Alan Turing and his Contemporaries: Building the world's first computers
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Alan Turing and his Contemporaries: Building the world's first computers
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| ISBN-13: | 9781780171067 |
|---|---|
| Publisher: | BCS, The Chartered Institute for IT |
| Publication date: | 02/11/2012 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 126 |
| File size: | 8 MB |
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CHAPTER 1
THE IDEAS MEN
Simon Lavington
SCIENCE AT WAR
The momentous events of the Second World War saw countless acts of bravery and sacrifice on the part of those caught up in the conflict. Rather less perilously, large numbers of mathematicians, scientists and engineers found themselves drafted to government research establishments where they worked on secret projects that also contributed to the Allied war effort. This book is about the people who took the ideas and challenges of wartime research and applied them to the new and exciting field of electronic digital computer design. It is a complex story, since the modern computer did not spring from the efforts of one single inventor or one single laboratory. In this chapter we give an overall sense of the people involved and the places in Britain and America where, by 1945, ideas for new forms of computing were beginning to emerge.
In Britain the secret wartime establishment that is now the most famous was the Government Code and Cipher School at Bletchley Park in Buckinghamshire. Bletchley Park together with its present-day successor organisation, the Government Communications Headquarters (GCHQ), may be well known now but in the 1940s – and indeed right up to the 1970s – very few people were aware of the code-breaking activity that had gone on there during the war. The mathematician Alan Turing was perhaps the most brilliant of the team of very clever people recruited to work there. In the spirit of the time, let us keep the story of Bletchley Park hidden for the moment. We shall return to it after introducing examples of other scientific work that went on in Britain and America during the war.
In both countries research into radar featured prominently. The challenge was to improve the accuracy and range of detection of targets, for which vacuum tube (formerly called 'thermionic valve') technology and electronic pulse techniques were stretched to the limit. The Telecommunications Research Establishment (TRE) at Malvern, Worcestershire, became a world-class centre for electronics excellence, especially as applied to airborne radar. Research for ship-borne naval radar was carried out at the Admiralty Signals Establishment (ASE) at Haslemere and Witley in Surrey.
In 1945, as hostilities ended, senior people from the various British and American research establishments visited each other's organisations and exchanged ideas. Amongst the subjects often discussed was the task of carrying out the many kinds of calculations and simulations necessary for weapons development and the production of military hardware. During the war scientific calculations had been done on a range of digital and analogue machines, both large and small. The great majority of these calculators were mechanical or electromechanical. In Britain the mathematician and physicist Douglas Hartree had masterminded many of the more important wartime computations required by government research establishments. In America one particular research group had decided to overcome the shortcomings of the slow electromechanical calculators by introducing high-speed electronic techniques. It was thus that in 1945, in Pennsylvania, the age of electronic digital computing was dawning.
THE MOORE SCHOOL: THE CRADLE OF ELECTRONIC COMPUTING
A huge electronic calculator called ENIAC (Electronic Numerical Integrator and Computer) was developed under a US government contract at the Moore School of Electrical Engineering at the University of Pennsylvania. The spur for ENIAC had been the need to speed up the process of preparing ballistic firing tables for artillery. Leading the development team were two academics: the electrical engineer Presper Eckert and the physicist John Mauchley. As the work of building the huge machine progressed a renowned mathematician from Princeton University, John von Neumann, was also drawn into the project. Von Neumann subsequently (in about 1948) used ENIAC for calculations associated with the development of the hydrogen bomb.
Even before ENIAC itself had been completed the team working on it was producing ideas for a successor computer, to be called EDVAC, the Electronic Discrete Variable Automatic Computer. The team's ideas addressed a challenge: how to make ENIAC more general purpose, so that its benefits could be more easily applied to a much wider range of computational tasks. The ideas were written up by John von Neumann in June 1945 in a 101-page document entitled First draft of a report on the EDVAC. By 1946 copies of this report were being distributed widely and were read with interest on both sides of the Atlantic. A project to build EDVAC was launched in 1946, but due to organisational problems the machine did not become operational until 1951.
Most importantly, however, the EDVAC Report of 1945 contained the first widely available account of what we would now recognise as a general-purpose stored-program electronic digital computer. EDVAC has become formally known as a 'stored-program' computer because a single memory was used to store both the program instructions and the numbers on which the program operated. The stored-program concept is the basis of almost all computers today. Machines that conform to the EDVAC pattern are also sometimes called 'von Neumann' computers, to acknowledge the influence of the report's author.
