EDSAC History

The Electronic Delay Storage Automatic Calculator (EDSAC) was originally built in in the Cambridge University Mathematical Laboratory by a team lead by the late Professor Sir Maurice Wilkes immediately following the Second World War.

It is generally accepted that the EDSAC was the first practical general purpose stored program electronic computer. Other, earlier machines were either dedicated to a single task (e.g. Colossus and code breaking) or were purely experimental (e.g. the Manchester University "Baby" Small Scale Experimental Machine).

As head of the Mathematical Laboratory, Wilkes’ brief was to provide 'mechanical' aids that would assist mathematicians, scientists and engineers at the university to perform complex and time-consuming calculations. He had observed research workers doing laborious computations with the aid of mechanical desk calculators and mathematical tables. His prime motive in building EDSAC was to provide them with faster and better facilities.

Wilkes’ vision was to create a computer which, unlike earlier machines, could be used by a wide range of researchers in the university instead of the few highly specialised ‘acolytes’ who tended the other early electronic computers. He wanted to create a computer that was accessible and practical, rather than to push the boundaries of technology. To reach that goal, he adopted very conservative design principles and the result was a reliable machine that did useful and significant work through its life. It typically operated for 35 hours a week. During the day there were engineers on hand to deal with problems that arose. Approved users could work on the computer overnight, but if it broke down they had to wait until morning before it would be investigated.

Like all computers of its time, EDSAC was based on thermionic valves which Wilkes knew well from his wartime work on advanced radar systems. He sketched out the main elements of the design during a five day voyage from the USA to the UK while returning from a seminal conference of American computing pioneers at Princeton University.

Construction was led by Bill Renwick, appointed by Wilkes as Chief Engineer. A team quickly grew around Wilkes and Renwick as they refined the design and gradually brought EDSAC to life. Another important contributor at this stage was David Wheeler, Wilkes' research student, who was responsible for many of the features that made the machine practical for ordinary users.

EDSAC ran its first program on 6th May 1949 and was soon pressed into service to support research in the university. It provided a computing service for over nine years, until it was superseded by EDSAC 2, built by the same team.

During that period a substantial number of users had their research transformed and their horizons extended through the increase in computer power that EDSAC and EDSAC 2 gave them. Among these were future winners of three Nobel Prizes - John Kendrew and Max Perutz (Chemistry, 1962) for the discovery of the structure of myoglobin, Andrew Huxley (Medicine, 1963) for quantitative analysis of excitation and conduction in nerves and Martin Ryle (Physics, 1974) for the development of aperture synthesis in radio astronomy. All acknowledged EDSAC in their Nobel Prize speeches.

EDSAC and its many uses won recognition and financial support from outside sources. In particular funds were provided by the catering company J Lyons, which went on to build the LEO I computer, the world's first business computer, based on the EDSAC design,

EDSAC was modest in terms of modern-day computers. There were only 18 operation codes and initially just 512 words of memory, later extended to 1024. Instructions were executed at a rate of approximately 650 per second. Input was by punched paper-tape and output by teleprinter.

Although today’s PCs operate can perform calculations millions of times faster than EDSAC, EDSAC was a huge improvement on what was available at the time - human calculators using mechanical desk machines. It has been estimated that EDSAC introduced a 1,500 times productivity increase, and transformed the progress of research throughout Cambridge University. Researchers became able to solve problems that were previously considered either impractical or impossible.

EDSAC 1951 Film

Maurice Wilkes' 1976 commentary on the 1951 film about how EDSAC was used in practice: