Alan Turing: Exhibition offers rare glimpse of the man behind the enigma

Here's an excerpt from Turing's paper On Computable Numbers, published in 1936, in which Turing describes his universal machine.

The machine's ability to write and read programs and data to and from memory, known as the stored-program concept, would give it the versatility to tackle almost any problem thrown at it. That flexible stored program architecture is at the heart of the modern computer's ability to carry out anything from word processing to photo editing.

The versatility of the universal machine and today's general-purpose computers stems from their ability to tackle new computational problems without the need to reconfigure the hardware. They can solve new sorts of problems by simply calling on different programs and data from memory.

Not only that, but if a program's instructions are stored inside a writable computer memory, then the program can modify its behaviour as it runs, which made it easier for early computers to carry out intelligent behaviour such as conditional branching.

Turing's interest in building a computer was reinforced by his experiences at Bletchley Park, where he witnessed the Colossus electronic computer helping to decipher intercepted Nazi communications by carrying out high-speed statistical analysis.

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Turing drew up designs for the Automatic Computing Engine or ACE, whose capabilities would be a step beyond those of Colossus, in that it would be a stored-program and general-purpose computer.

ACE, which was built and installed at the National Physical Laboratory at Teddington, generated excited headlines in the British press when it ran its first program in 1950, with one paper proclaiming, "ACE may be the fastest brain, month's work in a minute".

ACE had a clock speed of 1MHz, making it exceptionally fast for its day. A room-sized commercial version of the first model called DEUCE was also produced and became the foundation of the emerging British computer industry.

The first personal desk-side computer, the Bendix G-15, was also based on Turing's ACE design. Marketed by the US-based Bendix Corporation from 1954, the G-15 looked like a jumbo-size kitchen refrigerator and was the forerunner of the modern desktop computer.

Photo: Courtesy of the National Physical Laboratory

Here is a patent related to Turing's ACE. The National Physical Laboratory pilot model of ACE, built by Donald Davies, Michael Woodger and others, was a much smaller computer than Turing originally specified.

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Written after Turing's departure from the National Physical Laboratory in 1950, Computing Machinery and Intelligence is considered to be one of Turing's most important papers.

In it, Turing explored ideas relating to artificial intelligence, attempting to define the most reliable way of answering the question, "Can machines think?".

The paper is where Turing posited the now famous Turing test, a method of assessing whether a computer is sentient. In the test, which Turing refers to as an "imitation game", an interrogator asks questions of two players, one human and one a computer, and tries to determine which is which.

Turing said if a machine were to repeatedly pass itself off as human then it would "near enough" answer the question, "Can machines think?".

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Turing contributed to a major breakthrough in the Allies' ability to crack Nazi codes when he designed the electromechanical bombe machine.

The machine was devised to crack Enigma ciphers, which was used by the German army, navy and air force to protect their communications.

Every day the German military would change the settings used to encrypt messages and each day the Bletchley codebreakers were engaged in a race against time to crack the code.

To help with the decryption, Turing designed the bombe in 1939, a rebuilt version of which can be seen above. Each bombe was built to work as if it were several Enigma enciphering machines wired together and could narrow down the settings used to encrypt each message far more quickly than a human. By the end of the war, more than 200 of the machines were being used in the UK to crack codes.

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Here is the back panel of the rebuilt bombe machine at Bletchley. At the launch of the exhibition, Bletchley Park codebreaker Captain Jerry Roberts, now aged 91, who worked on cracking the Tunny cipher used by Hitler's high command, paid tribute to Turing's contribution in helping decipher Nazi messages.

"In the spring of 1941, Britain was losing the war. The German wolf packs were sinking the ships bringing in food and raw materials to Britain left, right and centre - and of course we didn't know where they were out there, waiting, lurking," he said.

"At that juncture, Turing made his fantastic achievement of breaking naval Enigma. At that juncture, there was no other salvation for Britain. Once naval Enigma was broken, the sinkings dropped by 75 per cent."

But despite his achievements at Bletchley, Turing remained a reserved figure, Roberts recalls.

"We never worked together but I used to see him walking the corridors with his gaze averted because he was a very shy man," he said.

"He was an amazing hero, but he didn't project himself in that way - the opposite in fact."

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At the heart of the Turing exhibition at Bletchley is this statue commissioned by the late Sidney E Frank, an American billionaire.

The 1.5-ton, life-size statue of Turing, the work of artist Stephen Kettle, is made from approximately half a million individual pieces of 500-million-year-old Welsh slate.

Speaking at the launch of the exhibition, Turing's nephew Sir John Dermot Turing said if his uncle had not taken his own life at the age of 41, he might have ended up working in fields beyond computing.

"It's clear that he was moving away from computing machinery and moving towards biological sciences.

"What fascinated him was how things in the natural world could be mathematically modelled, and I think it would have been very interesting to see what he would have contributed in the field of biology. Who knows, he may have gone into other areas as well.

"In a sort of 18th century natural philosopher kind of way he didn't regard anything as being off limits, so he could have gone anywhere," he said.

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The exhibition also offers a glimpse of Alan Turing the man through a collection of personal belongings provided by his family.

Alan Turing's nephew, Sir John, said the family hoped the personal belongings would show the human side of the mathematician.

"You hear about his eccentricities, about chaining mugs to the radiators and cycling through the locality with his gas mask on to ward off hay fever. It can paint a picture of somebody who is perhaps too weird to want to get to know," he said.

"What this new exhibition is trying to do is to share some of the more human side of Alan Turing's nature, to balance out the picture," he said.

Above is a school report for Turing aged 18, which unsurprisingly paints a picture of an academically gifted student.

His maths teacher praises his skill in the subject, saying, "if he does not get flustered and lapse back into slip-shod work he should do very well". The only subject where Turing drew much criticism was in English, where his teacher complained, "His reading is too deliberate."

In a prescient statement, Turing's headmaster summed up the student, by saying, "He seems to be going on very well indeed."

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Having reputedly never had a teddy bear as a child, Turing bought himself one as an adult, which he called Porgy.

During his time at Cambridge, Turing supposedly used to place the bear on a chair and practise his lectures in front of it.

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Here is a biography of Alan Turing, written by his mother Sara and published at her own expense in 1959. This copy of the book was later passed to her granddaughter Shuna.

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While studying mathematics at King's College, Cambridge, Turing took up rowing and was selected as the first reserve in the college's number two boat for the May "bumps".

This picture shows the oar from the boat that was rowed by Turing in 1935, after he filled in when an oarsman broke their foot.

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These pewter tankards were owned by Turing and commemorate the King's College Boat Club Trial Eights in 1931 and 1934. Wear around the handles suggest that they were put to good use by Turing during his time at Cambridge.

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