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In a project described as "the computing equivalent of the raising of the Mary Rose", engineers at Bletchley Park intend to restore a 1950s-era computer - featuring a magnificent 112.5 bytes of memory* - to working order.

The machine in question was built at the Atomic Energy Research Establishment at Harwell in Oxfordshire. It was designed in 1949 to automate the job of a human calculating team, whose work was apparently so boring that mistakes became unacceptably frequent.

Kevin Murrell of the National Museum of Computing at Bletchley Park, where the vintage machine will be restored, says "promises for reliability over speed were certainly met – it was definitely the tortoise in the tortoise and the hare fable".

Apparently the old box worked mainly using electromechanical relays, but also featured 900 gas-filled tubes which could each hold a single bit of information* in memory. Paper tape was used both for input and for program storage.

The Harwell machine ran from 1951-57 at the atom lab, which at the time was claimed by the government to be working solely on peaceful uses of nuclear power - though in fact there were also links to the national weapons programme. Official untruthfulness around the subject was a major factor in the birth of the anti-nuclear movement and associated fear of all nuclear technology, a phenomenon which persists to this day.

After retiring from nuclear work, the computer was offered as a prize to the college which could make best use of it. The then Wolverhampton and Staffordshire Technical College (later Wolverhampton University) won and renamed the machine WITCH (Wolverhampton Instrument for Teaching Computing from Harwell). It was used to teach computing students until 1973.

After its second retirement the WITCH was stored at the Birmingham city museums' collections centre until being acquired for restoration this year by the National Museum of Computing. It arrives at Bletchley Park today, and the team there anticipate having it running at full tortoise-like poke in a year's time.

“The team are eager to start the restoration work,” enthuses Murrell. “It’s the computing equivalent of the raising of the Mary Rose and they are up to challenge!"

The ex-WITCH will sit alongside the already rebuilt Colossus cipher-cracking machine of World War Two fame, and the museum says that once running it will be "the oldest original functioning electronic stored program computer in the world". The current title holder is the Pegasus at London's Science Museum, of 1956 vintage**. ®

Update

*Bletchley Park have been in touch to say that in fact the numbers stored by the "Dekatron"/"Decatron" gas-filled things in the WITCH are decimal numbers, not binary, so our extrapolation to bytes is wrong. More detail in the comments.

Bootnote

**The Colossus doesn't count, as it is only an "electronic programmable computer" - the world's first.

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