The Colossus Computer

An engineer by the name of Tommy Flowers invented the Colossus Computer. This was used by British code breakers to read encrypted German messages during the World War II. The Colossus Computer was one of the earliest electronic digital computers. A prototype of this computer, namely Colossus Mark was in operation in 1944. It contained only 1,500 electronic valves, where as the early stored program computers used about 4,000- 18,000 electronic valves. The task of the Colossus was to crack teleprinter messages. It compared two data streams, performing counts based on a programmable Boolean function. While one stream was read at high speed from a paper tape, the other was generated internally. If the count for a setting was above a certain amount, it was given as the output using an electric typewriter. The Colossus was the first to contain shift registers and systolic arrays. This enabled it to do five simultaneous tests; each involving up to 100 Boolean calculations, on each of the five channels on the punch card.

The Colossus used vacuum tubes, thyratrons and photo multipliers to read a paper tape optically, and then applied a programmable logical function to every character. Then a count was kept on how often this function returned true. As the values were more liable to failures, when the machine was switched ON and OFF, the Colossus machine was never turned off until the end of the war. The Colossus was not a true general purpose computer, and had limited programability. The use of the Colossus was kept secret during the war and for many years after the war. Hence, even the inventors of the Colossus did not get their due recognition for many years. The last Colossus is believed to have stopped running in 1960.

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https://www.britannica.com/technology/Colossus-computer