Colossus: The Secrets of Bletchley Park's Codebreaking Computers; B. Jack Copeland et al; 2006; Oxford Press; 462 pgs

When I went to UBC, the first computer was called ENIAC. It took some 50 years before the lid came off British secrecy regarding their code breaking machine called Colossus.

For you movie buffs, and purely coincidentally, they was a '70s movie called Colossus: The Forbin Project about a computer that takes over the world. Further on the subject of movies, there are quite a few WWII movies that focus on the infamous Enigma Machine. In fact, the Enigma was commercially available prior to the war. The Germans created several variations on the device, including Tunny… the machine that was usually what they were talking about. The problem of breaking codes was much more complex than just breaking one machine. Each branch of the military had its own version. Some were transmitted in Morse Code over the airwaves. Others used teletype land lines, which introduced further issues. The movie The Imitation Game focused on the German naval codes and Enigma.

Allan Turing had his hand in a lot of this, including developing "bombes", the computers that broke naval code. 

In the 1930's, a "computer" was a person. The modern use of the term came much later. The book follows the developments at Bletchley Park through the eyes of many authors. Thus the book is not sequential in time, nor sharply focused. I was interested because this is part of the history of my profession. It is not called "writing code" for nothing.

Colossus was not a general purpose machine. The "programs" were plug board patches and other settings. Thus Colossus was not a stored-program computer like modern day machines. It was a machine built for a specific purpose, but with many of the innovations (such as interrupts) that make modern day computers possible. Remarkably, Colossus was fast even by todays PC standards, largely because it was both single-purpose, and used many parallel processing tricks that are common today.

Much of what the machine did was driven by the incoming cyphers on paper tape. Today's computers use a high speed clock to driven the computer's operations. Colossus cheated and used the sprocket holes in the tape as the metronome. Thus, the faster the tape, the faster the machine. When the tapes broke, it was quite a mess as it would be moving at about 30 miles an hour!

In 1939, doing math using an electronic machine (no moving parts) was a pipe dream at best. People like Babbage had created monstrous calculating tinker toys that, if nothing else, proved how hard mechanical computing was. Like radar, if WWII had not come along, we might be 20 years or more behind where we are today. The counter argument to this is open development. The British pushed back the boundaries of computing and then kept it secret for decades. 

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