Colossus

Colossus was a very early digital electronic computing device, specialized for code-breaking (of the German so-called 'Tunny' cipher, of the so-called 'Fish' cipher family of Baudot teleprinter encodings). They were built in the UK during World War II by team created by Tommy Flowers.

They are often described as 'programmable', but this is incorrect - they had no stored program of any form, and they were not general-purpose; a better description is 'configurable'. They took as input enciphered text characters stored on paper tape, and after performing various logical operations on each, could then increment a counter. That count, along with the configuration, provided the information needed by cryptanalysts to decode the message.

They were notable because they showed that large electronic computing devices could be made to operate reliably; because quite a few were produced; and because many of the post-War computer pioneers in the UK learned about the suitability of electronics for digital computing devices from them.

Background and development

Flowers, who had previously worked on electronic telephone exchange switches for the British Post Office (who were responsible for the telephone system in the UK), had come up with the basic idea of Colossus in early 1943, to replace an earlier Tunny code-breaking machine called 'Heath Robinson', which was mostly electronic, and partially digital.

Construction of the first one, which contained about 1,500 vacuum tubes, started in February, 1943; it first ran in December, 1943. Several more, of a slightly improved design, containing about 2,400 tubes, were ordered, and started to come online in June, 1944. Shrouded in secrecy, all were destroyed after the end of the war; an exact replica has now been created.

Further reading

• Thomas H. Flowers, The Design of Colossus, Annals of the History of Computing, Vol. 5, No. 3, July 1983, pp. 239-252
• Allen W. M. Coombs, The Making of Colossus, Vol. 5, No. 3, July 1983, pp. 253-259
• W. W. Chandler, The Installation and Maintenance of Colossus, Ann. Hist. Comp., Vol. 5, No. 3, July 1983, pp. 260-262
• I. J. Good, A Report on T. H. Flowers's Lecture on Colossus, Ann. Hist. Comp., Vol. 4, No. 1, January 1982, pp. 53-55
• B. Jack Copeland (editor) and others, Colossus: The Secrets of Bletchley Park's Code-breaking Computers, Oxford University, Oxford, 2006
• Paul Gannon, Colossus: Bletchley Park's Greatest Secret, Atlantic, London, 2006
• Tony Sale, The Colossus Computer 1943-1996 and how it helped to break the German Lorenz cipher in WWII, M & M Baldwin, Cleobury Mortimer, 1998

External links

• Jack Good, Donald Michie, and Geoffrey Timms,General Report on Tunny - scan of the complete technical report, which covers the cryptosystem and its cryptanalysis in its entirety
  • The Newmanry History - an OCR-based transcription of an important part of the above
  • General Report on Tunny - page-by-page transcription
• Albert W. Small, The Special Fish Report, December 1944 - effectively an operator's manual for the Colossus
• Brian Randell, The Colossus, in Nicholas Metropolis, J. Howlett, and Gian-Carlo Rota, (editors), A History of Computing in the Twentieth Century, Academic, New York, 1980, pp. 47-92
• The Colossus: its purpose and operation
• The Colossus Rebuild Project
• Explore the Colossus Rebuild