University of Cambridge Computer Laboratory

EDSAC 1 and after - a compilation of personal reminiscences

As part of the EDSAC 99 celebrations Dr David Hartley collected and edited a informal collection of reminiscences from those involved with the EDSAC and the early days of the Computer Laboratory.

May we encourage anyone else with something to relate to put finger(s) to keyboard, and put down - in whatever form you wish - your remembrances of the early days of the Laboratory to add to this collection. We are interested in anything about the early years of the Laboratory, experience with EDSAC and so on, up to the time of the demise of the Titan computer in the early 1970s. We prefer short rather than long pieces, as these will be easier to incorporate into an anthology.

You are, of course, welcome to submit a piece in any manner, but we have an overwhelming preference for something in a machine-readable format. Submissions in writing will be more difficult to deal with, and we certainly cannot undertake to capture verbal reminiscences given over the phone. Best would be plain text in an e-mail message sent to David.Hartley@ccdc.cam.ac.uk Please remember to mention your position in the laboratory and to give the dates of your association with it.

We shall assume that anything submitted comes with the author's permission to be edited and reproduced.



Foundation of the Mathematical Laboratory


Summer Schools
Diploma students in the 1950s


Diploma students in the 1960s




I was asked by the Laboratory to collect and edit, in an informal way, any reminiscences that those involved with the EDSAC and the early days of the Computer Laboratory cared to submit. We had been approached by many who would like this to be done, and there it seemed likely that a small amount of editorial effort would glean a fascinating amount of historical information that would make interesting reading.

A general encouragement was made to those with something to relate to put finger(s) to keyboard, and put down - in whatever form they wished - their remembrances of the early days of the Laboratory. We stated an interest in anything about the early years of the Laboratory, experience with EDSAC &c., up to the time of the demise of the Titan computer in the early 1970s.

I have ordered the submissions more or less chronologically, grouping together those that have a common theme; some have been split to fit this approach. A list of contributors is given at the end.


Foundation of the Mathematical Laboratory

John Lennard-Jones (son of Sir John Lennard-Jones ScD FRS, founder of the Mathematical Laboratory

My father was a mathematician who had the unusual distinction of holding a chair of theoretical physics in Bristol followed by a chair of theoretical chemistry in Cambridge. His main interest was in atomic and molecular structure, especially the forces between atomic particles, the nature of chemical bonds and such basic matters as why water, unlike most other compounds, expands when it freezes. He gathered around him a research group in Cambridge and his interest in numerical calculations arose from their work.

To this end he arranged for a working version of the newly-developed Bush differential analyser to be built out of Meccano with the help of Mr Bratt and Dr Wilkes. This first machine which occupied a table top, about the size of a table tennis table, was housed in the Department of Chemistry. Later, a larger and more sophisticated machine was built and housed in the new Mathematical Laboratory in the former Anatomy School. As a boy, I can remember assisting with the input of data to both machines by moving a transparent cursor over a curve by rotating two handles on the X and Y axes.

The new Laboratory was open at the beginning of the War in 1939 and my father offered its facilities to the needs of arms development. My memory is of a busy department with the Bush machine in the centre of the building, presumably being used for weapon research. Later in the War I can remember spending whole nights in the laboratory as part of the air raid precautions against incendiary bombs for which we were provided with a "stirrup" pump and pails of water.

As the war developed my father spent more and more time away from home advising on national projects and was soon appointed as Chief Superintendent of Armament Research at Fort Halstead in Kent. Later, he became Chief Scientist at the Ministry of Supply.

When he returned to academic life after the end of hostilities, his basic research had been brought to a halt for many years. He began to pick up the threads and also developed an interest in general principles of education. He accepted appointment as Principal at the recently founded University of Keele in the early 1950s but his contribution there was cut short by his death at the age of 60 in 1954 at a time when his scientific work was again becoming productive.



EDSAC 1 construction

John Bennett (Research Student 1947-50)

Note: This and subsequent sections by John Bennett have been extracted, with the author's permission, from the Autobiographical Snippets chapter of In the Beginning - Recollections of Software Pioneers by Robert L Glass (IEEE Computer Society, 1998 - ISBN 0-8186-7999-9)

EDSAC was built in a room on the top floor of a building that was once the dissecting room of the Cambridge University anatomy school. This historical association brought with it an advantage and a disadvantage. The advantage came in the form of a large goods lift that had been designed to carry two cadavers. The disadvantage became apparent in the summer when the formalin (used to preserve cadavers) that had impregnated the floorboards over the years was vaporised by the heat. The smell of the formalin vapour is very penetrating!

Robin Stokes (User/Research Student 1948-49)

I attended a course by Maurice Wilkes on computing, in which he first taught some useful tricks for efficient use of such machines, and then went on to explain the general principles of the design of EDSAC. We were shown the assembly line with girls soldering military surplus acorn valves into arrays of logic gates, and I was particularly fascinated by the mercury delay line memory idea.

I did not imagine that fifty years later I would be using one of EDSAC's descendants, about a million fold faster and more powerful, to send birthday good wishes from my home on the other side of the world.

Herbert L Norris (Technician 1951-63)

When working at the Engineering Laboratory (1940 - 1951), I produced a cylinder of brass about 3" diameter and 6" long, this was eventually to be covered by a ferrite material and to have a 'Head' travelling along it which was to read magnetic signals from this drum. I did not realise that I was in at the beginning of computers.

I was asked if I would like to join the Maths Lab in January 1951, and I was very pleased to do so. I never saw the drum working and I believe there was a problem with spraying the ferrite material on to give an even coat, and the development of the heads had not progressed enough to be run close to the surface.

I joined Gordon Stevens in the workshops to do mainly maintenance work on the punched paper-tape readers, tape comparators, teleprinters and punched paper-tape printers used on the output from EDSAC. (We fitted mechanical checking equipment to these, which, until replaced by photoelectric cells, was more trouble than it was worth). These mechanical devices were working at about 19 characters per second.

Gordon at this time was working on a memory bank for EDSAC, which was several tubes about 6ft long 1"diameter 1/8" wall, filled with mercury and a crystal at each end. (What would health and safety say now to the mercury globules in the floorboards?) These memory banks were kept in a cabinet with fan cooling (more servicing!).

Gordon was promoted upstairs to an office job in with Eric Mutch. Vic Claydon was brought in from the Engineering Laboratory. We worked on magnetic-tape drives, and a Mr Willis was interested in a pneumatic drive system and then magnetic tape drives with electric motors.

When the small ferrite rings were used for matrices, we were asked to produce a vibrating pan to deliver them singly and also supply specimen matrices.

Gordon had started to develop a tape reader, which I took over. We removed the mechanical lever movement to make a direct drive and direct brake movement, and then by making Perspex light guides and lenses we were able to read the holes in the tape by using, what was then small, photo electric cells (3/16" diameter?). The aim was to read and stop tape, running at a thousand characters a second, on a row of holes.

Elliotts produced an improved version using an anodised aluminium brake pad. Creeds of Croydon brought out a punched tape printer that ran at a thousand characters per second.

The projects were instigated by academics, research fellows and engineers; names that come to mind are of course Dr Maurice Wilkes, Dr Miller, David Wheeler, Bill Renwick, and David Barron. On the electronic laboratory assistant side we had Sid Barton (and pipe!) and Wilf Waldock (lay preacher); there were 2 others but I forget their names. Temporarily on the mechanical side we had Jim Self (who went off to Manchester, I believe).

John Bennett (Research Student 1947-50)

It was usual in Cambridge for a research student in his first year to provide cheap labour on a project not necessarily related to his thesis topic, and my case was no exception. In my first year, I was responsible for designing, constructing, and testing the main control unit. This unit sequenced the machine through the cycle of extracting from the store and decoding instructions (orders, we called them), extracting operands, initiating individual arithmetical and logical processes, and proceeding to the next instruction. I also designed, constructed, and tested the bootstrap facility.

Don Hunter (Research Assistant 1949-51)

Maurice Wilkes stayed late one evening with a store unit propped on two chairs while testing a gate with feedback he had heard about at an American conference; a narrow pulse examined the squared store waveform in the middle of its timing range and the wider clock pulse held up the output beyond the end of the narrow pulse - phew.

Donald Willis (Research Assistant 1948-50 & 1952-55)

I joined the Maths Lab in 1948 and was assigned to design an 'auxiliary store' for EDSAC to supplement the ultrasonic store. Our first thoughts were to base it on magnetic wire that had been used during the war by war correspondents to record reports from the battlefield. However in order to achieve a reasonable data transfer rate this would mean propelling this thin wire at a speed of eight to ten feet a second, and this was considered too dangerous for use in the computer room. In the mean time someone showed us a recorder based on magnetic tape which had been made by Telefunken for the German army, but there was no available source of magnetic tape. So we constructed a drum which we coated with an oxide material similar to that used on the tape and mounted on it a number of writing/reading stations which were moved to different positions by a lead screw.

