One of the oldest digital computers is a step closer to running again — albeit in replica form. Bletchley Park researchers have demonstrated working parts in the replica, marking the midway point of the project.

The Electronic Delay Storage Automatic Calculator, built at Cambridge University, was among the early machines to meet three key criteria — electronic, digital and capable of being reprogrammed — that made it effectively what we think of as a computer today rather than an abacus or calculator.

Strictly speaking two machines from Manchester met this criteria and predated EDSAC. However, the first was more for demonstration purposes than practical use. The second, the Manchester Mark 1, was made available for use a month before EDSAC, though was still in development and wasn’t completed until later.

Staff at a computing museum in Bletchley Park (home of the British efforts to crack German encryption during the second world war) began work on a replica in 2011 with the aim of finishing in 2015.

The BBC notes its been a particularly challenging project as staff have few of the original design documents. Instead they’ve had to piece together the components, including 3,000 valves on 140 shelves, from surviving photographs of the original.

Staff had got some replica parts working and showed them off to commemorate the 100th anniversary of the birth of Maurice Wilks, who led the work on creating the original EDSAC.

Although most of the machine will be made with replica parts, some components will be more authentic. One person working on the project, Bill Purvis, recently details how he worked on a genuine teleprinter, using a motor from a local electronics store and then testing the device by connecting it to a Raspberry Pi.

(Image credit: Computer Laboratory, University of Cambridge, via Creative Commons licence.)