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Colossus reduced the time to work out the Lorenz chi-wheel settings and enabled more messages to be deciphered and the whole code-breaking operation to be accelerated. The information gleaned from the decrypted messages is widely acknowledged to have shortened the war by many months, saving tens of thousands of lives.

The cipher text was input via paper tape and the 2500 valves of Colossus would find the Lorenz machine chi-wheel settings.

By the end of the war, 63 million characters of high-grade German communications had been decrypted by 550 people helped by the ten Colossus computers.

Not until 1975 when the first information about Colossus was declassified could the story begin to be told.

In 1992, Tony Sale and his team began the ambitious task of rebuilding a working Colossus. They succeeded and in 2007 it was tested in the global Colossus Cipher Challenge. Once again Colossus was able to crack the Lorenz code (in 3.5 hours), but was beaten in the race by Joachim Schueth, a professional computer software engineer, who wrote special software for his PC to break the ciphertext in just 46 seconds!

In 2012, a major fundraising campaign, led by TNMOC trustee Tim Reynolds, was launched to convert the old Colossus workshop room into a brand new Gallery. Much work has still to be done to complete perhaps the world's most exciting computing exhibit, but already Colossus is viewable by the public as never before and is set to inspire future generations of engineers and computer scientists.

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The Colossus Computer

Tommy Flowers spent eleven months designing and building Colossus at the Post Office Research Station, Dollis Hill, in North West London. After a functional test, Colossus Mk 1 was delivered to Bletchley Park in late December 1943 / January 1944, was assembled there by Harry Fensom and Don Horwood, and was working in early February 1944.

Colossus was the first of the electronic digital machines with programmability, albeit limited in modern terms. The notion of a computer as a general purpose machine - that is, as more than a calculator devoted to solving difficult but specific problems - would not become prominent for several years.

Colossus was preceded by several computers, many of them being a first in some category. Colossus, however, was the first that was digital, programmable, and electronic. The first fully programmable digital electronic computer capable of running a stored program was still some way off - the 1948 Manchester Small Scale Experimental Machine.

The use to which the Colossi were put was of the highest secrecy, and Colossus itself was highly secret, and remained so for many years after the War. Colossus was not included in the history of computing hardware for decades, and Flowers and his associates were deprived of the recognition they were due for many years.

It has taken nearly fifteen years to rebuild the Mark II Colossus computer in the same position as Colossus 9 originally occupied in Block H. Using only scraps of diagrams, old pictures and half-forgotten memories Tony Sale and his team re-created this fantastic world-first for Britain and set the benchmark for computer conservation.