Dr Wilkes then fixed me up a job to work with the new group in Sweden, and I returned to the Maths Lab in 1952. In the intervening period magnetic tape of limited quality had just begun to be produced so we decided to build an auxiliary store based on magnetic tape. This required that the 2 thou' thick tape should be accelerated from rest to full speed rather quickly without breaking it. We did this by developing a pneumatic capstan that was able to start and stop the tape at an acceleration of around 50g. The bulk of the tape was held on reels, and these too could be dangerous if static electricity caused the tape to be fed outside the boxes rather than in front of the sensors which controlled the reel servos, as the tape would then be hurled around the room at great speed. An experimental system was run on the EDSAC and Stan Gill wrote the subroutines which interrupted the processor when data arrived from the reading head - a technique which was more widely used later. I left in 1955 to join Decca Radar to introduce digital computer technology into radar systems where we used the interrupt system extensively. Decca subsequently manufactured tape units made on the Maths Lab design and which were used on EDSAC 2, Leo, English Electric and a number of other British systems. Some years later I visited an exhibition of computer equipment in Moscow and was astonished to see a Russian look-a-like using the familiar vacuum capstans and bridge guide to support the tape.

David Brailsford (Nottingham University)

During the three years in which I taught History of Computing to first year students in my department, I used EDSAC (and Martin Campbell-Kelly's simulations thereof) as an approachable paradigm of first-generation computer architecture. I am delighted to report that the hard core of world-weary, seen-it-all-before hackers present in almost all CS classes were open-mouthed in amazement at David Wheeler's Initial Orders 2.


EDSAC 1 maintenance

Don Hunter (Research Assistant 1949-51)

I recall leaving a hot soldering iron directly on the wooden bench and came in next morning to find that Peter Chamberlain had fastened a bit of wood over the hole it had burnt in the bench top.

John Bennett (Research Student 1947-50)

Occasionally some contacts on the EDSAC uniselectors holding the bootstrapping sequence would develop an insulating film. We soon found a quick, if empirical, cure: an appropriately aimed carbon tetrachloride stream from the department's fire extinguisher.

Donald Willis (Research Assistant 1948-50 & 1952-55)

I remember while connecting the experimental tape system to the EDSAC, the door opened and two gentlemen walked in, one carrying a hand-held aerial and the other a portable receiver. It transpired that my equipment was radiating electromagnetic energy (the EDSAC room being on the third floor) and interfering with local radio broadcasting. So I was required to switch off immediately, which did make it rather difficult to identify the cause. However I soon discovered that I had omitted to put in 'grid-stoppers' on to the electrodes of one of the hundred or so valves and this valve was causing the rather long power line which fed +250 volts around the five-foot high rack to oscillate at some forbidden frequency.

Jenifer Leech, previously Haselgrove (User/Research Student 1953-56)

There was a rheostat up on the wall just outside the machine room door, which was used to adjust the voltage if the mains wasn't right. The slider had arrows drawn on it, or on cards - one pointing upwards labelled 'up' or 'higher' or something, and one pointing downwards labelled 'down', or something. One day I put on some other helpful arrows, such as ones pointing left and right, labelled 'left' and 'right', but they had gone next morning. Well, perhaps it wasn't all that funny. One night even the rheostat adjustment wasn't enough and Fred Hoyle, with whom my husband Brian Haselgrove was working on stellar evolution, rang up the electricity board and said "Can you hike your volts up a bit?". I can't remember if they did.

Charles Lindsey (Research Student 1953-56)

Until about late 1955 (early 1956), EDSAC had never worked with its full complement of tanks, so programs were limited to about 800 words. Then, the tanks were cleaned and refurbished and the whole 1,024 words became available.

About that time I wrote a program to simulate the EDSAC on itself so as to detect the length of carries which occurred in actual programs. The simulator occupied 200 words or so. Though it was only a couple of months after the refurbishment, I could only find about 3 working programs under 800 words upon which I could experiment.

D H Shinn (User/Research Student 1947-50)

Although the engineering of EDSAC was as good as it could possibly be, it contained so many components that it frequently broke down. During the daytime engineers were on hand, and rectified such breakdowns as soon as they could. When they left in the evening we programmers would continue running our programs until the next breakdown happened, when we would switch off and go home. However, there was an occasion, probably in March 1950, when EDSAC refused to break down. It continued working throughout the night. When the engineers arrived in the morning they were surprised and delighted to find that they did not have to go through the time-consuming commissioning and testing routine; they just had to wait until the next breakdown! When they came in, I was the only programmer left; the others had gone home to have their breakfasts; I soon went home to have my breakfast, and a good sleep.


EDSAC 1 operating

Jenifer Leech, previously Haselgrove (User/Research Student 1953-56)

The EDSAC 'console' was an old wooden table; when using the machine one could sit with one's knees under it. One hot summer night I was working late, wearing shorts. Sleepily I reached out to the left to put a data tape in the tape reader, and was woken sharply by an electric shock. A little investigation revealed an unprotected rheostat, with mains voltage on it, under the table. My bare knee had been pressing against it.

The unprotected mains had an even more surprising effect on another occasion. As the EDSAC store wasn't very large, some of my programs had 'pending-put' tapes, i.e. output tapes with intermediate results on them which were read in soon afterwards as input for the next stage. The tape punch used to miss out a hole occasionally, and when this was detected on input I used to make the correction using a hand punch which was kept nearby. The punch had once been chained to a table to stop it wandering, but by then it was loose, with the chain dangling from it. One day the usual error occurred, time was valuable, I seized the hand punch, the chain swung under the table, there was a loud bang, and all the oscilloscope displays went out. I can't remember what I put in the log book.

As a research student I became an authorised user, allowed to use the machine alone and switch it off. There was one unbreakable rule - NEVER switch off the 'oven' which kept the mercury memory tanks at a fixed temperature. One night the machine stopped working and I became aware of an ominous smell of burning. I tracked this down to the oven motor, which was dripping oil on to the floor. I switched it off, fearing excommunication at least, but I wasn't held to blame.

There were several levels of machine use authorisation - allowed to use the machine under supervision, allowed to use it alone and switch it off, and allowed to switch it on. Plus one unofficial higher level - to achieve enough confidence to turn J.C.P. Miller off the machine when his time had run out and it was one's own turn. I think I reached that level in the end.

There was a story about someone (Sandy Douglas?) going to sleep for several hours one night while the machine worked on (sometimes it did!), producing tape output. The sleeper woke up to find a cleaner tearing the night's work off the tape punch and throwing it away. I don't know if it was retrievable.

John Bennett (Research Student 1947-50)

I remember an April Fool's day prank from that time. Someone (possibly David Wheeler) arranged a surprise for one of our colleagues, Ken Dodds, by inserting one extra hole in the paper tape containing his program. This hole had the effect of transferring control to instructions that had not been cleared from the EDSAC store. We had a problem because the queue to use the machine was particularly long that morning. However, one of us made a grand gesture and surrendered his place to ensure that the doctored program would run before noon, as was required by the April Fool's Day ritual. It worked like a charm. Our EDSAC program printed out: "Ease up Ken, I've been working all night. EDSAC." Our colleague was not amused!

Don Hunter (Research Assistant 1949-51)

Was it Alec Glennie who made EDSAC print a message "Hey, I'm tired, I've been working all night" when the operator started it? There must be more to it than that because pressing the start button would always cause the same effect.

Peter Wegner (Diploma Student 1953-54)

Mastering the Initial Orders of EDSAC 1 was a rewarding and aesthetically fulfilling experience. This 50-instruction program was bootstrapped at start-up time and provided programmers with a sophisticated machine language with relative addressing. The initial orders were put together in an incredibly clever way to minimise space. We were very conscious of space limitations during, having only 512 36-bit words of mercury delay line memory.

Mike Pitteway (Research Student 1956-59)

I was a fully-authorised user of EDSAC 1 in 1956, then EDSAC 2. My wife, Cynthia used to sit up on Friday nights with me and EDSAC 1, knitting in the middle of it to keep warm1 (there was a chair in the space once occupied by a rack of valves). She wasn't so keen on EDSAC 2, feeling that "it lacked character". Peter Swinnerton-Dyer ran the early evening session, then David Barron and I for the rest of the night, subject to breakdown.


EDSAC 1 applications

John Bennett (Research Student 1947-50)

The rest of my time at Cambridge was spent learning some mathematics and working on the computerisation of various engineering computational procedures for my thesis. I devised one programming technique that was probably a first - the use of an interpretive scheme. My reason for using the interpretive technique at that time was to save space in solving a differential equation using the Runge Kutta process. EDSAC had a small store by modern standards (initially 256 36-bit words most - but not all - of the time and no backing store), so every bit was important.

Robin Stokes (User/Research Student 1948-49)

I was a Ph.D. student (Pembroke) in physical chemistry in the Free School Lane laboratories in 1948-9. My work involved a good deal of calculation such as numerical integrations, and I was the fortunate owner of my own mechanical calculating machine, a Marchant of about 1920s vintage which is still in working order.

