Bletchley to restore oldest working computer

The National Museum of Computing is to host the restoration of Witch, the world's oldest working modern computer

On Thursday, The National Museum of Computing at Bletchley Park will become the home of Witch, a 1951 computer first used in atomic research.

A year of restoration is planned, after which Witch — also known as the Harwell Machine — will become the world's oldest functioning stored program electronic computer.

Witch — the Wolverhampton Instrument for Teaching Computing From Harwell — is a unique design based around telephone exchange relays and 900 dekatrons, neon-filled valves that can store one of 10 numbers. It was designed, built and first used by the Atomic Energy Research Establishment in Harwell, Oxfordshire, and was subsequently moved to academic use in Wolverhampton, where it remained in service until 1973.

Although not the oldest electronic calculating device, it is regarded as the first modern computer still capable of working, as it can operate from a stored program held in the same memory as the data on which it works.

Witch was extremely slow by modern standards, taking up to 10 seconds to complete a single multiplication. However, it was extremely reliable and, if given sufficient reserves of paper tape for input and output, could run for more than a week without attention. In use, it replaced human mathematicians who would otherwise have to calculate large tables of numbers.

Kevin Murrell, a director and trustee of TNMOC, said in a statement: "Its promises for reliability over speed were certainly met — it was definitely the tortoise in the tortoise and the hare fable. In a race with a human mathematician using a mechanical calculator, the human kept pace for 30 minutes, but then had to retire exhausted as the machine carried on remorselessly. The machine once ran for 10 days unattended over a Christmas/New Year holiday period."

The Bletchley Park restoration will be funded by the sale of 25 shares at £4,500 apiece to members of the public and industry companies wishing to sponsor the project, with the first share going to business process optimisation house Insight Software.


A 1950s mathematician inspects the paper tape from the Harwell Machine, soon to be housed at Bletchley Park
Image courtesy of Wolverhampton Express and Star


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