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Colossus computer

Colossus was the name for any of at least two versions of the world's first programmable (to a limited extent) digital electronic computer.

It was built by the British Post Office Research Station at Dollis Hill, by Thomas Flowers and crew to a design by Max Newman and associates of Bletchley Park.

Table of contents
1 Purpose
2 Origins
3 Design and operation
4 Influence
5 Reconstruction
6 See also:
7 External link


It was primarily designed for Cryptanalysis in an attempt to break one of the Fish cyphers (a Bletchley Park term) used by the German military for its most secure strategic communications. These were teletype cypher machines in the spirit of that first proposed by Col Parker Hitt of the US Army around WWI. The German machines were, essentially, attempts at an electromechanical implementations of the one-time pad cypher invented by Gilbert Vernam (Bell Labs) and Joseph Mauborgne (Signal Corps, USA) in the US at the end of WWI. The most important was a teletype based machine built by Lorenz Electric, the SZ-40 (and later SZ-42) Schlusselzusatz (meaning, more or less, 'auxiliary key').

Another, different, teletype cypher machine was designed and built by Siemens & Halske, the T-52 Geheimfernschreiber (meaning, more or less, 'secret writer'). Early versions of the Siemens machine (the T-52a and T-52b) were used to send signals between Germany and Norway over a cable running through Sweden. The Swedes tapped the cable, copied the traffic, and Arne Beurling, a Swedish mathematician, broke the cypher. Later production versions of the T-52 (there were variants through 'e') were considerably more secure, and quite hard to break even for Bletchley Park. Some of the T-52 traffic was also sent over Luftwaffe Enigma networks which were much more easily broken, and so T-52 traffic was a lower priority for Bletchley Park than might have otherwise been expected.

The one-time pad requires a random sequence. It is combined with the plaintext (bit by bit, usually as character by character) resulting in the cyphertext which is transmitted. On receipt, the same random sequence is combined with the cyphertext (again usually character by character), and because the combining operation is reversible in a particular way (see XOR, for example) the output is the original plaintext. In the German Fish machines, the 'random' sequence was produced by various electromechnaical arrangements (on one of them, these were rotors somewhat as in the US SIGABA machine), and the sequence wasn't actually random. Because there were patterns, they could be predicted if the cryptanalysts were sufficiently clever, and plaintexts recovered. In the case of the Lorenz machine, Col John Tiltman and Bill Tutte of Bletchley Park were sufficiently clever. In the case of the early Siemens machine, Buerling had been sufficiently clever.


The idea for Colossus developed out of a prior project which produced a special purpose opto-mechanical comparator machine called the Heath Robinson. The Colossus was intended to be more flexible and faster, and in the bargain less subject to the vagaries of paper tape stretching when moving at high speeds; it was decided to make it programmable in a way the Heath Robinson had not been. The project was headed by the mathematician Max Newman. It started early in 1943 and the first version of the machine (Mark 1 Colossus) was finished and installed by about January 1944, to be followed by the improved Mark 2 Colossus in June 1944. Ten Mark 2 Colossus machines were in use at Bletchley Park by the end of the war.

Design and operation

Since solid state electronics had not yet been invented, the machine used vacuum tubes and optical devices to read a cyphertext from a paper tape and then applied a programmable logical function to every character, counting how often this function returned "true".

Whilst Colossus featured (limited) programmability and was the first of the electronic digital machines to do so, it was not a true general purpose computer, not being Turing-complete. It was not then realized that Turing completness was significant, and most of the pioneering modern computing machines (eg, the ABC machine, the Harvard Mark I electro-mechanical relay machine, the Stiebitz Bell Labs relay machines, Konrad Zuse's first two designs, ...) weren't either.


Colossus was a highly secret device, and had therefore not much influence on the development of later computers. EDVAC was the early design which had the most influence on subsequent computer architecture. Colossus documentation and hardware were classified from the moment of creation and remained so after the War. Indeed, nearly all of both was destroyed in the 1960s. It is said that Winston Churchill specifically ordered the destruction of the Colossus machines into 'pieces no bigger than a man's hand' and that Tommy Flowers personally burned blueprints in a furnace at Dollis Hill. Information about Colossus emerged publicly in the late 1970s after the secrecy imposed by the official secret ended in 1976. Thus, Colossus could not be included in the history of computing hardware for many years. Newman and his associates also were deprived of the recognition they were due.


A copy of one of the Colossus versions has been partly completed by Tony Sale and is on display in the Bletchley Park Museum in Milton Keynes, Buckinghamshire.

See also:

External link

Colossus was also the name of a fictional computer that takes over the world in the 1969 science fiction film "Colossus: the Forbin Project," loosely based on the novel Colossus by Dennis Feltham Jones. It has been speculated that Jones named his rogue computer after the "real" Colossus, because of the secrecy that surrounded the project.