D H Shinn (User/Research Student 1947-50)

I started research in the Cavendish Lab in 1947 in the group run by Mr J A Ratcliffe, which was concerned with the propagation of radio waves in the ionosphere. In 1949, I gradually became aware that there was a machine called EDSAC in the Maths Lab which would help me in my investigations. I started learning about EDSAC and writing my program in December 1949. The development of even the simplest program then took quite a long time, and I obtained the first solid results from the program in February 1950.

I obtained the first really useful results just before Easter 1950, and carried on developing these in the summer. As my last activity in Cambridge in September 1950, I married Jean in St Edwards Church. We had our Wedding Reception in the Lion Hotel in Petty Cury, which was shortly afterwards pulled down to make room for a large new development.

The results which I obtained from EDSAC were incorporated in my thesis, and published in the Journal of Atmospheric and Terrestrial Physics. I think that I obtained my PhD degree not because of the quality of my mathematics or physics, but because my thesis was one of the earliest which incorporated the results of a computer program; I don't think that my examiners understood much about computer programs! I have spent the rest of my working life with radio waves and antennas. This has been exciting, and much helped by three significant inventions which started between 1949 and 1957, namely transistors, satellites, and, thanks to Maurice Wilkes etc, computers.

Jack Harwood (User/Research Student 1949-50)

Between 1947 and 1950 I was a research student at the Cavendish, studying the propagation of low-frequency radio waves through the ionosphere. Part of the work involved taking simultaneous pen-recordings of the varying signal amplitudes received at two stations a few kilometres apart, and then calculating correlation coefficients between these for groups of a hundred or so paired readings. The computations involved lining up the two columns and calculating sums of squares and cross products, then repeating this for about 20 relative vertical shifts of the two columns.

I wasn't sure at the time whether Dr Wilkes had a program already written for performing these calculations, or whether one was specially written for the purpose but looking at the reproduction, on your web site, of the log entry for 1949 May 6, it looks like the former, and my work must have come up not a lot later than that first entry, as my period at the Cavendish ended in mid-1950.

Anyway, the outcome was that Mr Ratcliffe arranged for me to be invited over to the Mathematical Laboratory, where I spent several happy hours typing the data onto punched tape, and then was helped to feed these rolls into a reader attached to the big machine itself. If I remember correctly, it took about 10 minutes for the a tape's data to be fed through the mercury delay tanks and the EF50s and come out with all the summations, and I was very pleased with the final results and the effort it had saved.

The assistance given by Dr Wilkes and the Mathematical Laboratory, by the way, was acknowledged in my eventual PhD thesis in 1951 and in a subsequent IEE paper published in 1953.

Don Hunter (Research Assistant 1949-51)

I still have a ribbon (tweeter) loudspeaker horn calculated on EDSAC because I did not know the closed form of the solution giving the shape of the sides. These were bent on the metal rolling machine by Bill Renwick, presumably during the lunch hour.

Leonard Dresel (User/Research Student 1949-52)

I was a regular user of EDSAC 1 from 1949 to 1952 as a postgraduate student under Dr S.F. Boys, and I contributed the subroutine V1 published in the book by Wilkes, Wheeler and Gill in 1951. I also served as a demonstrator on the programming Summer Schools held in 1950 and 1951.

Geoff Cook (User/Research Student 1951-53)

Colin Reeves (User/Research Student 1952-55)

In the early 1950's, all the user groups around the EDSAC were enthusiastic about exploiting this new tool within their different disciplines none more so than the theoretical chemists under the leadership of Dr Frank Boys. He had many deep insights. One of the most significant was that computer usage was not confined to large-scale arithmetic operations but could also encompass algebra together with a range of symbol manipulations. Thus the EDSAC was used to generate automatically the complex formulae (some consisting of hundreds of many-variable terms) for the three-and six-dimensional integrals that are required in fundamental quantum-mechanical calculations of molecular structure. The computer representation of these formulae was used directly in the subsequent evaluation of the integrals for a particular molecule under consideration.

We are very glad to have participated in some of the first fundamental calculations of molecular wave functions and remain grateful for the facilities that were provided by the Mathematical Laboratory.

William Cochran (User 1946-64)

From 1946 to 1964 I was a member of the Crystallography Group in the Cavendish Lab and an intermittent user of EDSAC 1. Sometime in the mid-1950s, A.S. Douglas and I published in Proc. Roy. Soc. a method for the direct determination of crystal structures using EDSAC. As far as I know it was the first such proposal for the use of a computer for this purpose. I must admit that in practice it was not very successful as it was beyond EDSAC's capabilities. Later others were very successful using related methods, particularly a former colleague, M.M. Woolfson, also an EDSAC user, and who retired as Professor of Theoretical Physics at York University not long ago.


EDSAC 1 people

Don Hunter (Research Assistant 1949-51)

Bram Loopstra from the Matematisch Centrum in Amsterdam spent three months or so at the Maths Lab and returned from a visit to NPL gleefully waving a Pilot ACE chassis.

Neil Breakwell (Undergraduate 1948-49)

It could have been 1948 or 1949, when I was a Selwyn undergraduate reading for the Natural Sciences Tripos, that I was given a guided tour of EDSAC and its racks of valves and other components, and also shown the small (separate) differential analyser, by the then operator of EDSAC, a young mathematics graduate from Pontefract, West Riding of Yorkshire named Eileen Emily Caroline McKee, whom I subsequently married.

Don Hunter (Research Assistant 1949-51)

Someone tried to convince Eileen McKee that there was a mouse in the paper tape bin.

D H Shinn (User/Research Student 1947-50)

We all owe a great deal to Maurice Wilkes. I also remember with gratitude David Wheeler. He spent a fair amount of his time in 1950 writing and testing subroutines for the rest of us to use; we couldn't possibly have managed without his subroutines. Another programmer whom I remember well is Tony Brooker. He came to Cambridge in order to work on a machine called a Differential Analyser. This machine could be described as Wheels Within Wheels a remarkable achievement in precision mechanical engineering, designed to provide analogue solutions to differential equations. Tony, being a bright lad, soon discovered that EDSAC was a much more effective tool for dealing with differential equations, and abandoned the Differential Analyser. He later became a professor at Essex University. Also working on the EDSAC in 1950 were Francis Crick and John Kendrew from the crystallographic department of the Cavendish Laboratory. I had no idea then that their work would become so important for absolutely everybody. They, like all the other programmers, were very pleasant people to deal with. And we must not forget J.M.M. Pinkerton, who went to work for the caterers J. Lyons on the commercial applications of computers; that subject has advanced quite a lot in the last fifty years!

George Felton (Undergraduate 1946-51)

When I was a maths student at Cambridge in 1946-51, I attended numerous Thursday colloquia in the Mathematical Laboratory and followed the design and construction of EDSAC with intense interest. I got to know Maurice Wilkes, David Wheeler, Stan Gill and many others.

I continued to attend colloquia after I went down, when I was employed at Elliott Brothers, and later Ferranti and ICT/ICL, on the design and programming for the Elliott Nicholas Computer, Pegasus, Orion, 1900-series (where I was responsible for the George Operating Systems), planning the ICL 200-series, etc.

Donald Willis (Research Assistant 1948-50 & 1952-55)

Dr & Mrs Wilkes traditionally hosted a Christmas party for the children of staff and a number of sketches were provided for entertainment. One of these, in around 1952, was a parody on a popular BBC programme of the time for children entitled 'Listen with Mother' which began with the words "Are you sitting comfortably? - Then I'll begin." The sketch was, of course, called 'The Microprogramme'.

Charles Lindsey (Research Student 1953-56)

Sid Barton and Wilf Waldock were the Departmental Matchmakers, and regarded the marriage of Eric Mutch and Margaret Lewin as their crowning achievement (though they admitted that Sylvia (Rossiter) and myself managed perfectly well without their assistance).

Jenifer Leech (previously Jenifer Haselgrove) (User/Research Student 1953-56)

I was in the Maths Lab working on EDSAC 1 in 1953-56 as a research student in the Radio Group of the Cavendish Laboratory, also doing some part-time work for them. My first husband, Brian Haselgrove, was a Senior Assistant in Research in the Maths Lab at the time, and John Leech, later my second husband after Brian's death, was a research student. Brian had done some vacation work as an undergraduate towards the building of EDSAC (an unsuccessful attempt at a piece of test equipment, I believe), perhaps John too. My son, Richard Haselgrove did the Computer Science Diploma in 1973-74.

Mike Pitteway (Research Student 1956-59)

We both got to know Eric Mutch well. I remember his sister (or was it his sister-in-law?) at one of their parties wearing nothing but an un-stitched roll of cloth to win a bet. She made it without impropriety (just).

