Machines that count: Colossus

Computer historian John Pratt, curator of the "Machines that Count" exhibition now at Auckland's Museum of Transport and Technology, provides weekly insights into the history of computing. This week: the Colossus

It’s possible to feature the world’s first computer every week and never mention the same machine twice, but for a lot of people, the seminal machine was the Colossus computer.

Designed by British Post Office engineer Tommy Flowers, the Colossus machine took advantage of 1,500 Argon-filled Thyraton tubes to undertake comparative analysis of intercepted German signals. The German traffic was encoded by an adapted telex machine, and used the 5-bit Baudot code adopted by teleprinters, so Colossus was optimised in hardware as a 5-bit machine.

Colossus could undertake Boolean logic operations — if, then, else logic — and could conceivably have been adapted to do a variety of things, but for the duration of WWII it was kept busy decoding German intelligence. Colossus deciphered some of the war’s most terrifying secrets and laid the groundwork for some of the greatest Allied victories. Many analysts believe that the 63 million characters of top-secret German intelligence decrypted by Colossus (some of it in virtual real-time) ultimately shortened the war by at last two years.

Whatever else it did, Colossus convinced those that knew of its existence that a versatile electronic machine was do-able, and as with many other advances in technology that was all that was required to stimulate the next cycle of innovation.

The ultimate problem with Colossus was that so few people knew of its existence. It was one of Britain’s most closely guarded secrets for many years after the war.

None of the cryptanalysts ever decoded an entire message, and the collated intelligence was delivered by hand to Winston Churchill himself.

During the war the allies knew in advance of the strike that all but obliterated Coventry. Had they used that knowledge to advantage, the intelligence game would have been up. Churchill literally sacrificed Coventry so he could enjoy access to the Fuhrer’s most intimate communication with his extended army. Perhaps jealous of his own reputation, Churchill himself ordered all but one of the Colossi broken up at the war’s end (there were 10). Almost all of the staff at Bletchley Park took the secrets of Colossus to their graves.

In America it had been another story. America might have avoided all-out war, but for the failure of its intelligence efforts, and even though America proved reluctant to “read other people’s mail,” NCR had been making the electro-mechanical “bombes” used to provide high-level analysis at Bletchley Park, and they knew that the British had achieved something greater at Bletchley Park. American intelligence reports even provided some detailed insights into Colossus.

An IBM engineering executive who had enlisted was posted to NCR for the duration of the war, where he almost certainly knew that something had been achieved. Ralph Palmer returned to IBM and headed up the team that created the Model 601-604 electronic calculator.

John von Neuman had associated freely with Alan Turing at Bletchley Park, as well as with J Presper Eckert and John Mauchly at the University of Pennsylvania, where ENIAC, EDVAC and UNIVAC were all conceived. Von Neuman also knew Jay Forrester, who helped develop computer memory. The “von Neuman” architecture with which he is credited owes as much to Turing as to original thought. Others, such as Maurice Wilkes, certainly knew in general terms what had been achieved at Bletchley Park.

One way or another, Colossus seeded the modern computer. While none of the technology of Bletchley Park could be applied directly, Colossus created the ferment in which the modern computer was born. Colossus proved machines could leverage the human mind — and do it at the speed of light.

Whether or not Colossus actually meets the modern definition of a computer is beside the point.

Parts of the Colossus computer are on display in MOTAT’s exhibition “Machines that Count.”

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