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Alan M. Turing (1912 - 1954)

Alan Mathison Turing was born on June 23rd 1912 in Paddington, London. He was educated at Sherborne School, and then went to King's College, Cambridge in 1931 to read Mathematics.

Alan Turing was a brilliant original thinker. Formally a mathematician, in his lifetime he studied and wrote papers over a whole spectrum of subjects, from philosophy and psychology through to physics, chemistry and biology. He was probably at his happiest when he could combine high-level thinking with hands-on experience with machinery or experiments.

In addition to his many other interests, for most of his postgraduate life he probably had a deeper understanding of computers and their potential in the future than anyone else.

For the full story of Turing's life, visit the Turing Web Site, from which much of this description is derived.

The Turing Machine (1934-36)

Turing graduated from Cambridge in Mathematics in 1934, and was a fellow at Kings for two years, during which he wrote his now famous paper published in 1937 "On Computable Numbers with an application to the Entscheidungsproblem", which postulated the Turing Machine. The Entscheidungsproblem was the mathematical problem of Decidability. (He had been made aware of the problem from a lecture course by Max Newman, and it was to Newman he first showed the paper.)

A Turing Machine was a specific mechanical device that could carry out some specific task in a systematic way. Each Turing Machine would work in a similar manner, using mechanisms related to the computer concepts of input, output and a program. The Universal Turing Machine was essentially a similar device, the specific task of which was to read in a description of any Turing machine in a standard format and then execute any task it was designed to undertake. The Universal Turing Machine would therefore carry out any systematic process man could devise.

The Turing Machine was a somewhat obscure device; there was no intention of building one; it was essentially an abstract concept in a paper considering logic and philosophy. However, relative to the high levels of theory in which he was operating, it was a concrete, buildable machine. It had little similarity to the classic 'von Neumann computer' of 1945, and was not well understood. However the paper anticipated many computer-related concepts, like input, output, memory, coded programs, algorithms, compilers/interpreters, and the finite-state machine.

Turing at Princeton (1936-38)

Turing went to the Institute of Advanced Studies at Princeton, the mecca for logicians, in September 1936 for two years and studied for a Ph.D. under Alonzo Church. Here he met von Neumann, who was like Turing also a brilliant mathematician who at that time only had a secondary interest in practical computers. Von Neumann in fact offered Turing a post in 1938, which would have enabled him to stay in the U.S. However Turing decided to return to his fellowship at Cambridge. He was already showing his practical interest in making computing devices, bringing home from the States a small electronic multiplier he had made as part of an enciphering machine, and in Cambridge starting to build an analogue mechanical device to test the Riemann hypothesis. Soon after his return, in August 1938, he was contacted by the Government Code and Cypher School to act as a consultant in their efforts to break the German Enigma codes.

Bletchley Park : Enigma and the Bombe (1939-45)

The day after the war broke out Turing "joined up" full time at the Government Code and Cypher School, which had just moved to Bletchley Park. He was in the first handful of the stream of able mathematicians drafted into their code-breaking operations. In the next three years Turing was the key figure in the continual battle to decode messages encrypted by the increasingly complex Enigma machines, using the 'Bombe' machine. In particular he took charge of the most difficult code-breaking task, the breaking of the German naval codes. The Bombe was an electro-mechanical device, developed by Turing with help from another mathematician W. G. Welchman, inspired by the Polish 'Bomba'. The periods when the Naval code could be broken saw dramatic reductions in the shipping losses from the Atlantic convoys so essential to the conduct of the Allied war effort.

In November 1942 Turing went to the States for four months, to liaise at the highest level on the current U-boat crisis and on a proposed scrambling device they were building to maintain secrecy in conversations between Churchill and Roosevelt. At this time all other Enigma signals but the German Navy's were being routinely decoded, but the Navy had increased their complexity in February 1942, and the ability to decode their signals had then been lost and had not yet been restored. By the time Turing returned to the U.K., the ability to decode had been restored, under his deputy, and his deputy remained in charge. Turing moved on to a general consultancy role, and to work on a Speech Secrecy system. The American system comprised three roomfuls of equipment (one each for the White House, Pentagon and Whitehall), and Turing thought up a much smaller electro-mechanical device, about the size of a typewriter, which would obviously make the facility more widely available!

Turing was therefore not actively involved in the Colossus project (1943-45) directed by Max Newman, to decode the second generation of German coded communications, which were based on Lorenz machines. These used a completely different mechanism and methodology from the Enigma machines, and correspondingly their codes were broken using a completely different mechanism and methodology. Note however that the decoding procedures for both the Enigma and Lorenz involved imaginative, elaborate and sophisticated theories and processes, and the mechanical device used to provide the initial breakthrough for a new code (i.e. the Bombe and the Colossus respectively) was only one part of a complex operation. Turing made major theoretical contributions to the solution of both the Enigma and Lorenz codes; but whereas he made the key contribution to the design of the Bombe, which was a highly specific electro-mechanical device that bore little relation to a computer, ironically he was little involved in the design of Colossus, which was in effect a special purpose electronic digital computer.

