Work begins on hardware to aid Edsac replica recreation

Plans to rebuild the pioneering Edsac computer are a step closer to completion as parts that will form its metal chassis start to be manufactured.

Edsac - Electronic Delay Storage Automatic Calculator - ran its first program in 1949 and was created to help scientists at Cambridge University.

The rebuild project started in 2011 after it was found that few of the original design documents remained.

Project workers hope to have the recreated machine finished by 2015.

"In many ways, and people do not realise this, Edsac was the beginning of the computer age," said Hermann Hauser, who kicked off the whole project and made the first substantial donation towards the £250,000 needed to complete the rebuild. Cash has also come from Google and other anonymous donors.

Early work has focused on determining the parts and computational elements used in the 1949 Edsac. It was made up of more than 3,000 valves spread across a chassis made up of more than 100 steel shelves bolted to tall equipment racks.

Big thinking

With almost no original design documents remaining, rebuild volunteers have been forced to scrutinise photographs to puzzle out which bits go where, said Dr Andrew Herbert who is leading the recreation effort.

"We now understand what three-quarters of the chassis does," said Dr Herbert, "and the bits that are left are not central to the operation of the machine."

The recreation work had reached an important milestone, he said, as parts for the replica chassis started to be made. Close to Edsac's birthplace in Cambridge, Teversham Engineering has begun cutting, punching, sanding, bending and painting mild sheet steel into shelves that are the exact dimensions of those on the 1949 Edsac,

On to the shelves will be put the valves and other components that form the computational heart of the pioneering machine.

"It was the first computer that people could actually use," Mr Hauser told the BBC. "It was meant for ordinary scientists."

Most of the computers built prior to Edsac were purely experimental, said Mr Hauser. By contrast Prof Maurice Wilkes, who designed Edsac, began with the idea of making a machine that would be a workhorse for Cambridge scientists.

Science was being stunted at the time by the limitations of mechanical adding machines, said Mr Hauser.

"Edsac let scientists tackle problems that could never have been solved with mechanical calculators," he said. "It revolutionised the way a lot of Cambridge scientists thought about what they could do."

Its introduction represented the biggest step function improvement in computing power ever, said Mr Hauser. Rough estimates suggest it was about 1,500 times faster than the best mechanical hand-cranked calculator of that era, he added.

The rebuild of Edsac will be done in public at the National Museum of Computing at Bletchley Park.