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Stepping switch from an original Colossus presented by the Director of GCHQ to the Director of the NSA to mark the 40th anniversary of the UKUSA Agreement in 1986. National Cryptologic Museum, Fort Meade, Maryland, USA. Colossus was a set of computers developed by British codebreakers in the years 1943-1945 to help in the cryptanalysis of the Lorenz cipher used by the German Army. Colossus used thermionic valves (vacuum tubes) to perform Boolean and counting operations. Colossus is thus regarded as the world's first programmable, electronic, digital computer, although it was programmed by switches and plugs and not by a stored program. Colossus was designed by research telephone engineer Tommy Flowers. Alan Turing's use of probability in cryptanalysis contributed to its design.
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