Alan Turing: The Enigma (88 page)

The ostensible reason for sticking to this hideously primitive form of coding, which entailed so much work for the user, was that the cathode ray tube storage made it possible – indeed necessary – to check the contents of the store by ‘peeping’, as Alan called it, at a monitor tube. He insisted that what one saw as spots on the tube had to correspond digit by digit to the program that had been written out. To maintain this principle of correspondence it was actually necessary to write out the base-32 numbers
backwards
, with the least significant digit first. This was for technical electronic engineering reasons, the same as those which obliged cathode ray tubes always to scan from left to right. Another awkwardness arose on account of the five-bit combinations which did not correspond to a letter of the alphabet on the Baudot code. (It was the same problem that the Rockex system overcame.) Geoff Tootill had already introduced extra symbols for these, the zero of the base-32 notation being represented by a stroke ‘/’. The result was that pages of programs were covered with strokes – an effect which at Cambridge was said to reflect the Manchester rain lashing at the windows.

By October 1949 the machine was ready, bar some details, for Ferranti to manufacture. The prototype remained in place while this was done, and the idea was to use the time to write an operations manual and basic programs ready to use on the computer (the Mark I, it would be called), when it arrived.

This was Alan’s next job, and he must have spent a great deal of time in checking the operation of every single function on the prototype, arguing over their efficiency with the engineers. By October he had written out an input routine: that is, a means to persuade the machine when first switched on and empty of instructions, to read in new instructions from a tape, to store them in the right place, and to begin executing them.

But this was low-level work; and on this level the
Programmers’ Handbook
⁷
that he wrote, though full of
helpful and practical advice, involved few new ideas. Indeed, it had nothing as sophisticated as the routines he had devised at the NPL for floating-point numbers. Nor did he do anything inspired in connection with the organisation of sub-routines. This, in the Manchester development, was dominated by the existence of two kinds of storage: on the Ferranti-built machine this would amount to eight cathode ray tubes each with their 1280 digits, and the magnetic drum promising no fewer than 655360 digits, arranged in 256 tracks of 2560 digits each.
^*
Programming revolved around the process of ‘bringing down’ data and instructions from the drum to the tubes, and sending them back again, and the hardware more or less obliged each sub-routine to be stored on a new track of the drum, to be transferred
in toto
as required. The Turing scheme coped with this, but he did not bother with a system for subroutines nested to any depth. He referred to this possibility in a rather flippant passage of the Handbook:

The sub-routines of any routine may themselves have sub-routines. This is like the case of the bigger and lesser fleas. I am not sure of the exact meaning the poet attached to the phrase ‘and so ad infinitum’, but am inclined to think that he meant there was no limit that one could assign to the length of a parasitic chain of fleas, rather than that he believed in infinitely long chains. This certainly is the case with sub-routines. One always eventually comes down to a routine without sub-routines.

but he left this for the user to organise. His own ‘Scheme A’ only allowed for one level of sub-routine calling.

The
Handbook
brought out many of the problems of communication that he faced at Manchester. To Williams and the other engineers, a mathematician was someone who knew how to do calculations; in particular they saw binary notation as something new introduced to them by ‘mathematics’. To Alan Turing, however, all their schemes with base-32 arithmetic and the rest were merely simple illustrations of the deeper fact that mathematicians were free to employ symbolism in any way they chose. To him it was obvious that a symbol had no intrinsic connection with the entity that it symbolised, and so a long paragraph at the beginning of the
Handbook
explained how it was that there existed a convention according to which sequences of pulses could be interpreted as numbers. While this was a far more accurate and also more creative idea than the usual statement that the machine ‘stored the numbers’, it was not immediately helpful to the person who had never before known that numbers could be expressed other than in the scale of ten. It was not that Alan despised doing routine, detailed work within a symbolism such as the Manchester machine demanded: but as in
Computable Numbers
arid the ACE report he
tended to veer from the abstract to the detailed in a way that made sense to him, but not to others. The development that could have absorbed both his liberated understanding of symbolism, and his willingness to do the donkey work when necessary, was that of designing programming languages, the development he described as ‘obvious’ in 1947. But this was precisely what he did
not
do; and thus he failed to exploit the advantage that a grasp of abstract mathematics gave him.
^*

In writing the standard routines for square roots and so forth, he had two assistants after October 1949. One was Audrey Bates, a postgraduate student. The other was Cicely Popplewell, whom he had interviewed for the advertised post in summer 1949. She was a Cambridge mathematics graduate with experience of punched cards used in housing statistics. They both shared his office in that Victorian fortress, the university Main Building, pending the construction of the new Computing Laboratory to house the Ferranti machine. It was not a happy arrangement, for he never really acknowledged their right to exist. On Cicely’s first day he said ‘Lunch!’ and marched out of the room without telling Cicely where the Refectory was. He would talk away himself to anyone who visited, but would be very annoyed if either of them did. Sometimes the shell would crack; they persuaded him to play tennis once, and they were amazed the first time they saw him arrive apparently wearing a raincoat and nothing else, which caused some laughs. Once there was some business of him borrowing a ten-shilling note to pin on his shorts when he went home. But usually they were glad when, as often happened, he did not come in. He made no allowance for the amount they had to learn, and did nothing to mitigate what Cicely felt as ‘an acute inferiority complex’ in terms of speed of brain. Cicely also had the job of smoothing things over with the engineers, when interdepartmental tension was running high.