Also a night when Peter Swinnerton-Dyer introduced us to the music of Tom Lehrer during an EDSAC party. There were the remnants of an unfinished barrel of Greene King, and the engineer (Bill, if I remember rightly after all these years) agreed to barrel sit, and I returned early Sunday morning to be greeted by the soft sounds of distant singing.

Oliver Wintringham (Decca Radar)

Perhaps the most surprising thing about EDSAC, for me, is that I did not hear about it, nor suspect its existence, while reading Mechanical Sciences (with a part II in Electronics) from 1949 until 1953. I was actively looking for a branch of Engineering that would be as interesting as the Army (where I had studied digital radar equipment and selsyns) was, but I nearly missed computers, since neither I nor the Appointments Board had heard of them!

I am pleased to say that I have been working as a computer engineer, on hardware, systems and software, ever since.

Peter Gray (Undergraduate 1958-61)

I was a Cambridge undergraduate in Natural Sciences who actually ran his Xray practical data though EDSAC 2 in 1961, got hooked, did a PhD in high energy physics with computing, and has been computing ever since.


EDSAC Summer Schools


Durward Cruickshank (Summer School 1950)

In September 1950 I was appointed Lecturer in Mathematical Chemistry in the University of Leeds. As my first task, my boss Professor E. G. Cox sent me to the Cambridge Summer School on Programme Design for Automatic Digital Computing Machines. I believe this was the world's first summer school on electronic computing. Cox led the chemical crystallography group at Leeds. He had been a pioneer from 1937 onwards of X-ray structure analysis by Fourier methods with three-dimensional data. The Leeds laboratory was strong in computing by punched-card methods. Cox was keen to exploit new ways for handling ever-larger crystallographic calculations.

My recollection of the ten-day School is that there were some 20-24 participants of varying seniority. We were given the September 1950 issue of the Report on the preparation of programmes for the EDSAC and the use of the library of sub-routines. I still have my copy and also my manuscript notebook. It shows lectures on the following topics. To indicate the relative sizes, I show in parentheses the number of my pages on each topic.

D. R. Hartree: Numerical Analysis (15 pages)
S. Gill: Programming (21)
R. A. Brooker: Logical Design of the EDSAC (5)
D. J. Wheeler: Sub-routines (13)
S. Gill: Checking Routines (4).
Evidently numerical analysis was considered a pre-requisite to good programming. There were two external speakers J. N. Wilkinson: Programming for ACE (3)
T. Kilburn: Programming for the Manchester Machine (6).
The final General Discussion opened with a description by M.V. Wilkes of developments in the USA (3 pages). The participants by then had realised how splendid was the success of the Cambridge team in bringing EDSAC into working operation in 1949.

I have lost my copies of the programming exercises we were given. By the end of the School some of the students were running their own problems on EDSAC. One Dutchman found that a certain 20-decimal number was factorisable. He was lucky. He got the first factor in 15 minutes. If the number had been prime, the run would have taken 12 hours.

One student who made no attempt to do the exercises was B.V. Bowden, who had done his Ph.D. in Rutherford's lab and was now computer salesman for Ferranti. Vivian's objective in the exercise periods was to chat individually to the participants about the computer Ferranti was building in Manchester. This was the commercial version of the first electronic stored-program computer, built and run by F. C. Williams and Tom Kilburn in 1948 using cathode-ray storage tubes.

I owe a double debt to the 1950 Summer School. It introduced me to the principles of computer programming, machine order codes, binary arithmetic etc. Through Bowden the School introduced Cox and myself to the Manchester project. From 1952 to 1957 the Leeds crystallography group made very heavy use of the Ferranti Mark I computer. When Leeds University bought a Ferranti Pegasus in 1957, it chose Sandy Douglas from Cambridge, also a participant in the 1950 Summer School, as its first Director of Computing. In 1967 Vivian, by then Lord Bowden and Principal of UMIST, invited me to move from Glasgow to Manchester.

Dick Grimsdale (Summer School 1950)

I attended the Summer School in Programming in 1950 and wrote my first program on the EDSAC 1. From 1960, I was working on computer developments in Manchester and in those days the community was very small and so we all knew each other.

Edsger Dijkstra (Summer School 1951)

My memories of my visit to the programming course in September 1951 are mainly non-technical: this trip was my first visit to a foreign country and as such it was an overwhelming experience.

In Cambridge I lived in a student house with about 30 rooms. In a letter to my parents I described the landlady as 'an angel', but I remember that when I came home I had to play the piano and then to accompany her while she sang. It took me some time to realise that usually she was slightly drunk.

I also remember an early Sunday morning when I realised that I had eaten my (still rationed!) bacon raw, and that I should not have done so as it might be trichinous. (During the war we had been warned for that possibility.) I still see myself walking through the cool, still deserted streets of Cambridge until I had found a hospital, where I told the person I encountered "I might be poisoned". When I had gone in a little bit more detail, I was told that English bacon was safe....

Once when Wilkes was lecturing, he wanted to show an example and asked the audience to choose between the calculation of a definite integral and the numerical integration of a differential equation, but the British audience was too polite to push its preference. I had a preference because I was not too sure what differential equations were; deciding to break the deadlock I said in my best English "I feel like a definite integral". Wilkes spontaneously reacted with "Well, you don't look like it!" and everybody laughed; Wilkes immediately corrected himself and added "What you said was perfectly all right, only we don't say it."

I also remember the lecture by Tony Brooker who had been invited as guest speaker. In the academic environment in which I was growing up, I had never heard a Dutch speaker lecture with a regional accent; this was simply not done. You can imagine my consternation when I was exposed to a lecturer whose accent was so strange and unfamiliar that I could hardly understand him! (From the lecture I don't seem to remember much more than that he used lots and lots of slashes //////.) Eventually I asked my neighbour whether he knew to what kind of English we were exposed; he listened carefully for a short while and said, "My guess is 16 years of Manchester superimposed on 16 years of cockney." I felt vindicated. I never checked it.

My greatest scientific excitement was probably caused by the subroutines E2 (for the exponential function) and L1 (for the logarithm), E2 because it was so ingenious, and L1, because it was so simple and such an eye-opener. (It still is.)

Because my father was quite familiar with Hartree's work, the latter is mentioned in a letter to my parents. In that letter I found that the participants were split into groups of half a dozen or so, and that I was not in Hartree's group, but in Wilkes'. I wrote my parents that one day Wilkes remarked to me "Ah! You are a bright boy!" In retrospect, I think that the general consensus is that, once more, Wilkes had been right.

It is no exaggeration to say that those three weeks in Cambridge changed my life!


Diploma students in the 1950s

Peter Wegner (Diploma Student 1953-54)

In the spring of 1953, I was completing my BSc degree in mathematics at Imperial College when Douglas Hartree gave a visiting lecture and persuaded me to come to Cambridge for the summer. I worked with him on a problem that involved collaboration with Peierls in Birmingham and the two young physicists Jerry Brown and Sheila Brenner. This problem involved solving differential equations with Bessel function right-hand sides by the Runge-Kutta-Gill method. I was able to simplify the solution procedure by representing the Bessel functions by differential equations rather than tables, solving a larger set of differential equations without the need to resort to tables and interpolation. The idea of replacing laboriously computed tables by differential equations seemed counter intuitive, but simplified and speeded up the solution process.

One of my early assignments was writing a program for solving linear equations. I was fascinated by the ability to look at the memory content while the computation was progressing and watch successive data values being zeroed as a part of the elimination procedure. I was sloppy in providing test data for the equation-solving program and ran my first test with two identical rows, which should have caused the program to crash on division by zero. However, round off error came to my rescue and I watched the program divide by 2**-35 and provide a solution of rather large numbers that, on back substitution, provided a satisfactory solution to several decimal places. Thus, I was able to successfully invert a singular matrix.

Our first Diploma class in 1953-54 consisted of three students. The other two were Albasini, who subsequently worked in the national Physical Laboratory on numerical analysis, and Stan Bootle, a colourful married student with a family of five children whose door was always open to my visits, and who later became quite a well-known radio personality.

I still have my diploma thesis, with over 100 yellowing pages that include chapters on the Initial orders, the differential equation problem, and philosophical chapters on computation, which are dated but include a discussion of software complexity, systems with multiple interfaces, and other topics that later became important areas for technical analysis

Maurice Wilkes had a strong influence on my intellectual development. Recognising my inclination towards philosophy, he asked me to look into the work of Leibniz on early calculation, and I translated an article by Leibniz from German into English. I have greatly valued my continued contact with Maurice over the years, meeting with him several times a year during his years in Boston working for DEC.

Cambridge was an exciting place in the 1950s. I organised a small philosophical study group with Amartya Sen, who recently won the Noble prize in Economics for his work on world hunger. I often went to tea at the Cavendish Laboratory, where they sold delicious cakes for two pence each, and attended the quantum theory lectures of Dirac. In the evenings I often ate at the local ABC restaurant and remember having dinner there with Francis Crick on a couple of occasions. On one occasion, I was "progged" by a bulldog and two proctors for not wearing a gown after dark. I had to pay thirteen and four pence because I was a graduate student (the fine for undergraduates was six and eight pence). I lived in an attic in the vicarage at 45 Jesus Lane, right opposite the entrance to Jesus College.

