The Witch makes a comeback at The National Museum of Computing

Oldest working digital computer goes on display

The WITCH is back! After a three-year restoration project at The National Museum of Computing, the Harwell Dekatron computer has gone on show today as the world’s oldest original working digital computer.

Also known as the WITCH, the computer is now in its seventh decade and fifth home. Originally put together in 1951, the computer weights approximately 2.5 tonnes and features 828 flashing Dekatron valves, 480 relays and a bank of paper tape readers.

With its flashing lights and clattering printers and readers, it’s expected to provide an inspiring display for visiting school groups and the general public keen to learn about the museum’s rich computer heritage.

Kevin Murrell, trustee of TNMOC 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 Harwell Dekatron computer first ran at Harwell Atomic Energy Research Establishment in 1951 where it automated the calculations that were being performed by 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.

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