Computer enthusiasts give Witch a new lease of life at Bletchley

20 Nov 2012


Computer enthusiasts at The National Museum of Computing, home of the rebuilt Colossus electronic computer have completed another remarkable restoration project, rebooting the Harwell Dekatron – otherwise known as the Witch – making it the world's oldest original working computer.

The team at the museum, led Kevin Murrell has spent three years restoring the Harwell Dekatron, having first come across the machine as a teenager.

“In 1951 the Harwell Dekatron was one of perhaps a dozen computers in the world, and since then it has led a charmed life surviving intact while its contemporaries were recycled or destroyed,” said Murrell.

The Harwell Dekatron was originally used in 1951 to check atomic calculations, and while it could take up to 10 minutes to multiply two numbers together, it could chug away for days on end, producing error-free results.

Weighing in at 2.5 tonne, sporting 828 flashing Dekatron valves, 480 relays and a bank of paper tape readers, the 2x6x1m Harwell Dekatron is world away from today's supercomputers – or even the smartphones and tablets we carry.

“To see it in action is to watch the inner workings of a computer - something that is impossible on the machines of today,” said Murrell.

By 1957, the Harwell Atomic Energy Research Establishment had no more need for its Dekatron computer, and gave it to the Wolverhampton and Staffordshire Technical College  - where it was renamed the Witch (Wolverhampton Instrument for Teaching Computation from Harwell).

The National Museum of Computing, located at Bletchley Park, is home to the largest collection of functional historic computers in Europe, including a rebuilt Colossus, the world’s first electronic semi-programmable computer.

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