The June 1945 EDVAC document was in fact a paper study, more or less complete in principle but lacking engineering detail. Once hostilities in the Pacific had ceased there was an understandable desire to consolidate the Moore School's wartime ideas and to explain the details to a wider American audience. Accordingly, the US government funded an eight-week course of lectures in July–August 1946 on the 'Theory and Techniques for Design of Electronic Digital Computers'. Twenty-eight scientists and engineers were invited to attend. Amongst these were just three Englishmen: David Rees, Maurice Wilkes and Douglas Hartree. David Rees had worked at Bletchley Park and then, when the war ended, had joined the Mathematics Department at Manchester University. Maurice Wilkes had worked at TRE during the war and had returned to Cambridge University to resume his leading role at the Mathematical Laboratory (later to become the Computer Laboratory). Douglas Hartree, at that time Professor of Physics at Manchester University but soon to move to Cambridge, was invited to give a lecture on 'Solution of problems in applied mathematics'.
The EDVAC Report and the Moore School lectures were the inspiration for several groups worldwide to consider designing their own general-purpose electronic computers. Certainly Maurice Wilkes's pioneering computer design activity at Cambridge University, described in Chapter 3, grew out of the Moore School ideas. The Moore School's activities were also of considerable interest to Rees's Head of Department at Manchester University, Professor Max Newman, who had been at Bletchley Park during the war. What happened at Manchester after 1946 is explained in Chapter 4.
Although the ideas promoted by the Moore School were of equal interest to Alan Turing, they were to produce a different kind of effect upon his thinking.
THE UNIVERSAL TURING MACHINE
Alan Turing was a most remarkable man. A great original, quite unmoved by authority, convention or bureaucracy, he turned his fertile mind to many subjects during his tragically short life. Though classed in the Scientific Hall of Fame as a mathematician and logician, he explored areas as diverse as artificial intelligence (AI) and morphogenesis (the growth and form of living things).
Why was the young Alan Turing, just back from completing a doctorate in America, one of the first mathematicians to be recruited to help with code-cracking at Bletchley Park in 1939? The answer probably lies in a theoretical paper that he had written back in 1935–6, whilst a postgraduate at King's College, Cambridge.
Turing's paper was called 'On Computable Numbers, with an application to the Entscheidungsproblem'. In plain English, it was Turing's attempt to tackle one of the important philosophical and logical problems of the time: Is mathematics decidable? This question had been posed by scholars who were interested in finding out what could, and what could not, be proved by a given mathematical theory. In order to reason about this so-called Entscheidungsproblem, Turing had the idea of using a conceptual automatic calculating device. The 'device' was a step-by-step process – more a thought-experiment, really – that manipulated symbols according to a small list of very basic instructions. The working storage and the input–output medium for the process was imagined to be an infinitely long paper tape that could be moved backwards and forwards past a sensing device.
It is now tempting to see Turing's mechanical process as a simple description of a modern computer. Whilst that is partly true, Turing's Universal Machine was much more than this: it was a logical tool for proving the decidability, or undecidability, of mathematical problems. As such, Turing's Universal Machine continues to be used as a conceptual reference by theoretical computer scientists to this day. Certainly it embodies the idea of a stored program, making it clear that instructions are just a type of data and can be stored and manipulated in the same way. (If all this seems confusing, don't worry! It is not crucial to an understanding of the rest of this book.)
In the light of his theoretical work and his interest in ciphers, Alan Turing was sent to Bletchley Park on 4 September 1939. He was immediately put to work cracking the German Naval Enigma codes. He succeeded. It has been said that as Bletchley Park grew in size and importance Turing's great contribution was to encourage the other code-breakers in the teams to think in terms of probabilities and the quantification of weight of evidence. Because of this and other insights, Turing quickly became the person to whom all the other Bletchley Park mathematicians turned when they encountered a particularly tricky decryption problem.
On the strength of his earlier theoretical work Alan Turing was recruited by the National Physical Laboratory (NPL) at Teddington in October 1945, as described in Chapter 2. Senior staff at NPL had heard about ENIAC and EDVAC and wished to build a general-purpose digital computer of their own. Turing, they felt, was the man for the job. It is very likely that at NPL Turing saw an opportunity to devise a physical embodiment of the theoretical principles first described in his 'On Computable Numbers' paper. Although he was well aware of the developments at the Moore School and knew John von Neumann personally, Turing was not usually inclined to follow anyone else's plans. Within three months he had sketched out the complete design for his own general-purpose stored-program computer – which, however, did adopt the notation and terminology used in the EDVAC Report. For reasons described in Chapter 2, Turing's paper design for what was called ACE, the Automatic Computing Engine, remained a paper design for some years.
