Oldest digital computer rebooted at The National Museum of Computing in Bletchley

By Culture24 Reporter | 21 November 2012
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A photo of a huge and extremely complicated old computer with hundreds of valves
The Harwell Dekatron is back on public display© Robert Dowell, The National Museum of Computing
A three-year restoration of a relic at The National Museum of Computing is complete. Having been rebooted, the Harwell Dekatron – a 2.5-tonne, 1951 design with 828 flashing valves, 480 relays and a bank of paper tape readers – is back in action as the world’s oldest original working digital computer.

“I first encountered the Dekatron as a teenager during the 1970s,” says the Bletchley venue’s Kevin Murrell, describing a machine better known as the WITCH.

“It was on display at 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.”

A photo of dozens of glowing red lights in a row on an ancient computer
The WITCH nickname comes from its former title as the Wolverhampton Instrument for Teaching Computation from Harwell© The National Museum of Computing
This is the Dekatron’s fifth home, and school groups seem enamoured by its clattering mechanism.

“It is already proving to be a fascination to young and old alike,” reports Murrell. “The 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.

“The restoration has been in full public view and even before it was working again the interest from the public was enormous."

This is the Dekatron’s fifth home, having originally whirred at the Harwell Atomic Energy Research Establishment, where it automated “tedious” calculations performed by human prodigies on mechanical hand calculators.

Working in decimal and noted for its inexhaustible reliability rather than speed, it eventually became redundant.

Wolverhampton and Staffordshire Technical College won it after putting forward the most convincing plans for its future, and it remained an education tool until heading to Birmingham in 1973.

"In 1951, the Dekatron was one of perhaps a dozen computers in the world,” summarises Murrell.

“Since then it has led a charmed life, surviving intact while its contemporaries were recycled or destroyed.”

A photo of a male technician in a grey t-shirt with a headtorch looking at a computer
Volunteer Delwyn Holroyd takes a look at the machine declared the world's most durable computer in 1973© The National Museum of Computing
He says it offers a “wonderful contrast” to the rebuild of the pioneering semi-programmable wartime Colossus computer, carried out by the museum’s experts.

“The restoration of the Dekatron was quite a challenge,” admits one of them, volunteer Delwyn Holroyd.

“It required work with components like valves, relays and paper tape readers that are rarely seen these days and are certainly not found in modern computers.

“Older members of the team had to brush up on old skills. Younger members had to learn from scratch.”

For once, perhaps, the oldest computer is the best.
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