Using the prototype machine was
no smooth operation. It was comparable with the use of the Robinsons. According to Cicely Popplewell,
⁸
it

…required considerable physical stamina. Starting in the machine room you alerted the engineer and then used the hand switches to bring down and enter the input program. A bright band on the monitor tube indicated that the waiting loop had been entered. When this had been achieved, you ran upstairs and put the tape in the tape reader and then returned to the machine room. If the machine was still obeying the input loop you called to the engineer to switch on the writing current, and cleared the accumulator (allowing the control to emerge from the loop). With luck, the tape was read. As soon as the pattern on the monitor showed that input was ended the engineer switched off the write current to the drum. Programs which wrote to the drum during the execution phase were considered very daring. As every vehicle that drove past was a potential source of spurious digits, it usually took many attempts to get a tape in - each attempt needing another trip up to the tape room.

In fact, writing from the tubes on to the magnetic drum was all but impossible on the prototype. Alan wrote
⁹
:

Judged from the point of view of the programmer, the least reliable part of the machine appeared to be the magnetic writing facilities. It is not known whether the writing was more often done wrong than the reading or less. The effects of incorrect writing were however so much more disastrous than any other mistake which could be made by the machine, that automatic writing was practically never done. …Other serious sources of error were the failure of storage tubes and the multiplier. …

In the hot summer of 1950 it was not unknown for computer users to be sweltering in 90°F heat, and banging the racks with a hammer to detect loose valves.

The autumn of 1949 saw what was to be Alan’s only titbit of hardware design for the Ferranti machine.
¹⁰
One of the hardware functions on which he had insisted was that of a random number generator - a feature not included in his ACE design. His own electronic knowledge stopped short of the necessary practical detail, but with Geoff Tootill’s collaboration he was still able to design his own system. It was one that produced truly random digits from noise, as opposed to something like a cipher key generator that would produce apparently random but actually determined digits. (That, if he wanted it, he would surely program for himself.) Perhaps he based his design on the circuit that produced the Rockex key-tapes at Hanslope.

Geoff Tootill was interested in Alan’s ideas, but some of them were particularly impractical in view of the limited time and effort available. There was, for instance, a scheme he devised for computer character recognition, which would involve an elaborate system with a television camera in order to transfer a visual image to the cathode ray tube store, and reduce it to a standard size. Geoff Tootill was probably the most tolerant of
such dreams, but to him as to all on the engineering side, Alan Turing was the brilliant mathematician (or so they heard) but embarrassingly half-baked engineer. The year 1949 meant the end of his groping efforts to be the academic engineer; there were few who appreciated that the remarkable thing for a British pure mathematician was not a deficiency in electronics, but the willingness to dirty his hands at all.

Meanwhile the more theoretical side of computer development had become a more public question. In 1948 Norbert Wiener had published a book called
Cybernetics
, defining this word to mean ‘Control and Communication in the Animal and the Machine’. It meant the description of the world in which information and logic, rather than energy or material constitution, was what mattered. As such it was heavily influenced by the massive wartime technological developments, although the basic ideas, such as feedback, were hardly new. Wiener and von Neumann had led a conference in the winter of 1943–4 on ‘cybernetic’ ideas, but Wiener’s book marked the opening up of the subject outside the narrow domain of technical papers. In fact
Cybernetics
was still very technical, incoherent, and almost unreadable, but the public seized upon it as a magic key which would unlock the secrets of what had happened to the world in the past decade.

Wiener regarded Alan as a cybernetician, and indeed ‘cybernetics’ came close to giving a name to the range of concerns that had long gripped him, which the war had given him an opportunity to develop, and which did not fit into any existing academic category. In spring 1947, on his way to Nancy, Wiener had been able to ‘talk over the fundamental ideas of cybernetics with Mr Turing,’ as he explained in the introduction to his book.

By 1949 an American supremacy was virtually taken for granted in science as in everything else, and it was a sign of the times that on 24 February 1949 the popular magazine
News Review
,
¹¹
presenting a digest of what Wiener had to say, should explain with pride how British scientists had been able to supply ‘valuable data’ to the American professor when he had flown in. It was as a planet round the Wiener sun that Alan appeared, the photograph of his young and slightly nervous profile standing in marked contrast to the ponderous features of Wiener and the massive visage of the biologist J. B. S. Haldane.

In reality Alan was more than a match for Wiener, and although genuinely sharing many common interests, their outlooks were different. Wiener had an empire-building tendency which rendered almost every department of human endeavour into a branch of cybernetics. Another difference lay in Wiener’s total lack of a sense of humour. While Alan always managed to convey his solid ideas with a light English touch of wit, Wiener delivered with awesome solemnity some pretty transient suggestions, to the
general effect that solutions to fundamental problems in psychology lay just around the corner, rather than putting them at least fifty years in the future. Thus in
Cybernetics
it was seriously suggested that McCulloch and Pitts had solved the problem of how the brain performed visual pattern recognition. The cybernetic movement was rather liable to such over-optimistic stabs in the dark. One story going around, which later turned out to be a hoax, but which found its way into serious literature,
¹²
was of an experiment supposed to measure the memory capacity of the brain by hypnotising bricklayers and asking them such questions as ‘What shape was the crack in the fifteenth brick on the fourth row above the damp course in such and such a house?’. Alan’s reaction to these cybernetic tales was one of amusement.

Another point of difference lay in the fact that Wiener was openly concerned about the economic implications of cybernetic technology. The war, for him, had not changed a conviction that machines should be made to work for people rather than
vice versa
. His comment that factory robots would put the people they replaced in the position of competing against slave labour, and his daring description of the principle of competition as a ‘shibboleth’, put him on the extreme left of 1948 American opinion. It was no accident that on his visit to Britain Wiener had consulted the left-wing luminaries of science, J.D. Bernal and H. Levy, as well as Haldane.