My short, one-year stay, at the Maths Lab played a key role in my professional life whose importance I am only now beginning to appreciate. After Cambridge, I spent a short time in Manchester working with Brooker, and later became a part of the brain drain, working on time sharing at MIT, returning to the London School of Economics to work on operations research, and then back to the USA to work on programming languages, semantics, and software engineering.

Christopher Phelps (Diploma student)

I was one of the users of EDSAC 1 when it was in its youth and when, I think, Jenifer Haselgrove was trying to make a tape unit work. I took the Diploma course and still have a copy of the dissertation I wrote, supervised by Sandy Douglas, about cyclic solutions to ODEs. I used EDSAC routinely, that is to say every normal working day (as students do).

Diana Belcham (Diploma student 1956-57)

In 1956-57, I was the only female Diploma student (as Diana Catton). One outstanding memory of the year is the encouragement of my tutor, J.C.P. Miller. The Diploma was a stepping stone to a generally enjoyable career in computing.



EDSAC 2 construction

Charles Lindsey (Research Student 1953-56)

Maurice would come in, see that the power was on and say: "Oh, good! I see we are making progress!".

Bill Renwick would come in, see that the power was off, and say: "Oh, good! I see we are making progress!".

(The point being that the bug last found when the power was on had been identified , and was now being fixed).

Oliver Wintringham (Decca Radar)

I was in the team at Decca Radar, under Donald Willis, that made the Decca Twin Tape Unit. The technology had been developed at MIT and then in the Cambridge Mathematical Laboratory and the first magnetic tape unit from our production line was sold to Cambridge, to attach to EDSAC 2.

In 1957, or perhaps 1958, I arrived with the tape unit, to see it safely installed upstairs in the Mathematical Laboratory, on Corn Exchange Street. It was the size and weight of an upright piano, so we were grateful for the help of several Maths students who also rowed. They manhandled it up the Gothic staircase.

Magnetic tape was an exotic new peripheral then and this was the first drive available in the UK. Our market place, outside the universities, was the eleven competing UK computer manufacturers (Leo, Ferranti, English Electric, Vickers, British Tab. and so on).

In some conditions, the magnetic tape clung to the metal guides, and was damaged. On my second or third visit, I brought a message to the Mathematical Laboratory: "Try boiling a kettle, to increase humidity, and so reduce static". I was sent back, with a message to Decca Radar: "At that price, we expect to find the kettle built-in".

Peter Toye (Archimedean 1963-66, Diploma Student 1966-67)

A reminiscence that Eric Mutch told me, not long before his death.

When they were installing EDSAC (I think 1, maybe 2), he commented to the engineer who had been responsible for the strengthening of the building that he hoped that the building would take the weight. The engineer responded, saying that he'd multiplied Eric's weight estimate by 10 before doing the specification. Eric's comment was "That should be all right, then. I multiplied mine by 10 before giving them to you."


EDSAC 2 maintenance


Roy Bayley (Computer Engineer 1962-73)

The late Eric Mutch hired me to work on the Titan commissioning team so I have little experience of EDSAC 2. However, I did help out on EDSAC 2 from time to time and I found it a scary machine. In fact, my earliest memory of the Maths Lab involves being present when an EDSAC 2 unit burst into flames. This apparently was a common event and Peter Bennett calmly reacted by using a fire extinguisher to put it out.

For those unfamiliar with its layout, working on EDSAC 2 could be dangerous. The machine had many bare terminals and wires carrying up to 350 volts. You needed to be very careful where you put your hands and preferably keep one hand in your pocket!


EDSAC 2 operating

John Lindley (Diploma Student 1958-59)

Elizabeth Waldram (User 1959-65)

The loudspeaker enabled you to listen to the progress of your program and, in particular, to detect the dreaded 'closed loop'. A repetitive pattern alerted the other members of the queue, and it was then a question of how long you could endure their quizzical glances, before admitting defeat and retiring to try and sort out your code in time for the next test period.

Peter Fellgett (User 1962-65)

Being a valve machine, EDSAC 2 would fail every few hours. The daily routine was that the engineers kept it working during normal hours, after which it was available for use so long as it remained serviceable, which might be after a half an hour or so, or else extend into the small hours. There were two classes of users, "fully authorised" who could be in sole charge of EDSAC 2, and "semi authorised" that could use the machine in the presence of a fully authorised user. At night, we used to congregate on the EDSAC 2 floor and sit on the rather with-it studio couch that was there. There was always a bit of tension about whose turn it was, but this resolved when Teddy (Sir Edward) Bullard turned up and asked a few questions about what order we were in. He was a great personality.

There were (I think) three program-testing periods each day, each of 10 minutes duration. We would queue to feed our program tape into the reader, and the most usual result was the dreaded report-stop. If you tried to call a non-existent order, call an unset modifier register, overflow the accumulator, or try to take the square root of a negative number, etc. a precise machine-action had to follow, usually the report stop. This was irreversible, and printed out a little diagnostic information such as the store-location of the order causing the stop, the content of the accumulator, etc. The social pressure to get off the machine quickly was of course enormous. You then tried to find the error in your program, correct your tape, and go back for another go. Some people achieved as many as three tries in the 10-minute period. People today who program by clicking a mouse really do not know what life is about!

An abiding memory is of a woman emerging from her office and declaiming to the assembled multitude: "I want a man, with long strong arms." It emerged that she had lost a program tape down the back of a heavy desk.

Judy Thomas, formerly Bowers (Operator 1961-67)

There were frequent fires in the valve chassis and I always wanted to reach the fire extinguisher first but never made it, the engineers arriving before me. The smell was quite unique; as soon as one entered the building one knew the computer would not be working and there would be the notice at the top of the stairs - M/C OFF Come back in so many hours. One fire destroyed the ferrite core store and EDSAC 2 was down for weeks. We (the operators) had to help the engineers wire these ferrite cores back again - very fiddly and it took hours (days in fact). Sid never did allow us to solder them back onto the boards (that would have been much more fun).

There were certain times in the day when students and staff operated the machine themselves. There was a queuing system whilst we operators had our morning coffee and afternoon tea on the floor below. Otherwise, we ran their programs ourselves: short ones first followed by the longer ones hoping they wouldn't fail whilst we did other things. The evenings and nights were booked for even longer jobs that users ran themselves.

Philip Ekstrom (Diploma Student 1963-64)

After a virtuous beginning on the antique Brunsvegas, and since Atlas was still not ready for our use, practical computing centred on EDSAC 2. We prepared punched paper tapes with our programs and data on them, queued up in front of the console, and waited as the operator fed each of our tapes into the reader. We would collect the resulting output tape (if any!), find a free teleprinter, and print out the results. I recall a contest among several students to produce the shortest self-replicating tape.

By then a 'backing store' of 16K words had been uneasily grafted onto the machine, so the original 1K memory limit was eased for data, though programs could still be executed directly only out of the original 2K (half-word instruction) store.

Being familiar with contemporaneous American computer technology, I noted several differences of style. Magnetic tapes at home were simpler media written sequentially in contrast to the block-addressed tapes I encountered at Cambridge. The electronic technology in EDSAC 2 (soon to be turned off) was by then old, but its design seemed to me extremely clever at getting the greatest possible performance out of a minimum in hardware. Especially appealing were the routines in "fixed store" which had a great deal of sophistication compressed into a very few instructions and using very little workspace. They let the machine come up much smarter and friendlier than any I had previously seen.

Karen Sparck-Jones (User1964 Reader now)

I was around the Lab during most of EDSAC 2's time, though I was not myself a user (I had some experiments using EDSAC run for me by Roger Needham).

The second floor area where the operating console was had a definite character, especially on the evening and night shift, combining earnest dedication and cheerful camaraderie. The evening rota dated June 1962 which survives includes e.g. Birch, Bullard, Swinnerton-Dyer and Wheeler for Thursdays, Matthewman, Mutch and Needham for Fridays. The central part of the room, with the console, was surrounded by a raised walkway and offices. There was also the 'user area', from which the well-known 1960 photograph was taken. This alcove was furnished with the user name queue, a home-made gadget into which users fed their name tags to claim their operating turn; a large grey and red sofa; and stacks of miscellaneous non-computing reading material including science fiction and the Memoirs of Lady Knightley of Fawsley, a member of the Victorian gentry and luminary of the Girls Friendly Society. Though the sofa was quite restful, the user area was definitely deprived by modern standards, since there were no vending machines.

