Man vs Machine at Computer Museum: WITCH is faster

Summary:After the world's oldest working digital computer was rebooted at The National Museum of Computing at Bletchley Park last week, it showed its paces in a race against a man with a hand-cranked Facit mechanical calculator.

After the world's oldest working digital computer was rebooted at The National Museum of Computing at Bletchley Park last week , it showed its paces in a race against a man with a hand-cranked Facit mechanical calculator.

In the long run, obviously, even the slowest computer will win: unlike a human, it can keep going forever, or at least until it crashes. But the battle took me back to my student days, before electronic calculators were widely available...

When I was at university in the late 1960s, I was fortunate to get a holiday job with the Ideal Insurance Company in Birmingham. Until then, I'd done calculations in the usual way, with log tables and slide rules. In the Ideal's actuarial department, however, we used hand-cranked Facit mechanical calculators. This led to some sharing of tips and tricks, and the inevitable races, where two or three of us would see who was quickest to complete a complex calculation.

Bart Fossey reputedly did the same kind of thing almost 60 years ago, except he raced the Harwell Dekatron computer. It was a race he repeated with a Facit when the restored machine was restarted at TNMOC, making it the world's oldest working digital computer.

Bart Fossey with Peter Burden and WITCH computer
Bart Fossey re-enacts the "race" with a Facit calculator. WITCH is in the background. Peter Burden of Wolverhampton looks on. Photo: TNMOC

However, Fossey says the old story is not quite true. He was actually using the Facit to check that the computer's rounding errors were not leading to a false result. He realised from the sound of the machine that they were performing the calculations at the same rate.

A Dekatron tube (not called a "valve" even in he UK)
A Dekatron tube Credit: TNMOC

This wouldn't happen with a binary computer, but as its name suggests, the Harwell Dekatron does its calculations in tens rather than twos, just like a pin-wheel calculator. (A Dekatron cold cathode counting tube can store any number from 0 to 9.)

Any Facit user will know that its operation requires some manual dexterity, and you get can really fast if you use one for several hours a day. Fossey was obviously short of practice, but TNMOC says he "managed to keep up with the machine for several minutes to great acclaim from the audience".

The Harwell Dekatron was designed at the Atomic Energy Research Establishment in Harwell, constructed from standard off-the-shelf Post Office components, and started operating in 1951. Luckily, it avoided the fate of other early devices, which were typically broken up so their parts could be re-used.

When the Computer Conservation Society's restoration project started in 2009, TNMOC's Kevin Murrell told me: "It's led a charmed life. It was used at Harwell for about seven years, and then they started buying commercial equipment. It was offered as a prize to the educational institution that could come up with the best case for having the machine, and Wolverhampton College of Technology won. They treasured the machine and kept it in tiptop condition from 1957 until 1973, when it went to Birmingham Science Museum. They displayed it for four or five years, I think, before putting it into storage." (See: Ding dong, this Witch ain't dead.)

The Wolverhampton interlude gave the Dekatron its other name: WITCH stands for Wolverhampton Instrument for Teaching Computation from Harwell.

The Harwell Dekatron/WITCH should now run for many more years, but not forever: eventually we'll run out of working tubes. At that point yes, a Facit will be faster.



The Harwell Dekatron/WITCH coming back into life at The National Museum of Computing on 20 November 2012 

Topics: United Kingdom, After Hours, Hardware


Jack Schofield spent the 1970s editing photography magazines before becoming editor of an early UK computer magazine, Practical Computing. In 1983, he started writing a weekly computer column for the Guardian, and joined the staff to launch the newspaper's weekly computer supplement in 1985. This section launched the Guardian’s first webs... Full Bio

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