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Birth of the digital computer

Colossus was an electronic digital computer, built during WWII from over 1700 valves (tubes). It was used to break the codes of the German Lorenz SZ-40 cipher machine that was used by the German High Command. Colossus is sometimes referred to as the world's first fixed program, digital, electronic, computer. In any case, it was conceived before the American ENIAC.
Colossus was designed by Tommy Flowers, an electronics engineer of the Post Office Research Station (part of the General Post Office, GPO) at Dollis Hill (UK), with input from Harry Fensom, Allen Coombs, Sid Broadhurst and Bill Chandler. It was used to solve a problem posed by Max Newman, a codebreaker at Bletchley Park.

The image on the right shows one of just eight photographs of an original Colossus Mark II in action that were taken during WWII. The images were used in 1993 by Tony Sale and his team of volunteers, to start the Colossus Rebuild Project.
One of only eight surviving photographs of Colossus taken during WWII

One of the most prominent parts of Colossus is the input device on the right, nicknamed 'the bedstead'. It is an optical reader for punched paper tapes, than can read data at the phenomenal speed of 5000 characters per second! A complex system of supporting wheels is necessary to regulate the tape tension and prevent the tape from ripping apart at this speed.
Contrary to popular believe, Colossus was not used to break the German Enigma machine. The Enigma was broken by means of an electro-mechanical machine, known as the Bombe, designed by Alan Turing and Gordon Welchman.

Colossus on the other hand, was used to break the Lorenz SZ-40/42. A highly sophisticated teleprinter attachment with no less than twelve complex cipher wheels. It was used by the German High Command for messages at the highest level, for example between Hitler and Field Marshal Rommel in North Africa.

Colossus rebuild
Immediately after WWII, most Colossus computers were ordered to be demolished. They were either destroyed or dismantled and the components were reused. Two machines were kept for future use by GCHQ during the Cold War. In 1959 and 1960, when newer technologies had emerged, these two machines were finally decomissioned and were eventually dismantled.
In 1991, a team led by Tony Sale started playing with the thought that it might be possible to rebuild a fully operational Colossus computer.

In 1993, he set out to start the rebuild project, based on the very limited information that he had gathered. The first parts of Colossus were switched-on on 6 June 1996, in the presence of HRH the Duke of Kent and the original designer Tommy Flowers. The latter passed away in 1998 at the age of 92. In November 2007, the rebuild project was completed and Colossus was staged in an international Cipher Challenge contest.
Tony Sale in front of Colossus. Copyright South Beds News [4].

Since then, work has started to convert Colossus (now called Colossus-I) into Colossus Mark II. As the Mark II version contains over 1000 more valves than the original machine, this project would, no doubt, keep Tony and his team busy for the next couple of years. Sadly, Tony Sale passed away unexpectedly on 28 August 2011 at the age of 80, leaving behind the Colossus legacy. Luckily though, his achievement was well-documented so that his team could complete the work.
Colossus in September 2013 Colossus, with Kevin Coleman explaining it to the public. Teleprinter in front of Colossus Close-up of Colossus Colossus seen from the right Colossus seen from the front right A view trough the bedstead Rear view of Colossus
Colossus rear view Colossus detail Close-up of the valves Dust settled down on the thermionic valves Valve close-up Stepping relays and valves inside Colossus Rack detail Status lamps on top of Colossus

Colossus today
Tony's legacy has been preserved well. In 2012, the Colossus display in H-Block at Bletchley Park has been refurbished completely. The ceiling has been painted black and the floor has received a new carpet. More importantly, there is now much more room for the audience, who can walk all around Colossus now. The image above shows Colossus in September 2013 during a presentation by volunteer Kevin Coleman. At the very left is Chief Colossus Engineer Phil Hayes.

Colossus in September 2013

As it is now possible to walk around Colossus, you can 'view through' the machine and see the many, many wires, stepping relais, and thermionic valves (vacuum tubes) behind the front panel.

Stepping relays and valves inside Colossus

Real life visit
If you are interested in electronics, computer technology, history of WWII, etc., Colossus is a must see. Only when you are physically inside the room where Colossus is located, can you appreciate the efforts of its designers, but also of its re-builders. You can see it in action, feel the heat generated by the valves and sense the typical smell of working electronics. If you are visiting Bletchley Park, you must take some time to visit The National Museum of Computing (TNMOC) in Block H. The volunteers will be more than willing to tell you all you want to know about Colossus.
Colossus in 2004
Below are some photographs of Colossus that we took in November 2004. We apologize for the rather poor quality; at the time we were still using an analog camera.
The bedstead of Collossus Detail of the power supply Close-up of some of the valves Using a modern ascilloscope to check the operation of the optical tape reader Walking through Colossus Looking at a valve rack inside colossus The optical tape reader seen from the rear The programming panel

Enigma and the Bombe
It is sometimes assumed, even by respected writers, that Colossus was used to break the German Enigma codes. This was not the case however. Colossus was used to break the codes of the far more advanced Lorenz SZ-42, used by Hitler's High Command (Oberst Kommando des Heeres).
Enigma instead, was broken with help of an electro-mechanical machine, called the Bombe, designed by Alan Turing and Gordon Welchman at Bletchley Park and built by Harold (Doc) Keen at the British Tabulating Company (BTC).

Over 200 of these machines were installed at Bletchley Park and its outposts, attacking the German Enigma messages on a daily basis.

 More information
Click here to read about the Bombe machine

  1. B. Jack Copeland, Colossus, Breaking the German Tunny Code at Bletchley Park
    An illustrated history. The Rutherford Journal, Volume 3, 2010.

  2. Tony Sale et al., Colossus Rebuild Project
    Date unknown. Retrieved March 2011.

  3. Tony Sale, Colossus 1943-1996,
    And How it Helped to Break the German Lorenz Cipher in WWII.
    ISBN 978-0947712365.

  4. South Beds News, Photograph of Tony Sale in front of Colossus
    Website The Telegraph. 31 August 2011.

Further information

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Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Saturday, 11 January 2014 - 12:51 CET
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