Rachel Wroth, formerly Britton (Diploma student 1965-66)

My earliest memory of the Laboratory was the funeral of EDSAC 2. A room full of people, many dressed in black, a wreath made from paper tapes, a funeral oration and the last post I could not understand why so many around me were reacting so emotionally. As a newcomer, I had never used that machine and thought it was just a rather ugly large piece of laboratory equipment. I soon came to realise why so many had become so attached to it and how important its development was to the future of computing.

Richard Jennings (Diploma student 1962-63, Ferranti)

I wrote a Music Compiler for EDSAC 2 which was used at the close down ceremony for that machine. I have some old (reel-to-reel) tapes of earlier runs of some of the music used on that occasion, which I hope to transfer to cassette early next year.


EDSAC 2 applications

Elizabeth Waldram (User 1959-65)

There were computer graphics before 1965! I wrote some of the very early graphics software on Edsac2 (1961-62) for displaying and photographing radio-astronomy maps on the cathode ray tube, which was then the fastest form of output. The plots were essentially 'slices' through the sky brightness distribution and preceded the early contouring algorithms on which I also worked.

Peter Fellgett (User 1962-65)

Looking back, one sees what an enormous conceptual advance EDSAC 2 represented in being a binary general-purpose machine. Many people at the time had great difficulty in getting their minds around the idea of a machine whose internal structure would be unaltered whether it was finding prime members or doing Fourier transforms. Surprisingly, probably because appreciation of the problem went down to a lower level of imagination, many people seemed to have even more difficulty with the idea of a machine working in binary. Machines were built at this time with hardware radix 10 arithmetic, and even hardware variable radix to deal with the arbitrary radices of pre-decimal currency and Imperial weights and measures. Being dyslexic, as there is evidence Alan Turing was, may predispose against this raid of error.

Fortunately, EDSAC 2 users were spared two of the major incubi of computing, FORTRAN and punched cards. We programmed in clean machine instructions, what would now be called assembly language although to logic of not calling this machine language is dubious. With 1,000 ch/sec readers, punched paper tape was an excellent medium, cheap, compact and perhaps above all robust. One user successfully read a tape he had accidentally sent to the laundry in the pocket of his shirt, whereas the slightest scuffing of the edge of a card could spell trouble. Moreover with tape, you cannot drop the deck of cards.

With a core-store of 1K words and a time for floating-point multiplication of (I think) 250 microseconds, great store was set by economising orders. There was a saying that given any program, David Wheeler could do it in fewer orders. This might seem to lead by iteration to an absurdity, but to anyone who had seen what David could do to a program, the absurdity was far from obvious. A machine with such a small store and slow speed might seem almost unusable to today's prolix programmers, but it opened up fields of investigation which had hitherto been inaccessible.

Not the least of these new fields was the extension of X-ray crystallography from simple inorganic crystals to large organic molecules, leading in the hands of Perutz, Kendrick, Franklin and others to the elucidation of the structure of DNA. X-ray crystallographers were not however over-popular with other users since their programs were output-limited. The machine was thus tried up for much time acting as nothing more then a computer for a printer or punch.

After I left Cambridge to go to Royal Observatory Edinburgh, I was allowed to continue to use EDSAC 2. I made one visit hoping to run a small job, and as I walked into the Maths Lab was greeted by Eric Mutch who said: "Oh, hello Fellgett! Do you know we have an Autocode now?" and he handed me the book. So I sat down to read it, and within half an hour had successfully run my job. A moral of this, I suggest, is that something is lost (as well as gained) as soon as we begin to teach anything. If, instead of getting down to it on my own, I had been taught the EDSAC 2 Autocode, it would have taken a 10-lecture course. In these days, high-level language was known as automatic programing.

One slight regret is that in my days the EDSAC 2 library never included a geometrically precise routine for Fourier transforms, one which when applied twice would deliver the original ordinates back again (but in reverse order) free from the loss of orthoganality occasioned by "apodization" or other messing about.

Roger Stratford (User 1963-71)

My connection with the Lab started in 1963 when I worked for a small organisation called Schaefer Dielectrics. I used to bring the job and data tapes over to the Lab and collect the output from previous runs - I assume it was the EDSAC 2, though I never saw the jobs being run. The jobs were to generate calibration data for a microwave dielectric-measuring instrument.


EDSAC 2 people

Ruth Loshak, formerly Feinstein (Programmer 1958-60)

I worked as a programmer on EDSAC 2, from 1958 to 1960. I shared an office with Margaret Mutch for some of that time.

I remember my days at the Mathematical Laboratory with great pleasure it was a great shame that in those days you were expected to stop working when you had a baby otherwise I might still be working with you. A gap of a few years made it hard to get back into the computer world, though I did work for a time with Roy Wisbey at the Literary and Linguistic Computing Centre. However I went into teaching first of all teaching Russian (I had learnt it on the job translating a book about the BESM computer for Prof Wilkes).

Peter Fellgett (User 1962-65)

The staff of The Mathematical Laboratory were the guardians of what was for those days a very large, expensive and powerful facility, yet my overwhelming memory is of their friendliness, helpfulness and welcome. This is not to say, of course, that fools were suffered gladly. There was a Priorities Committee that vetted jobs proposed to be run on the machine. This no doubt did a useful job in improving ill-considered proposals, but I never heard of anyone actually being rejected. According to Peter Swinnerton-Dyer you had to be both stupid and arrogant, neither alone would do it.

Judy Thomas, formerly Bowers (Operator 1961-67)

I arrived at the Mathematical Laboratory (as the lab was called then) in August 1961 as a naive 18-year-old straight from A-levels at school. A computer: goodness, what was that! Paper tape, magnetic tapes - I was quite bewildered. School had taught me nothing about these. I was used to Log tables and a slide rule - not even a calculator. To see Dr J.C.P. Miller on his Brunsvega hand machine was amazing; how did he turn the handle so quickly? However, I soon settled into lab life with the help of Eric Mutch, Valerie and all the Engineers - Sid, Ken, Pete, Wilf, and John plus others. As an operator, I was allowed, in fact encouraged, to attend some of the Diploma students' lectures and so became a little au fait with machine code and later Autocode.

Everyone was very friendly and, socially, I was always very busy. My poor Mother was used to me telephoning home to say I would be missing lunch (off to the Mill) or would be late home for tea (off to the Eagle for a pint). Then there were the punt outings with lab staff and students during the summer afternoons - we couldn't all go, as someone had to look after EDSAC 2! I also remember the annual sherry party.

Harold Gearing (Metal Box Company)

I was joint founder-editor with the late Eric Mutch of the Computer Journal and attended in Cambridge for quarterly meetings up to 1968-69.

Though I attended an EDSAC programming course at Northampton College (now City University) given by Mac Bridger and Eric Mutch, I never actually ran a program on the machine.

Stephen Parry (Diploma Student 1966-67)

As a student of the first year of the Diploma in Computer Science (1966), I still have vivid memories of Messrs Wilkes, Needham, Barron, Wiseman, Matthewman, Miller, and others. What stars!

Richard Parkins (Undergraduate 1965-66)

I used EDSAC 2 at the beginning of my undergraduate career using facilities provided for the Archimedeans' Computer Group. My first program was written in EDSAC Autocode, and it calculated and printed out the prime factors of an input number. Much to my surpise it worked first try, which is probably what hooked me on computers as a career.  I don't think I have repeated that sucess since.


Diploma students in the 1960s

Philip Ekstrom (Diploma Student 1963-64)

I came up in 1963 for the Diploma Course at the instigation of Norman Sanders, an earlier student in the course. He was by then running the Computer Methods group at the Boeing Company in Seattle, I was an undergraduate who had worked for him two summers, and he had decided that someone should EDUCATE this brash young fellow.

My undergraduate degree was in Physics, with a few courses in Numerical Analysis thrown in. I had experience with the IBM 709 in assembly and Fortran, and some background in electronics. With that preparation, student support for a year of computing preparatory to a programme in Physics, and a new wife beside me, off I went on my first trip across an ocean.

One surprise at the Mathematical Laboratory, as it was then called, was a level of mathematical preparation in my fellow students higher than I had found at home. Another was the breadth of the programme. One lecture might be on classical numerical analysis, perhaps followed by a practical session on interpolation with Brunsvega barrel-style hand-cranked mechanical calculators. Another might cover compilation techniques, and still another might be a report on the tunnel-diode logic work then underway at the laboratory. I recall describing the programme later as "...designed to give you the mistaken impression that you could design a computer from scratch, build it, and program it to do anything." The impression would be mistaken only in that what you had been taught was how to start on those tasks and where to look for what else you would need to know.

Much of my work with computing has in subsequent years centred on small-embedded controllers, often part of miniature or inexpensive field data collection devices. In many cases they gain performance from including in the field instrument the capability for an unusual amount of autonomous action. I find that many of the techniques and points of style learned then, both from and on a world-class (if ageing) central computer, go very well with today's $10 control processors.

