being, for being.


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  1. 1.Departments of Computer Science and MathematicsUniversity of San FranciscoSan FranciscoUSA

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