Discovery of rare part of early computer

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EDSAC reconstruction team eager to find out if there could be more

A very rare original part of EDSAC, one of the world’s first computers, has resurfaced in the USA and the discovery suggests that other parts of EDSAC may still be in existence.

The part, a chassis (1A) designed to hold 28 of the 3000 EDSAC valves, has just been donated to the EDSAC team at The National Museum of Computing (TNMOC), where the ongoing reconstruction of EDSAC, originally built in Cambridge in the late 1940s, is on display. The reconstruction is expected to be completed later this year and is already a very popular exhibit especially amongst the many educational groups that visit the Museum.

The EDSAC Chassis part is said to have been acquired at some sort of auction of EDSAC parts in Cambridge in the 1950s when the computer was decommissioned.

Andrew Herbert, leader of the EDSAC reconstruction project at TNMOC, said: “Details of the ‘auction’ are unclear, but there is a possibility that other parts of the original EDSAC still exist and could even be in the Cambridge area stored away in lofts, garden sheds and garages. We would very much like to hear from anyone who thinks they may have other parts.”

The Chassis 1A has been donated by Robert Little, from Allentown, Pennsylvania, USA, after he read about the EDSAC reconstruction project at TNMOC. He had obtained the part in 1969 from Dr Robert E Clark, who at that time lived in Collier Road, Cambridge. Earlier Dr Clark had bought three or four EDSAC racks with the intention of converting them into bookshelves. The other chassis were later discarded, although some may have been given to colleagues.

Robert Little said: "I regret that the probability of finding any more of Dr Clark's EDSAC parts is vanishingly small. Dr Clark passed away in 1984. Sometime between 1969 and 1984 he relocated to a house on the outskirts of Cambridge and quite probably disposed of unneeded things then.

"The bulk of the machine was most likely destroyed. I have a vague recollection of Dr Clark describing how he was bidding against the local scrap metal dealer when he won the EDSAC parts at auction. Despite this, I am hopeful that those who built and worked with EDSAC kept other mementos that have been preserved intact until now."

Andrew Herbert continued: "Chassis 1A is quite distressed with corrosion and much of the wiring has broken away from tag strips. It would be a major task to return this particular chassis to operating condition. However, we hope to try to use some of the valves, if they are still functional, in our reconstructed EDSAC thus providing a very tangible connection with the original machine.

"We would very much like to know if more of these chassis have survived. We think that as many as 42 of this type existed in the original machine. When EDSAC was decommissioned, only three chassis were thought to be in existence – one in the Cambridge University Computer Laboratory (since loaned to The National Museum of Computing), one in the London Science Museum and one in the Computer History Museum in Silicon Valley. This is the first time any of our Project Team has heard of the auction and it's tantalising to think that more parts of the original EDSAC might be out there – somewhere! It is also exciting to think that we may have stumbled across the first computer auction!"

The chassis were a vital component of EDSAC. Built in modular fashion, EDSAC had 12 vertical racks which could hold up to 14 individual horizontal chassis. Each chassis provided all or part of one of EDSAC’s logically distinct functional units. There were about 70 different types of chassis. Some were represented only once while others were replicated. Chassis type 1A is a Storage Regeneration Unit that keeps data recirculating through a short or long tank. There were 42 identical Store Regeneration Units.

The chassis variants look quite similar: they all have two long rows of 14 holes each, for valve-holders, allowing each chassis to hold up to 28 valves. Given that it takes three pentode and two diode valves to build an "AND" gate, each EDSAC chassis is therefore barely equivalent to even the simplest of modern integrated circuits.

Chassis 1A is the latest surprising original find for the EDSAC Project Team. Last year, some early EDSAC diagrams resurfaced after decades in storage.

The EDSAC display, recently opened at The National Museum of Computing, enables visitors to see progress of the ongoing reconstruction of one of the most influential early computers.

Top quality videos of the EDSAC project as it progresses are on YouTube.

Here is the general overview video at the start of the project:

Notes To Editors


EDSAC, the Electronic Delay Storage Automatic Calculator, was built immediately after World War II by a team led by Sir Maurice Wilkes in the Mathematical Laboratory of the University of Cambridge. It was one of the first practical general purpose computers and was used by scientific researchers across the University. The EDSAC design was later developed to create LEO, the world's first business computer.

  • 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 in a memory.
  • EDSAC was over two metres high and occupied a ground area of four metres by five metres.
  • Pre-dating the transistor, its 3000+ thermionic valves / vacuum tubes used as logic were arranged on 12 racks containing just over 140 chassis in total.
  • Mercury-filled tubes were used for the main memory, comprising 512 words initially, later 1024 word (equivalent to 2KB/4KB of PC storage).
  • It performed 650 instructions per second, effectively computing more than 1500 times faster than the mechanical calculators it replaced.
  • EDSAC read in programs from paper tape and printed its results on a teleprinter.
  • EDSAC ran its first program on 6 May 1949 and soon after that began nine years of regular service for scientific users across the University of Cambridge and other institutions, 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 and much larger EDSAC 2.

2 The EDSAC Reconstruction Project

The EDSAC Reconstruction Project which began in 2011 is expected to be completed in late 2015. The reconstructed EDSAC, which will occupy 20 square metres, is being built at The National Museum of Computing, where visitors can see the work in progress. The EDSAC Replica Project has been funded by a consortium led by Hermann Hauser.

The ongoing reconstruction story featuring videos of progress can be seen at

3 About The National Museum of Computing

The National Museum of Computing, located on Bletchley Park, is an independent charity housing the world's largest collection of functional historic computers, including the rebuilt Colossus, the world’s first electronic computer, and the WITCH, the world's oldest working digital computer. The Museum enables visitors to follow the development of computing from the ultra-secret pioneering efforts of the 1940s through the large systems and mainframes of the 1950s, 60s and 70s, and the rise of personal computing in the 1980s and beyond.

A pledge by an individual benefactor of £1 million if matched funding is found means that every pound or dollar donated to the Museum will count double. Previous funders of the Museum have included Bletchley Park Capital Partners, Bloomberg, CreateOnline, Ceravision,, Ocado Technology, FUZE, 4Links, Google UK, IBM, NPL, HP Labs, and BCS.

The whole Museum is currently open to the public on Thursdays, Saturdays and Sundays from 12 noon, spring and summer Bank Holidays and increasingly during school holidays. Colossus and Tunny galleries are open almost every day. Guided tours are available at 2pm on Tuesdays. There are often additional opening times for the public -- see the website or the iPhone app for updates. Educational and corporate groups are very welcome and may be on any day or evening by prior arrangement.

For more information, see and follow @tnmoc on Twitter and The National Museum of Computing on Facebook and Google+. A TNMOC iPhone App is also now available from the iPhone App Store.

Media Contacts
Stephen Fleming for the EDSAC Project at The National Museum of Computing
01635 299116

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