Oldest digital computer re-booted at Museum of Computing

Dickie Barnes, one of the Harwell Dekatron's original designers, at the re-boot of the computer at The National Museum of Computing
Dickie Barnes, one of the Harwell Dekatron's original designers, at the re-boot of the computer at The National Museum of Computing

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 – with its flashing lights and clattering printers and readers – will provide an awe-inspiring display for visitors keen to learn about Britain’s rich computer heritage.

The 2.5 tonne, 1951 computer from Harwell with its 828 flashing Dekatron valves, 480 relays and bank of paper tape readers, 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 – a feature that is displayed by its flashing Dekatron valves.

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 and it is already proving to be a fascination to young and old alike. 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.”

Delwyn Holroyd, a TNMOC volunteer who led the restoration team, said: “The restoration was quite a challenge requiring 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 while younger members had to learn from scratch.”

The computer can be seen whenever The National Museum of Computing is open.

WITCH fact file:

1949 Design begun

1951 First operated

1957 Moved to Wolverhampton

1973 Declared world’s most durable computer

1973 Moved to Birmingham Museum of Science and Industry

1997 Moved into storage at Birmingham Collections Centre

2009 Moved to TNMOC

2012 Re-booted to become the world’s oldest original working digital computer

Power Consumption: 1.5kW

Size: 2m high x 6m wide x 1m deep

Weight: 2.5 tonnes

Number of Dekaton counter tubes: 828

Number of other valves: 131

Number of relays: 480

Number of contacts or relay switches: 7,073

Number of high speed relays: 26

Number of lamps: 199

Number of switches: 18