EDSAC to be Rebuilt

The BBC News site has a report on a project to rebuild EDSAC, one of the world’s first working computers.

The first recognisably modern computer is to be rebuilt at the UK’s former code-cracking centre Bletchley Park.

The Electronic Delay Storage Automatic Calculator (EDSAC) was a room-sized behemoth built at Cambridge university that first ran in 1949.

The project, commissioned by the the Computer Conservation Society of the UK, will be carried out at Bletchley Park, home during World War II of the Government Code and Cipher School, also called Station X, which was the center of British code-breaking efforts against the Axis powers.  It was the site of the successful operation, led by Alan Turing, to intercept and decrypt the German Enigma messages.

The EDSAC was noteworthy because, unlike some roughly contemporary machines, it had its program stored in memory, rather than having it determined by patch cables and switches, as in ENIAC.   (The University of Cambridge Computer Laboratory has an information page on EDSAC.)  Its memory consisted of 1024 17-bit words, implemented with mercury delay-line technology.  (The rebuilt version will use a substance other than mercury, for safety reasons.)  It used 3,000 valves (vacuum tubes), consumed 12 kW of power, and occupied a 5 x 4 meter room.  It could read input from paper tape at 6.6 characters per second, and executed instructions at the blistering rate of 650 per second.  Though this seems laughably primitive by today’s standards, the machine was a real advance in computing, and was used productively for nine years.

The project is expected to cost £ 250,000, paid for by a fund-raising consortium led by Herrman Hauser, and is expected to take three years.  Visitors to the UK National Museum of Computing, also located at Bletchley Park, will be able to see the work in progress.

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