NPL and the ACE (1945-48)

Although Turing was not directly involved in the Colossus project, he knew what was going on. He saw the potential of the electronic computer to realise his long-standing dream of a machine that could carry out processes previously assumed achievable only by the human brain. He well understood that to turn it into a Universal Computer it needed the addition of a large electronic store which could store instruction codes as well as numbers. So in the last year or two of the war he learnt all he could about electronics, partly in connection with his Speech Secrecy project, and was rewarded when at the end of the war he was invited by the National Physical Laboratory to design a computer. This he did by early 1946, designing the ACE around the only viable storage device perceived at the time, the Mercury Acoustic Delay Line. However, there were delays in starting to build his design, and Turing, disillusioned, was allowed to return to Cambridge for a "sabbatical" year (1947/48), returning to theoretical work and studying neurology and physiology. During the period that progress was stalled, Turing spent a lot of time on coding prospective routines, thinking about programming in general, and thinking about how the computer could be used to illuminate the mechanisms of the human mind. On being offered a job by Max Newman, now a Professor in the Department of Mathematics at the University of Manchester, he resigned from NPL and came to Manchester in September 1948.

At Manchester; the Mark 1 (1948-51)

Turing joined the Department of Mathematics as a Reader, with the nominal title of "Deputy Director of the Royal Society Computing Machine Laboratory". (The Royal Society Computing Machine Laboratory was the room the Baby occupied; there was no known "Director"!) It is not clear what his official duties were initially with respect to the Baby/Mark 1 project. Before Turing started work in Manchester he asked for the Baby order code and sent up a routine for long division, which was corrected and got working by Tootill. As soon as the Manchester Mark 1 was generally available for use in April 1949, he enthusiastically set about using it, especially to investigate Mersenne Primes, in collaboration with Newman. In the summer of 1949 he was instrumental in acquiring paper tape equipment and assisted Dai Edwards in attaching it to the Mark 1. Meanwhile, he was continuing his theoretical work and in 1950 published another famous paper "Computing Machinery and Intelligence", which anticipated the subject of Artificial Intelligence.

Turing made contributions to the extra orders added in the Ferranti Mark 1, notably the random number generator. It is also likely that he and Newman influenced the comprehensive set of instructions provided on the Manchester Mark 1 in connection with the double length accumulator, since they required multi-length arithmetic for their Mersenne Primes work. (In practice there was little subsequent usage of the Mark 1s for anything longer than double-length arithmetic).

However, the main formal contribution Turing made to the Mark 1 project was that he worked on providing the early software requirements for the Manchester Mark 1, with the full time help of Cicely Popplewell, and wrote the first programming manual for the Ferranti Mark 1. So it was Alan Turing who was mainly responsible for the decision to use the Base-32 Numerical System and he devised with Cicely the Scheme A method of program organisation. He would therefore have been involved in writing the Scheme A Input routines and standard subroutines for general use.

Final Years (1951-54)

By 1951, Newman and Turing (and indeed Freddie Williams) had withdrawn from active involvement in the Mark 1 Project and subsequent computer development, leaving the newly-arrived Tony Brooker to look after the interests of the programmer.

However Turing was still a keen user of the computer as a tool for his research interests, which now turned to "morphogenesis", the theory of growth and form in biology. And he was was always ready informally to help out other programmers of the Mark 1 with their problems.

Turing's life came to a sad and untimely end in June 1954, from cyanide poisoning, with a verdict returned of suicide, though he did legitimately have cyanide in the house in connection with chemical experiments. It is difficult not to believe that this was precipitated by his trial in March 1952 on charges of homosexuality. As ever Turing was decades ahead of his time and was relatively open about his sexuality. But at that time a homosexual relationship was a crime and a scandal. Turing agreed to take hormone therapy for a year instead of going to prison. However it now became clear that he was a major security risk, both with respect to his work at Bletchley Park and his association with US security from his 1942/43 visit (remember the McCarthy era was now in full flow). He may well have thought that this would hound him for the rest of his life.


In 1945 Turing was awarded the O.B.E. for his vital contribution to the war effort.

In 1951 Turing was elected a Fellow of the Royal Society.

Turing Links : Maths Dept. and the Mark 1, Turing Web Site
Useful Links : Home Page, The Mark 1 Story, Picture Gallery, Mark 1 Literature
Context : 50th Anniversary pages (The Mark 1 story, Celebrations, Virtual Museum)
        at : the School of Computer Science, The University of Manchester
Maintainer : Brian Napper; last updated May 1999 (full acknowledgements)

Copyright University of Manchester 1998, 1999