A Post-modern Colossus

There is something distinctly surreal about the latest project to pit a reconstructed Colossus against a Pentium PC in a codebreaking challenge. Unlike the Science Museum’s six-year effort to build a Babbage Difference Engine, which was aiming at determining whether or not a working calculating machine could have been made with 18th century technology and accuracy, the Colossus is known to have worked, and very efficiently, too.

One of the candidates for ‘the first digital computer’, the Colossus was a British wartime machine, designed to decode German messages encrypted using the Lorenz teleprinter system. Based on principles from mathematician Max Newman and designed by engineer Tommy Flowers, the Colossus was based on the use of vacuum tubes as switches and was programmed by setting parameters on a switchboard and running an encoded teletype paper tape through a reader. While it was not actually a ‘digital computer’ in the sense of a truly Turing-complete machine with the ability to store and run programs, it did represent a significant step in the development of such machines. While the Colossus was purposely left to obscurity after the end of the war, as a matter of national security, with eight out of the ten machines broken down into small pieces, it has received a degree of attention since its emergence from behind the British Official Secrets Act in 1976. The codebreaking operation at Bletchley Park was the focus of considerable amounts of national pride in Britain after the war, as it is considered to have had a decisive effect on the course of World War II.


The very idea that a proto computer designed and built in the 1940s could even be considered as competition for a state-of-the-art laptop in 2007 has a remarkable innocence about it, considering that while 63 years might have passed in human terms, the continuing adherence of semiconductor circuits to Moore’s Law (that average processing power doubles every two years) means that 2007 laptop is 100,000,000 times faster. It is highly unlikely that this remarkable challenge was seriously thought to have been possible for the Colossus to win, given its dependence on paper tape and glass vacuum tubes, despite the same software algorithms in use throughout the challenge. That said, Tony Sale insists in a BBC interview that a Colossus emulator running on a PC takes ‘about the same time’ to break a cipher as the reconstructed machine.

The most ironic part of this diversion into computer history is that the Colossus machine that is being used for the Cipher Challenge contains a significant element of reconstruction, due to the aforementioned destruction of the original Colossi (the remaining two were destroyed in the 1960s). For an event that promises the spectacle of a first-generation technology pitted against third-generation, the ‘aura’ of authenticity of the original is distinctly tarnished. The Colossus in use last week is made up of a proportion of original parts combined with detail pieced together from fragments of original circuit diagrams, engineers’ memories and a wartime report by American servicemen at Bletchley Park released from the US National Security Agency in 1995. The reconstruction of the machine from such sources, rather than the revamp of a mothballed original, does send the project into the realm of simulation, particularly as it is impossible to tell how accurate the ‘rebuild’ actually is. This is a common issue with reconstruction projects and one that is generally blithely ignored by the reporting press, as they interview enthusiastic ‘rebuilders’ striving for an unachievable Platonic ideal.


If the actual original is unobtainable, as is often the case, the reconstruction is allowed to stand in for the original, as is common practice in museums and heritage centres throughout the world. It is not always as clearly telegraphed as in the Science Museum project, where the work of reconstruction was largely carried out within an exhibition setting. The Difference Engine project was unusual as it was clearly denoted as a contemporary attempt at following Babbage’s technical drawings and diagrams, which had never been fully realized in the first place. While the Science Museum’s reconstruction remained faithful to Victorian machining techniques and tolerances, a number of adjustments to the Engine were carried out as various details were exposed as being insufficiently though-out, no surprise for a machine which only ever existed in paper format and as small test pieces. On the other hand, the reconstructed Colossus does actually contain parts from the original machines, as well as standard parts dating to the same period and represents a different kind of simulation. The lack of original drawings requires a certain amount of ingenuity in the simulation of parts, many of which have been appropriately simulated on Tony Sale’s CAD system.

I would argue that the cultural force that allows the reconstructed nature of this Colossus to recede in importance is that of nostalgia. The uncertainties of the 21st century have created an environment where the past is valorised for its simplicity. This is particularly noticeable in attitudes to World War II, where Barthes’ ‘myth’ of solidarity in the face of a common enemy colours much of the discourse, harking back to the task of ‘winning the war’. An entire minor section of the media industry is dedicated to discussing and dissecting those events and is particularly noticeable in the numbers of documentaries on history-orientated channels on WWII. Of course, this is facilitated by the widespread use of cinema cameras in a war situation for the first time, in addition to the increasing length of time elapsed, as the war passes slowly out of living memory. Its not unlikely that the experience of war on the home front seems much more romantic to the children and grandchildren of survivors, compared to those who lived through it.

However the reconstructed machine may be viewed, the fact remains that the Cipher Challenge attracted a great deal of publicity for the Museum of Computer History, publicity that it has struggled to attract over the years. At present, the Museum is part of the Bletchley Park complex, relying heavily on volunteer labour and donations. The connection with the Heinz Nixdorf Museum in Germany, who transmitted the cyphertext used in the challenge, has widened the audience outside of the English-speaking world and the news coverage on the BBC has focussed attention on the history and heritage of computing. Although the Challenge was won by Joachim Scheuth, a German amateur radio ham and programmer, in a time of 1 1/4 hours, the spectacle of a simulated set of valves clicking and whirring their way through 3 1/2 hours worth of calculation is not something you see every day.

Sorcha O’Brien


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