Oldest digital computer switched back on at Bletchley museum

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AN ancient computer renowned for its faultless calculations was re-booted today.

The Harwell Dekatron or WITCH became the world’s oldest original working digital computer when it was switched back on at The National Museum of Computing (TNMOC).

It followed a three year restoration project at the Bletchley Park based museum.

Now in its seventh decade and in its fifth home, the machine will provide an awe-inspiring display for visitors keen to learn about Britain’s rich computer heritage.

The 2.5 tonne, 1951 computer was re-booted in the presence of two of its original designers and one of its first users.

Trustee of TNMOC, Kevin Murrell, who initiated the restoration project, said: “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.

“As the world’s oldest original working digital computer, it provides a wonderful contrast to our rebuild of the wartime Colossus, the world’s first semi-programmable electronic computer.”

The computer first ran at Harwell Atomic Energy Research Establishment in 1951, where it automated the tedious calculations performed by talented young people using mechanical hand calculators.

Designed for reliability rather than speed, it could carry on relentlessly for days at a time delivering its error-free results. It wasn’t even binary, but worked in decimal.

By 1957, the computer had become redundant at Harwell, but a scientist at the atomic establishment arranged a competition to offer it to the educational establishment putting up the best case for its continued use.

Wolverhampton and Staffordshire Technical College won, renamed it the WITCH (Wolverhampton Instrument for Teaching Computation from Harwell), and used it in computer education until 1973.

After a period on display in the former Birmingham Museum of Science and Industry, it was dismantled and put into storage, but ‘rediscovered’ by a team of volunteers from TNMOC in 2008.

With the blessing of the Birmingham museum and in conjunction with the Computer Conservation Society, the team developed a plan to restore the machine.

Mr Murrell said: “I first encountered the Harwell Dekatron as a teenager in the 1970s when it was on display in the Birmingham Museum of Science and Industry – and I was captivated by it.

“When that museum closed, it disappeared from public view, but four years ago quite by chance I caught a glimpse of its control panel in a photograph of stored equipment. That sparked our ideas to rescue it and we hunted it down.

“The TNMOC restoration team has done a superb job to get it working again. To see it in action is to watch the inner workings of a computer, something that is impossible on the machines of today.”