World's oldest digital computer brought back to life

Posted by Emma Woollacott

A 61-year-old computer will today be rebooted, following a three-year restoration project.

The Harwell Dekatron - aka WITCH - computer weighs two and a half tons, and contains 828 flashing Dekatron valves, 480 relays and a bank of paper tape readers. Back in 1951, it was one of perhaps a dozen computers in the world.

"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," says Delwyn Holroyd, of the National Museum of Computing (TNMOC), who led the restoration.

"Older members of the team had to brush up on old skills, while younger members had to learn from scratch!"

The Harwell Dekatron computer first ran at the UK's Harwell Atomic Energy Research Establishment, where it replaced people using mechanical hand calculators.

Designed for reliability rather than speed, it took as much as ten seconds to multiply two numbers. It wasn't even binary, but worked in decimal.

And by 1957, it had become redundant at Harwell, but was given to Wolverhampton and Staffordshire Technical College, which renamed it the WITCH (Wolverhampton Instrument for Teaching Computation from Harwell) and used it in computer education until 1973.

Eventually, though, and after a short stint in a museum, it was dismantled and put into storage, where it was rediscovered in 2008.

"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," says TNMOC trustee Kevin Murrell.

"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."