Colossus | Research & Encyclopedia Articles

Colossus

Colossus was the name of a series of electronic, special-purpose computers, built by the British during World War II to break German military codes. The first Colossus was put into operation in 1943, and was thought to be the first electronic, programmable machine. Later it was learned that Konrad Zuse had built and operated such a machine, his Z3, several years earlier. In all, ten Colossus machines were built. Message-code wheels were among the earliest decoding devices, including one invented by Thomas Jefferson in the late eighteenth century. The first machines that both decoded and printed their results were developed in France in the 1870s. In the 1920s, German code experts developed the first of a series of machines called Enigma that worked like teleprinters, sending messages over telephone lines. But when plain text was typed on the keyboard, it was translated into code before being transmitted. When a coded message was received, the machine automatically decoded it. The first Enigma machines used straight substitutions, such as E for H, F for I, and so on. Polish scientists had invented electromechanical machines called Bombas to decipher German messages that they intercepted between 1928 and 1938. When World War II started in 1939, British scientists could decode advanced Enigma messages. But by 1942, the Germans had built an even more advanced machine that the British called the Fish. It had a set of twelve interlocking code wheels, each with a different diameter. Each wheel also had movable cams that allowed a somewhat random variation in the code-to-key relationship. This made the code difficult and often impossible to break. The British government had established a top-secret decoding operation called Bletchley Park. There, in 1943, a team of British scientists led by Thomas W. Flowers designed a machine to handle Fish's messages. Flowers was a London University-trained electrical engineer. His specialty was the electronics of telephone exchanges, such as the development of electronic switches that were designed to replace the electromechanical switches then used for direct-distance dialing.

_{Heath Robinson.}The first decoding machine used vacuum tube processors for binary numbers. It was faster than previous British machines, able to read 2,000 characters per second and completely automatic. The design was influenced by the British mathematician and computer theorist Alan Turing, whose scientific papers on machine processes were cornerstones of modern computer design and also artificial intelligence. The scientists named it Heath Robinson, after a British cartoonist who drew outrageous machines. The coded German messages were intercepted and each code character, represented by a five-digit binary number, was punched into paper tape. The ends of the message tape were pasted together, forming a loop. A key tape was also punched and made into a loop, but with a different circumference. When the two tape loops were run at the same time for thousands of passes, every possible code-key combination occurred. As the tapes revolved, the patterns of punched holes were "read" by photoelectric cells and translated into electrical impulses. Patterns detected by the machine were sent to code specialists, who provided the final decoded message. But the Heath Robinson design was quickly outdated, as the volume of German messages increased. The scientists began building a new decoding machine, named Colossus. _Colossus Colossus differed from Heath Robinson in several ways. It was entirely electronic. It was digital and programmable, with hand-set switches. The Colossus Mark I was a 1,500 vacuum-tube machine that could handle 5,000 characters per second. The Mark II model, built in 1944, had 2,400 vacuum tubes. It could read 25,000 characters per second because it used parallel processing of five operations at once. An electronic signal generator replaced the key tape. And it had a memory consisting of thyratrons--a type of gas-filled anode-cathode tube that produces a current and holds it until the power is cut off. In all, ten versions of Colossus were built, and some of the scientists involved became the leaders of British computer research in the late 1940s. Flowers later received an honorary degree from the University of Newcastle upon Tyne for his work on Colossus.