PRACTICAL PROBLEMS, 1945–7
To some extent the problems that beset Turing at NPL also dogged other pioneering computer design groups in the immediate post-war years. The main problem was computer storage. Central to the idea of a universal automatic computer was the assumption that a suitable storage system or 'memory' could be built. The EDVAC Report was very clear about this, stating that the implementation of a general-purpose computer depended 'most critically' on the engineers being able to devise a suitable store.
Many ideas for storage were tried by the engineers of the time; few proved reliable and cost-effective. The trials and tribulations of the principal early British computer design groups are recounted in Chapters 2 to 6. These groups were in the end successful, and indeed in a couple of cases they outpaced the contemporary American groups in building working computers. It is tempting to believe that progress was helped by a continuation of the spirit of inventiveness that the designers had experienced during their wartime service in government research establishments.
All of the designers of early computers were entering unknown territory. They were struggling to build practical devices based on a novel abstract principle – a universal computing machine. It is no wonder that different groups came up with machines of different shapes and sizes, having different architectures and instruction sets and often being rather less than user-friendly.
THE RICH TAPESTRY OF PROJECTS, 1948–54
To set the scene for the rest of this book, the diagram opposite gives a picture of the many British computer projects that bridged the gap between wartime know-how and the marketplace. At the top of the diagram we can imagine the people and ideas flowing out of government secret establishments in 1945. At the bottom are the practical production computers that were available commercially in the UK by 1955. In between the arrows show how ideas and technologies fed through universities and research centres into industry and then out into the marketplace. The left-hand box shows that, at the same time, there were a number of classified government projects that remained secret. Surprisingly, Alan Turing's own attempt at practical computer design at NPL, the Pilot ACE, did not bear fruit until 1950.
Of course, Britain was not the only country actively working on high-speed electronic digital computers in the late 1940s. There were at least a dozen pioneering projects in America. Amongst the earliest of these to become operational were machines called SEAC (May 1950), SWAC (August 1950), ERA 1101 (December 1950), UNIVAC (March 1951), WHIRLWIND (March 1951), IAS (summer 1951) and EDVAC (late 1951). In Germany Konrad Zuse designed a series of ingenious electromechanical computers between 1938 and 1945, but these were sequence-controlled and not stored-program machines. In Australia the CSIRAC electronic stored-program computer first worked in November 1949. Its designer, Trevor Pearcey, had graduated in Physics from Imperial College, London University in 1940 and spent the rest of the war working on radar at the Air Defence Experimental Establishment (ADEE). He moved to Australia in late 1945.
In the next chapter we continue the story of Alan Turing's progression from Bletchley Park to NPL and from thence to Manchester. This represents but one strand of post-war British computing activity. Many other people, as we have already seen, began to be involved in the late 1940s at various places and at various times. It is an intriguing tale.
CHAPTER 2ACES AND DEUCES
Simon Lavington
TURING'S FIRST COMPUTER DESIGN
After almost three years of intensive day-to-day code-breaking activity at Bletchley Park, Alan Turing was gradually moved towards longer-term planning. From 7 November 1942 to 23 March 1943 he was part of a British Joint Staff Mission visiting the United States, where, amongst other things, he saw a secure speech cipher system at Bell Labs. This intrigued him, and he believed he could improve on the design. From the autumn of 1943 Turing was spending two days a week working on speech encipherment at Hanslope Park, which was about ten miles north of Bletchley Park and was the home of various secret communications projects. By the autumn of 1944 Turing was working full time at Hanslope Park on the speech project, which was by now known as Delilah. This activity gave Turing some first-hand experience of electronic design – including some primitive experiments with a form of storage called a 'delay line'. The prototype Delilah began to work in the summer of 1945.
Meanwhile, unrelated developments had been taking place at the National Physical Laboratory (NPL) at Teddington. In September 1944 the mathematician John Womersley had become head of a new Mathematics Division at NPL. One of his briefs was to oversee the development of electronic devices for rapid scientific computing. In the spring of 1945 Womersley went on a two-month tour of American computing installations and became the first non-American to be allowed access to ENIAC.
In June 1945 Womersley met Alan Turing, to whom he showed the draft EDVAC Report. Womersley had read 'On Computable Numbers', and he persuaded Turing to take a job as Senior Scientific Officer in the NPL Mathematics Division, starting on 1 October 1945. Turing was charged with designing an electronic universal computing machine. This was undoubtedly a subject on which he had already been pondering. There is also little doubt that the project was seen at the time by NPL as Britain's answer to the EDVAC proposals.
(Continues…)
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