By Mark Ward

Technology Correspondent, BBC News

Please turn on JavaScript. Media requires JavaScript to play. Advertisement This week, BBC News is running a series of articles about pioneering British computers and British computer pioneers. The series begins with a look at research into computers developed at GCHQ after the Second World War. The influence of the 1939-45 war on the development of computers is well known. That conflict spurred the creation of pioneering machines such as Colossus at Bletchley Park and Eniac in the US. Also, many of the engineers who contributed to wartime inventions such as radar went on to develop other influential machines at Cambridge and Manchester, and at companies such as Elliott and Ferranti. Research by computer historian Simon Lavington has shown that efforts to produce special purpose code-cracking machines, such as Colossus, did not stop when hostilities were over. Speed king Professor Lavington said the General Communication Head Quarters (GCHQ) in Cheltenham built up its own team after the war for specific projects. What those machines were used for is still covered by the Official Secrets Act, but Prof Lavington obtained permission to talk to some of the engineers behind them about their technical details. Of most interest, he said, was a machine called Oedipus that was almost unmatched by any other machine when it went into service in 1954. "Oedipus certainly outperformed all other available general purpose computers both in its processing speed and online storage," he said. "For particular tasks it was about 10,000 times faster than the fastest commercially-available computer at that time - an IBM 704," he told BBC News. "In those terms Oedipus was a supercomputer." It was not until the 1990s that general purpose machines could match Oedipus for searching through a database and finding a particular term, said Prof Lavington. The machine had three separate memory stores for the data: a magnetic drum, a large semiconductor associative (ie content-addressable) store and a RAM cache. In total, this amounted to more than 200 kilobytes of on-line memory. This was huge in comparison to other machines at the time, which rarely mustered half as much. "From an engineering point of view it was a most interesting piece of apparatus," he said. In particular, he said, the way its memory was organised was unique for the time. Total recall With general purpose computers in the 1950s, values were typically stored at addressable locations in memory. The instructions those computers could carry out were typically limited to simple arithmetic functions such as addition and comparison, on one pair of values at a time, he said. Oedipus' capabilities went unmatched until the early 1990s By contrast, Oedipus had an associative memory that stored coded words and phrases that could be searched by value, rather than by address. This associative store was used to compare large amounts of characters in parallel, as quickly as possible. Oedipus could hold 160,000 characters of particular phrases on its magnetic drum memory and a further 60,000 characters in its read-only associative store, which consisted of huge numbers of semiconductor diodes. Modern computers can do something similar in serial fashion, said Prof Lavington, when they are asked to search for all instances of a word in a document. Oedipius stayed in use until 1959 and was finally dismantled in 1962. Its name derived from the fact that it had a large dictionary at its heart. Although permission was given to talk to some of the men who worked on Oedipus, and some of the circuit diagrams have been declassified, Prof Lavington said that GCHQ has not yet been able to find any physical remains of the machine at Cheltenham. "After a lapse of about 50 years, GCHQ could not find photographs or any bits of hardware," he said. The secrecy surrounding its design and operation means that Oedipus has had little impact on computer history. Prof Lavington said he will reveal more of its history in a book he is writing about Elliott Computers - one of the firms that aided its development. The book, called Moving targets: Elliott-Automation and the dawn of the computer age in Britain, is due out in late 2010.



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