Peter Toye (Archimedean 1963-66, Diploma Student 1966-67)

The program in the programming class which took an unprecedented 20 seconds to run before crashing (most of our programs failed in microseconds). It turned out to be sorting the array it was given, running off the end, sorting the rest of memory, wrapping round the top, and sorting itself into order before hitting the data that it had inserted into itself.

Returning late one evening to the diploma students' room, seeing a light on and hearing noises. On entering, finding Dr J.C.P. Miller working a manual Brunsvega calculator completely engrossed in his calculations, not noticing me at all. Fingers moving at the speed of light - I could work out some of the short cuts he was making, others left me baffled. It was rather like watching Paganini practising.

Rachel Wroth, formerly Britton (Diploma student 1965-66)

I had arrived in Cambridge in October 1965, with a physics degree and after a summer at CERN, the nuclear physics centre in Geneva, where I had attended an intensive FORTRAN programming course and helped with writing subroutines for analysing bubble chamber photos. I had mastered a card punch machine and learned how to get their mighty CDC machine to accept and run a box of cards.

I was astonished to find that as a Diploma student in Cambridge, I was not expected to write programs in a high-level language like FORTRAN (only the PDP-7 team even acknowledged its existence, as far as I remember), and I had to write part of my dissertation on PDP assembler code and part in Titan machine code. The whole business of preparing and editing paper tapes seemed so ludicrously cumbersome compared with cards. If one was winding up a long tape without due care and it got caught round a table leg or tangled and tore, what a slow chore it was to position the two halves on a special block with pins and splice it with one of those little patches, using a hand punch to make the holes required in the area of the patch!

I came to appreciate the benefits of paper tape much less bulky to carry around and no danger of dropping a deck and getting cards out of order. I was introduced to the challenge and the fun of machine code programming and remember the tense atmosphere in the diploma students' room when the deadline for handing in dissertations approached. One of our year, Steve Bourne, wrote a text editor which paved the way for quicker and easier correcting of programs.

Karen Sparck-Jones (User1964 Reader now)

The Diploma students also had their own room in the old Lab building and indeed in the new building until IBM mainframes took all the space over. The students' room was on the top floor and was furnished with old barrack room tables; it was also used for the annual Christmas party, when the Lab was small enough to include everyone in a get together, with competitive games like making the most dashing newspaper hat (ladies for gentlemen).

At that time Catling's Auction Room was in Corn Exchange Street opposite the Lab, and lots of people used to pop down on viewing day: Lab research students setting up home could buy carved Victorian chairs for five shillings.

Guy and Annette Haworth (Diploma students 1968-69)

We did the Diploma course in 1968-69. I guess our claim to fame is that, although we had both been at Oxford on the same course before, we had never spoken. We met on the steps of Corn Exchange Street going into register for the Diploma and got married (a bit afterwards, of course) in Caius College. I'd like to claim that the meeting on the steps was truly romantic, but I don't think it was being immediately followed by a meeting in David Hartley's office registering for John Larmouth's FORTRAN course. We're still in computing-(ish).



Titan construction

Roy Bayley (Computer Engineer 1962-73)

When Titan arrived, it was bright and shiny and was installed in a bright and shiny air-conditioned room. You even had to walk over sticky mats to remove grit from your shoes before approaching the Holy Grail! However, EDSAC 2 operated a service, Titan did not. Titan was delivered to the Maths Lab by Ferranti/ICT straight off the production line. It had many faulty components and wiring errors. In fact many basic instructions did not work.

With Titan came two company engineers, Johnny and Gareth, whose task was to progress the Maths Lab team up the learning curve. Any readers around the Lab at this time will remember their well-deserved reputation for sinking large quantities of beer. Indeed, Sid Barton and I were amazed how they could return from a liquid lunch at the Eagle, having had the odd pint or five, stand swaying gently in front of the Engineers Console and still give sound advice on fixing faults. Faults that Sid and I were struggling to understand when sober!

Titan was a large asynchronous computer, consisting of 6 racks, with approximately 300 boards per rack. It had thousands of germanium transistors, tens of thousands of diodes and other discrete components. Each board carried only a small amount of logic, so fault finding by changing boards was of limited use. To fix faults the engineers needed to understand the voluminous computer logic and be able to adapt the test software to diagnose problems. It was a good learning experience. I enjoyed this time, working with a compatible team on a large mainframe computer, fixing different problems each day. Not so much a job, but a way of life. If only the pesky users would stop wanting to use the machine!

Initially the Titan system had several magnetic-tape drives, paper-tape readers, 64Kwords of RAM housed in units the size of a double wardrobe, but no printer.

In line with the Maths Lab 'Do It Yourself' ethos of the time, I was given the task of designing a printer for the Computing Service. Not something to be contemplated nowadays. The printer electronics were entirely designed and built in the Electronics Workshop. The mechanical part of the project was designed and built by Vic Claydon and his men in the Mechanical Workshop. Working with Vic was easy, as he didn't need detailed drawings. Just a few sketches, a bit of interaction and he would produce an excellent result.

The printer design used a basic ICT665 printer mechanism and the final product could print 120 characters per line at 600 lines/min (max) or 400-lines/min average. The printer had a ferrite core character buffer and the character set included upper and lower case characters, which was a real plus at the time.

The printer gave good service for some years, the characteristic ripping sound of its print hammers being part of the general noise of the Titan Computing Service in full flight.

Oliver Wintringham (Decca Radar)

In the sixties (1965?), I came for a job interview that might have led to my working on Titan, but (in those days of plentiful job offers) I eventually went elsewhere.

Richard Jennings (Diploma student 1962-63, Ferranti)

I took the Diploma course at the Laboratory in 1962-63, and then joined Ferranti/ICT and worked on the joint Cambridge/ICT project to develop the Titan Supervisor from 1963-65. My colleagues at that time included David Hartley, David Barron and Peter Swinnerton-Dyer.

Brian Chapman (ICL)

I was responsible for the installation of Fortran on Titan in early 1966. The Fortran compiler was designed by (and implemented by a small team led by) Alec Glennie of AWRE Aldermaston for their Atlas 2. This compiler was developed from one written earlier for their IBM 7030 'Stretch' computer.

The compiler was embedded within Hartran, a Fortran environment designed at AERE Harwell for their Atlas under the direction of Dr. Ian Pyle. Hartran provided a symbolic loader capable of combining Fortran (and potentially other) subroutines that had been separately compiled, and was the only such system program available on any of the Atlas family. Separate compilation was of course a natural extension of the earlier pioneering work at Cambridge with subroutines, and vital for any large program.

I personally had migrated the Hartran system from Atlas to Atlas 2, having earlier written the code generation phase of the first Atlas Fortran compiler at Harwell.

Peter Toye (Archimedean 1963-66, Diploma Student 1966-67)

Being told, when a program had stopped working "Oh, we changed that instruction last week, didn't you see the notice?"

Peter Hammersley (Senior Technical Officer 1966-69)

One day in 1967 (I think - but it may have been 1968) I was working with Neil Wiseman on the linking to an Atlas 2 (i.e. Titan) of terminals via modems. At the time we were in touch with Eric Thomas, who had been a research student at the Laboratory, and had moved to the Atlas Laboratory at Chilton to work on the front ending of terminals to the Atlas 1 via a Sigma 1 machine. We concluded that, between the three of us, if we each set up on Atlas a simulator of a terminal we ought to be able to make the two Atlases communicate computer to computer. This we did, realised how clever we were, and thought no more about it than the satisfaction of having done it. With hindsight weren't we stupid?

Richard Pankhurst (Research Assistant 1966-71)

I remember the rebuilding of the Lion Yard site, the ball swinging on the end of chain, the incessant pile driving.

When the New Museums site was first built sarcastic spirits used to say that the open area on the podium was daft cold and draughty (it still is), and would surely soon be filled with temporary hutments (seems not to have happened).


Titan maintenance


Richard Pankhurst (Research Assistant 1966-71)

In Titan days, when the machine had been down for repairs, there was a buzzer code which meant "operators come running, it's back again," which had us all running to our teletypes to log in again as fast as possible, to get the first in the processing queue. What was the code?


Titan operating

Judy Thomas, formerly Bowers (Operator 1961-67)

With the demise of EDSAC 2, Titan was commissioned in an air-conditioned room - bliss in the heat of summer. It was run 24 hours a day by teams of operators (many more of us now and nearly all called Sue), and a permanent night shift. Several programs ran in the computer at the same time, and if one went wrong, this could be a problem to all. One program generated only blank paper tape and could not be stopped until almost a whole reel had been used!

Philip Shaw (Operator 1967-69, Computer Science Tripos 1972-73)

Whilst I was at the Grammar School in Cambridge a friend got a guided tour around Titan courtesy of a member of the Laboratory staff who knew my maths teacher. It all sounded exciting, so I asked for a tour as well. At the end of the guided tour I had the cheek to ask for a job and subsequently became a part-time operator on Titan on Friday nights and some school holidays. I really enjoyed the job and, without going into details, my appearance for the Computer Science Tripos, meeting my wife, my career in computing, all stem directly from the small kindness of giving a guided tour to a schoolboy!

