A computer conservation project to build a working replica of one of the first general purpose computers has reached an important milestone. Work has now begun on manufacturing the huge steel chassis required to replicate EDSAC as it was in 1949.

Originally announced two years ago, the project to rebuild the Electronic Delay Storage Automatic Calculator is on schedule for completion in 2015.

EDSAC I, W.Renwick, M.Wilkes. Copyright Computer Laboratory, University of Cambridge. Reproduced by permission. (Click to enlarge).

EDSAC project manager, Andrew Herbert, explained the decision to undertake this challenging exercise:

"EDSAC marks a hugely important early milestone in computing. Until EDSAC, general purpose computers had been purely experimental systems locked away in research laboratories. But the late Professor Sir Maurice Wilkes, now widely regarded as the father of British computing, had the vision and the drive to realize the potential of computers to take on the mathematical calculations that underpin scientific research. He led the team that built the original EDSAC for the Mathematical Laboratory at Cambridge University. The impact of that new facility contributed quickly and directly to Nobel prize-winning scientific research, and to LEO, the first computer used in business. The impact of EDSAC has been profound, so we aim to celebrate the achievements of its creators and to inspire future generations of engineers and computer scientists."

As this video explains the main challenge facing the team of volunteers who are working on the rebuild is the lack of documentation. There are almost no original design documents remaining so the rebuild volunteers have to scrutinize photographs to puzzle out which bits go where.

There are also few original components since when EDSAC was scrapped in the late 1950s only three of its 140 chassis survived.  It is one of these that is being  as the model for the production of the first 20 replica chassis at Teversham Engineering Ltd in Cambridge.

Manufacturing the chassis with modern technology at Teversham Engineering, Cambridge.

EDSAC relied on mercury delay lines for storage, but as  mercury delay lines required frequent replacement and mercury is a poison, nickel delay lines, which were almost contemporary, will be used in the reconstruction instead.

One of the three surviving chassis for the original EDSAC.

An original chassis together with an original mercury delay line will soon be included in the display of  EDSAC artifacts at The National Museum of Computing (TNMOC) where the EDSAC recreation is taking place.