Colossus Computer
For many years the honor of being the world's first electronic computer was granted to the American ENIAC. In recent years, however, both the United Kingdom and US governments have declassified and released documents presenting more information about Colossus. As a result of this historians have been forced to reconsider and many would call Colossus the world's first electronic computer.
As World War II intensified, the British had pressing needs at home. They knew the Nazis were transmitting messages to troops and to U-boat submarines in code, employing a code generating machine called Enigma. The Enigma had actually been in use by Germany and other European nations since the 1920s. The Poles produced a model that successfully broke the Enigma code in 1932. But by 1939, the Nazis had learned to vary the critical key daily instead of monthly and manual decyphering could not keep up.
Design of Colossus began in March 1943 and the first unit was operating at Bletchley Park in January 1944. The project was directed by the mathematician Max Newman, working with Tommy Flowers and later Alan Coombs.
Colossus was predated by several computers, many that were firsts in some category. Colossus was the first merging all of digital, programmable, and electronic. The idea for Colossus formed from a prior project which produced a special function opto-mechanical comparator machine called the Heath Robinson, and its successors the Old Robinson and Super Robinson.
The primary problem with the Robinsons was synchronizing two paper tapes, one punched with the ciphered message, the other representing the patterns created by the wheels of the Lorenz machine, that tended to stretch when being recorded at over 1000 characters per second. Colossus gave up the second tape by generating the wheel patterns electronically, and could process 5,000 characters (40 feet / 12m of tape) per second. Colossus Mark 2 was less complicated to operate in addition to being more advanced, so greatly sped up the decoding process, which was largely still accomplished by hand.
It included the first ever application of shift registers, allowing five simultaneous tests, each requiring up to 100 Boolean calculations, on each of the five channels on the punched tape; i.e. up to 12.5 million calculations per second. It was not simply able to break the wheel patterns (wheel breaking), but could also learn pin patterns (pin breaking). Both models were programmable employing switches and plug panels, in a manner the Robinsons hadn't been.
Colossus utilized state of the (then) art vacuum tubes, thyratrons and photomultipliers to optically scan a cyphertext from a paper tape and gave a programmable logical function to every character, calculating how frequently this function came back "true". While valves were typically believed to be apt to high failure rates it was recognized that failure happened at power off and on so the Colossus machines, once switched on, were never powered-down until the end of the war.
Although Colossus boasted limited programmability and was the first of the electronic digital machines to do this, it wasn't a true general-purpose computer, not being Turing-complete. It was not then recognized that Turing-completeness was meaningful; most of the other pioneering current computing machines were not either. The idea of a computer as a general-purpose machine, and not simply a large calculator dedicated to solving challenging but single-minded problems, didn't become prominent until several years later.
Colossus was instantly successful, and the Colossus / Tunny combination permitted "high grade" German codes to be decrypted in hours. This proved vastly effective during the D-Day landings. The parallel design of Colossus made it unbelievably quick even by today's measures, a modern Pentium PC programmed to do the same decryption task requiring double the time to break the code. Ten Mark 2 Colossus machines were in use at Bletchley Park by the conclusion of the war.
The role to which the Colossi were assigned was of maximum secrecy, and the Colossus itself was extremely confidential. It consequently had only slight influence on the evolution of later computers; being unknown. EDVAC was the early blueprint which had the greatest influence on later computer architecture. Colossus documentation and hardware were classified from the instant of their existence and continued to be after the War. After the war it is told that Winston Churchill specifically dictated the demolition of the Colossus machines into 'pieces no bigger than a man's hand' and that Tommy Flowers personally incinerated blueprints in a furnace at Dollis Hill. Nonetheless two machines remained in use after the war at GCHQ in Cheltenham, until their destruction in the 1960s.
Information about Colossus came out publicly in the late 1970s after the silence enforced by the Official Secrets Act ended in 1976. Therefore, Colossus could not be admitted into the history books of computing hardware for many years. Newman and his associates were also asked to lived without the acknowledgment they deserved. A 500 page technical report on Colossus and Colossus II, entitled "General Report on Tunny" was released by GCHQ to the national Public Record Office in October 2000; a section is available online . A reconstruction project in May 2004, for the construction of a replica of a Colossus Mk II, was completed by a team led by Tony Sale. It presently is on exhibit in the Bletchley Park Museum in Milton Keynes, Buckinghamshire.
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