Karen Sparck-Jones (User1964 Reader now)

As most users were not allowed near the Titan (shut away in its own shiny room) we submitted our jobs by putting paper tapes in plastic bags along with colour-coded tickets e.g. pink for large jobs (30 minutes estimated time, or needing 3 magnetic tapes). These bags were hung on hooks on a board outside the Titan Room.

There was a cabinet with copies of library routine tapes (on green paper) e.g. RR10 - read integer, or PR10 - print integer, for copying into one's own program tapes.

The real gadget was the unipunch - that neat little hand punch that you could use to add holes to soup up one of your tape characters. Of course if there was too much hole already, you had to patch the tape like a bicycle tube to get a smooth stretch to punch anew.


Titan applications

Roger Stratford (User 1963-71, Computer Officer 1971-)

Schaefer's moved on to using the Titan and then I think our liaison person was Janet Richards (later Linington). Schaefer paid some nominal fee for the work! Schaefer Dielectrics had a research contract with RRE Malvern to develop high quality microwave dielectric materials for the radar on the ill-fated supersonic TSR2 aircraft.

About three years later, while working for the Cambridge Instrument Company, I again used the Titan. We were developing and running a Fortran program generating simulated microwave and infrared spectra. The Instrument Company was just getting into spectrometers at the time. I can recall working through the early hours of the morning because the response was so much better than during the day - and claiming overtime from the company, of course. The work eventually moved to the Atlas at the CAD Centre.

Then I joined the Computing Service at the end of 1971 and have been here ever since!


Titan people

Peter Hall (ICT/ICL)

As manager of the Ferranti Computer Department in the 1950s and 1960s, and later as a Director of ICT and ICL, I had a long standing association with Professor Wilkes. I was responsible for the company end of the collaboration that led to Titan.

Roy Bayley (Computer Engineer 1962-73)

It is sad that some members of the hardware dream team are no longer with us. It is a particular tragedy that Sid Barton was not part of the EDSAC 99 celebration. He played a valuable part on EDSAC, EDSAC 2 and Titan. He was a good engineer, dedicated to his work, with a rare common-sense approach to life and he had a good sense of humour. I worked with Sid for 12 years and towards the end of the 60s when Titan was up and running, we would tell the operators we were going to Millers Wine Bar for a little light refreshment! Now it can be told! We had many good chats together about computing, the possibility of Ice Ages (no global warming worries in the 60s), religion, the meaning of life, etc. We didn't come to any great conclusions but I still remember Sid and my days working on Titan with great pleasure.

Karen Sparck-Jones (User1964 Reader now)

During the work on Titan, and in it early operational life, Roger Needham, David Hartley, Barry Landy and Mike Guy shared a large office on the second floor of the old lab. It gradually accumulated piles and piles of ever dustier papers, manuals, etc. There was a lot of night work, and one morning when I went in to the office Mike Guy rose from behind the screen of paper piles, where he had been asleep stretched out on three chairs.

Judy Thomas, formerly Bowers (Operator 1961-67)

In 1965, I went out with one of the Diploma students who eventually became my husband, I think he had a very good turn round with his programs - somehow I seemed to find myself running them out of turn! We were married in September 1967 and left to live in Oxfordshire. I still look back on my time in Cambridge with affection.

Oliver Wintringham (Decca Radar)

In the seventies, I was one of the speakers at a seminar on Microcode, organised by the BCS, and chaired by Dr Wilkes. I was to give an introductory talk on Microcode and what it is useful for, and I naturally rang Maurice for advice. He very kindly referred me to an article in the IBM Systems Journal, which pleased and surprised me, since I was working for IBM at the time.

John Larmouth, (Diploma student 1962-63, - Computer Officer to 1978)

I was a student on the Diploma course around about 1963, and spent one year with the EDSAC 2. As a PhD student, I then produced the FORTRAN compiler for the Titan, and the scheduling system for the IBM System/370, and was on the staff for some twelve years up to around 1978.

Karen Sparck-Jones (User1964 Reader now)

Dedicated users from distant departments, or ones too lowly to rate significant office space in their departments, tended to roost permanently in the Lab, and after EDSAC 2's demise the console floor area was taken over as a users' pound, One of the adjoining offices was designated a Discussion Room, so people could be pushed in there to talk without disturbing the others in the pound. Later on these users earned a proper room on the ground floor, with lockers as well as tables. Nearby, in the Lab's informal style, there was an unlocked cupboard with a piece of Babbage's Analytical Engine (now firmly in the Whipple or some other proper museum), a wonderful machined brass object that Jack Dennis of MIT once demonstrated to me.

The old Lab building had large areas where ordinary people never went, like the third floor workshops, and stores with capacious shelving stacked with bins. Maybe all the engineers and assistants were naturally like that anyway, but the Lab's build it yourself style meant that all kinds of bits and pieces and redundant kit were kept in case they came in handy in some way. When we finally had to clear the old Lab there were always

people out scavenging souvenirs from the skips. (For some, the change in computing in the years since was poignantly marked by the reduction of the Lab workshops, especially the mechanical one.)

Richard Parkins (Assistant in Research 1969-72)

I later did a bit of vacation work for the Laboratory during  1967. This would have been my first paid employment. I think I was making some
improvements to Neil Wiseman's Scope Editor on the PDP-7. This was the machine on which I really cut my programming teeth, so to speak. From August 1969 until September 1972. I was doing research into Computer-Aided Design with Charles Lang's group. Apart from a brief interlude restoring antiques, I've been in some part or other of the Computer industry ever since.

Peter Toye (Archimedean 1963-66, Diploma Student 1966-67)

Marya Goldman, knee-high to a grasshopper, shouting "You stupid machine" to the PDP-7.



  1. M.V. Wilkes, Memoirs of a Computer Pioneer, MIT Press, 1985.
  2. IEEE Annals of the History of Computing, Special issue on the University of Cambridge, Vol. 14 (4), 1992.
  3. In the Beginning - Recollections of Software Pioneers by Robert L Glass, IEEE Computer Society, 1998
  4. Peter Naur, Impressions of the early days of programming, BIT 20 (1980) 414-425.


The editor is grateful to the following who submitted material for the compilation of reminiscences on the occasion of EDSAC 99. Given against each name are the relevant dates of association with the Laboratory and the position at that time.
Roy Bayley 1962-73 Computer Engineer 
Diana Belcham 1956-57 Diploma Student
John Bennett 1947-50 Research Student
David Brailsford - Nottingham University
Neil Breakwell 1948-49 Undergraduate 
Brian Chapman - ICL 
William Cochran 1946-64 User
Geoff Cook 1951-53 User/Research Student 
Durward Cruickshank 1950 Summer School
Edsger Dijkstra 1951 Summer School
Leonard Dresel 1949-52 User/Research Student
Philip Ekstrom 1963-64 Diploma Student 
Peter Fellgett 1962-65 User
George Felton 1946-51 Undergraduate
Harold Gearing - Metal Box Company
Peter Gray 1958-61 Undergraduate
Dick Grimsdale 1950 Summer School
Peter Hall - Ferranti/ICL
Peter Hammersley 1966-69 Senior Technical Officer
Jack Harwood 1949-50 User/Research Student 
Guy & Annette Howarth 1968-69 Diploma Students
Don Hunter 1949-51 Research Assistant
Richard Jennings 1962-63 Diploma Student, Ferranti
John Larmouth 1962-78 Diploma Computer Officer
John Lennard-Jones - Son of Maths Lab founder 
Jenifer Leech 1953-56 User/Research Student 
John Lindley 1958-59 Diploma Student
Charles Lindsey 1953-56 Research Student 
Ruth Loshak 1958-60 Programmer 
Herbert Norris 1951-63 Technician 
Richard Pankhurst 1966-71 Research Assistant 
Richard Parkins 1965-66
Assistant in Research
Stephen Parry 1966-67 Diploma Student 
Christopher Phelps Diploma Student
Mike Pitteway 1956-59 Research Student 
Colin Reeves 1952-55 User/Research Student 
Philip Shaw 1967-69 Operator 
D H Shinn 1947-50 User/Research Student 
Karen Sparck-Jones 1964- User - Reader
Robin Stokes 1948-49 User/Research Student 
Roger Stratford 1963-71 User 
Judy Thomas 1961-67 Operator 
Peter Toye 1966-67 Diploma Student
Elizabeth Waldram 1959-65 User 
Peter Wegner  1953-54 Diploma Student 
Donald Willis 1948-50, 1952-55 Research Assistant
Oliver Wintringham - Decca Radar 
Rachel Wroth 1965-66 Diploma student 


This is version 1.1 of the Reminiscences, reflecting its state on 21 July 1999.

Copyright University of Cambridge Computer Laboratory, 1999. All rights reserved.
Please send any comments to edsac99.