Colossus computer in the context of "General Post Office"

Bi-quinary coded decimal is a numeral encoding scheme used in many abacuses and in some early computers, notably the Colossus. The term bi-quinary indicates that the code comprises both a two-state (bi) and a five-state (quinary) component. The encoding resembles that used by many abacuses, with four beads indicating the five values either from 0 through 4 or from 5 through 9 and another bead indicating which of those ranges (which can alternatively be thought of as +5).

Several human languages, most notably Fula and Wolof also use biquinary systems. For example, the Fula word for 6, jowi e go'o, literally means five [plus] one. Roman numerals use a symbolic, rather than positional, bi-quinary base, even though Latin is completely decimal.

Bletchley Park is an English country house and estate in Bletchley, Milton Keynes (Buckinghamshire), that became the principal centre of Allied code-breaking during the Second World War. During World War II, the estate housed the Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis powers – most importantly the German Enigma and Lorenz ciphers. The GC&CS team of codebreakers included John Tiltman, Dilwyn Knox, Alan Turing, Harry Golombek, Gordon Welchman, Hugh Alexander, Donald Michie, Bill Tutte and Stuart Milner-Barry.

The team at Bletchley Park, 75% women, devised automatic machinery to help with decryption, culminating in the development of Colossus, the world's first programmable digital electronic computer. Codebreaking operations at Bletchley Park ended in 1946 and all information about the wartime operations was classified until the mid-1970s. After the war it had various uses and now houses the Bletchley Park museum.
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