Historical Computer Systems – The EDSAC

At the beginning of the computer age, there were various computer systems of differing construction and operational principles. Among these were the Z3, an electromechanical computer designed by the German civil engineer, Konrad Zuse, which incorporated data storage through the use of punched 35mm film, the electronic Atanasoff-Berry Computer designed by John Atanasoff, Howard Aiken’s Harvard Mark 1 and the famous ENIAC, designed by John Mauchly and J. Presper Eckert. While these machines varied in design and operation, they were all built with one specific task: to make the task of calculation quicker.

Before George Stibitz demonstrated the relay-based electromechanical Complex Number Calculator, the earliest electrical tabulator to exist, complex calculation was done using slow desk-mounted mechanical tabulators. With the simultaneous developments of Zuse, Atanasoff, Aiken and Britain’s Alan Turing, which came just in time to assist the war effort in the Second World War, the world had seen the nascent developments of a technology which would eventually revolutionise society. First, though, the computer had to become more than an elaborate calculator.

In the years following the Second World War, work by Turing, Eckert and Mauchly, along with John von Neumann, the Hungarian-born polymath, led to the development of the stored-program computer using what became known as the von Neumann architecture. The release of von Neumann’s paper, First Draft of a Report on the EDVAC, led to the development of a number of stored-program computers around the world. The first of these was the experimental SSEM, or Small-Scale Experimental Machine, a prototype computer developed in Manchester and designed to test the Williams tube, an early form of computer memory. This, in turn, influenced the development of the EDSAC at the University of Cambridge.

The EDSAC, or Electronic Delay Storage Automatic Calculator, was the first practical electronic stored-program computer. Completed in May 1949, the EDSAC took input from punched tape and printed output through a teleprinter, both methods which would find use long after the development of the EDSAC. Output could also be displayed on a series of CRT monitors, an interesting capacity which would play a role in a historic piece of software for the machine.

A picture of the room-filling EDSAC at the University of Cambridge.

In the years preceding and during the operation of the EDSAC, a number of computer scientists and mathematicians were devising applications for computers which would go beyond the military and academic mathematics tasks that the computers had been performing to that point. Alan Turing was conceiving of artificial intelligence, others were considering mathematics in fields such as chemistry and biology, and a few people had even considered experimental computer games. One of these was A. S. Douglas, a mathematician at Cambridge who, as part of his doctoral thesis on human-computer interactions, designed one of the first computer games.

OXO, or Noughts and Crosses, to give it its full title, was, as the name suggests, a simulation of tic-tac-toe designed to test the EDSAC’s capacity for doing things other than routine mathematics. Being a game with simple rules, the game wasn’t very sophisticated by today’s standards, but it worked – something notable when discussing a computer made less than a decade after the very first electronic computer.

The EDSAC design led to other applications as well. J. Lyons & Co. Ltd., a now-defunct restaurant, food manufacturing and hotel company in Britain, whose products included the popular Ready Brek cereal, had invested in the EDSAC project. From the EDSAC design came LEO I, one of the first commercial computers ever produced, and the first computer to be used for business applications. LEO I (standing for Lyons Electronic Office) efficiently ran through inventory and payroll jobs, first for J. Lyons & Co. themselves, then later for Ford UK. A LEO I computer was also used by the Met Office before the acquisition of their own computer in 1959.

The EDSAC as originally designed ran with a clock speed of 0.5MHz, and had 512 17-bit words in its mercury delay line memory. This was later expanded to 1024 words – just over 2kB of RAM, in modern parlance. All of this operated at approximately 700 operations per second, moderately quick but slightly compromised at the time, and beatable by even the least sophisticated modern microcontroller. Given that the EDSAC required 12kW of electrical power to operate, it demonstrates just how far we’ve come in the sixty-one years since the EDSAC ran its first application.

The EDSAC’s historical value is unquestionable for being the first practical von Neumann-compliant computer to be built. However, there are other reasons for the EDSAC to be historically interesting. The first are its applications outside of pure and applied mathematics, such as the derived LEO I’s business applications and OXO. The second is the existence of a fully-featured simulator for the EDSAC, made in 1996 by the computer scientist and historian, Martin Campbell-Kelly. While it doesn’t give the experience of a heated room full of vacuum tubes and paper tape readers, it’s still an interesting insight into the programming techniques of a first-generation computer.

Reports from the start of the year also suggest that a replica of the EDSAC is to be built at Bletchley Park (home of the Colossus code-breaking computers during the Second World War). As there are few components remaining from computers of the first generation, and only a single complete one in existence – Australia’s CSIRAC, also known as the first computer to play digital music – this will prove to be one of the few chances to see a computer with first-generation technology in action. (EDIT 10/09/2013: As pointed out in the comments by Robert Dowell, the WITCH, a British computer also from the first generation, was painstakingly restored to working condition by The National History of Computing at Bletchley Park, and was made operational in 2012.)

The EDSAC was later superseded by the EDSAC 2, another vacuum tube computer which served until the mid-1960s. During its time, it was responsible for accelerating several mathematical fields, as well as forming a bedrock for the British computer industry. LEO Computers Ltd., formed to sell LEO business computers, eventually amalgamated with English Electric, which led to the formation of ICL, one of Britain’s historically most successful computer manufacturers. The von Neumann architecture underpinning the EDSAC would go on to underpin almost every computer which followed.


2 Responses

  1. Even though the Australian CSIRAC is indeed the earliest complete 1st generation machine, it is by no means the only one. The other problem with the CSIRAC, is unfortunately they do not believe that it will ever be operational again. The WITCH computer is an actual working 1st generation machine that is currently housed at The National Museum of Computing at Bletchley Park. Operational as of 1951, it has just entered the Guinness Book of Records as the oldest original working digital stored programme computer on the planet. Not bad for a 62 year old machine.

  2. I was aware of the WITCH, having followed the project somewhat for a while before they got the computer back into operation. I was rather pleased when they got the WITCH back into operation, because it’s a real connection with the computers of the past which one can actually observe.

    If I recall correctly, the dekatron memory in the WITCH has a neat effect rather like blinkenlights in other computers, where you can visibly see effects on the memory as the computer operates. As much as blinkenlights may have been originally designed as a way of impressing people outside of the field of computing, there is a certain charm to them which I will always associate with early computing.

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