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When volunteers began rebuilding one of the world’s first fully rnoperational general-purpose computers they had to painstakingly piece rntogether the inner workings of the 65-year-old machine.

The original EDSAC – the Electronic Delay Storage Automatic Calculator – rnwas built immediately after World War II at the University of Cambridge,rn where it aided research into areas including genetics, meteorology and rnX-ray crystallography. The machine’s design was later used to create rnLEO, the world’s first business computer.

With the historic EDSAC scrapped decades ago, the 20 volunteers recreating the computer had torn scrape together information about the machine. For guidance the team rnconsulted documents held by individuals and in libraries at the University of Cambridge, and examined the one surviving chassis used in the EDSAC.

Nowrn the team working out of Bletchley Park in England, home to the famous rnWorld War II codebreakers that included father of computing Alan Turing,rn have had confirmation the rebuild is on the right track after stumblingrn across diagrams of the original machine.

The 19 detailed rncircuit diagrams, which came to light more than 60 years after they werern drawn up, were delivered to the team by chance.

For decades rnthe drawings sat in the home of John Loker, who worked as an engineer inrn the maths lab at the University of Cambridge and came across the rndiagrams in 1959, just after EDSAC had been decommissioned.

“In a rncorridor there was a lot of stuff piled up ready to be thrown away, but rnamongst it I spotted a roll of circuit diagrams for EDSAC. I’m a rncollector, so I couldn’t resist the urge to rescue them,” he said.

“Itrn wasn’t until I visited TNMOC [The National Museum of Computing at rnBletchley Park] recently and learned about the EDSAC Project that I rnremembered I had the diagrams at home, so I retrieved them and gave themrn to the project.”

Many of the diagrams, which date from between rn1949 and 1953, were drawn after EDSAC had been constructed and are rnthought to have been an aid in refining the original machine and in rndesigning its successor. They are believed to have been part of a much rnlarger set of at least 150 drawings and are in remarkably good rncondition.

Andrew Herbert, leader of the EDSAC Project rebuild, rnsaid: “Thankfully, the documents confirm that the reconstruction we are rnbuilding is basically correct, but they are giving us some fascinating rninsights about how EDSAC was built and show that we are very much in rntune with the original engineers: both teams have been exercised by the rnsame concerns.

“Importantly, the drawings clearly show that the rnaim of EDSAC’s designer, Sir Maurice Wilkes, was to produce a working rnmachine quickly rather than to create a more refined machine that would rntake longer to build. The refinements could come later — and many did rnas the sequence of diagrams over the five-year period shows.”

Above, from left, is EDSAC technical leader Chris Burton, with John Loker, the engineer who saved the diagrams, and leader of the EDSAC Project rebuild Andrew Herbert.