Computer Conservation in the United Kingdom: The EDSAC Replica Project

Recreating a fully functioning EDSAC computer is quite a challenge, but our experience in rebuilding the Colossus computer gives us confidence and insight. - Kevin Murrell, Director and Trustee The National Museum of Computing

The Computer History Museum is very pleased to welcome Kevin Murrell to our stage for a lecture about computer conservation in the United Kingdom. Mr. Murrell will provide an overview of the British Computer Society’s Computer Conservation Society (CCS) and its restoration projects, including the EDSAC replica project, and the restoration of the Harwell Dekatron computer. The CCS has a twenty year track record in successfully recreating pioneering computers.

Mr. Murrell’s visit coincides with that of Dr. David Hartley, who will visit our stage later in the evening to pay tribute to Sir Maurice Wilkes and his many achievements, among them the design and creation of the EDSAC.

The Electronic Delay Storage Automatic Calculator (EDSAC) was a general purpose research tool at Cambridge University and also led directly to the first business computer. It is planned to recreate EDSAC in full public view at The National Museum of Computing at Bletchley Park. The project, which is expected to take three to
four years, is being funded by a consortium led by computing entrepreneur, Hermann Hauser.


EDSAC Facts
• EDSAC was based on the ideas of John von Neumann and others who in 1945 suggested that the future of computing lay in computers which could store sets of instructions (programs) as well as data.
• EDSAC was over two metres high and occupied a ground area of four metres by five metres.
• Its 3000+ vacuum tubes used as logic were arranged on 12 racks.
• Mercury-filled tubes acted as memory
• It performed 650 instructions per second.
• EDSAC ran its first program on 6 May 1949 and soon began nine years of regular service ending in July 1958 when it was dismantled to enable the re-use of precious space. By then it had been superseded by the faster,
more reliable and much larger EDSAC 2.



Professor Andrew Hopper, Head of the Computer Laboratory at Cambridge University, said: EDSAC set computing standards for academia and commerce. It was so successful that in the nine years following 1949 it was used by Cambridge University researchers in studies such as genetics, meteorology and X-ray crystallography and even helped two researchers win Nobel prizes. EDSAC also led directly to the first
commercially applied computer, the LEO, that broke new ground by enabling the catering company J Lyons & Co Ltd to perform payroll calculations in 1953.

The recreation will be as authentic as possible and true to the spirit and technology of the time. Occupying a floor area of 20 square metres, the replica EDSAC is planned to be a highly visible display. The original had over 3000 electronic tubes (or valves) used for logic, mercury-filled tubes for memory, data input via paper tape and output on a teleprinter. Only the mercury-filled tubes are expected not to be recreated – in compliance with modern safety requirements – and will be substituted with a similar delay line storage technology.