New book: The Harwell Dekatron Computer

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New TNMOC book tells the story of the world's oldest working digital computer

The National Museum of Computing has published a book tracing the fascinating and varied history of the Harwell Dekatron / WITCH, the world's oldest working digital computer, which was restored and rebooted at the Museum in 2012.

The Harwell Dekatron Computer, by Kevin Murrell who rediscovered the Dekatron computer, and Delwyn Holroyd, who led the restoration team that brought the machine back to life, tells the story of the machine that has led a charmed life and defied the recyclers across seven decades to find a practical use again in 2013. It draws on the memories of many of those involved with the machine across the years from the original designers through users across the years to today's conservation team.

Designed in 1949 and first operational in 1951, the Harwell Dekatron was one of perhaps a dozen computers in the world at that time. As big as the wall of a living room, it clattered and flashed as it performed the work of human "computors" using hand calculators at Harwell from 1951-57.

Instead of being consigned to the recyclers when it became obsolete, it was offered in a competition to the educational establishment proposing the best use for it. Wolverhampton Institute of Technology recognised its potential in education, won the machine and renamed it the WITCH (the Wolverhampton Instrument for Teaching Computation from Harwell). It operated there until 1973 when it was retired for a second time to a Birmingham museum and subsequently dismantled and left largely forgotten in safe storage.

Rediscovered by chance by TNMOC trustee Kevin Murrell in 2008, it was brought to TNMOC where it was restored and brought back to life much to the amazement of the world's media in November 2012.

Today, apart from being a star attraction at TNMOC, it is again used in education to show the beginnings of our information age and to enable students to see the dramatic inner workings of the world's oldest working digital computer.

The Harwell Dekatron Computer book, with 40 pages and more than 50 period and modern images, is available onsite at The National Museum of Computing shop for £6 and through

Buy the book here

Notes To Editors

About The National Museum of Computing

The National Museum of Computing, located at Bletchley Park, is an independent charity housing the largest collection of functional historic computers in Europe, including a rebuilt Colossus, the world’s first electronic semi-programmable computer. The Museum enables visitors to follow the development of computing from the ultra-secret pioneering efforts of the 1940s through the mainframes of the 1960s and 1970s, the rise of personal computing in the 1980s and beyond.

New working exhibits are regularly unveiled and the public can already view a rebuilt and fully operational Colossus, the restoration of the Harwell Dekatron / WITCH computer, an ICL 2966, one of the workhorse mainframes computers of the 1980s, many of the earliest desktops of the 1980s and 1990s, plus the NPL Technology of the Internet Gallery.

Funders of the Museum include Bletchley Park Capital Partners, CreateOnline, Ceravision,, Google UK, PGP Corporation, IBM, NPL, HP Labs, BCS, the Drapers' Foundation, Black Marble, and the School of Computer Science at the University of Hertfordshire.

The Museum is currently open to the public on Thursdays and Saturdays from 1pm, and on Bank Holidays in spring and summer. Guided tours are also available at 2.30pm on Tuesdays, 2pm Sundays and some other days. Groups may visit at other times by arrangement and special organisation Away-Days can be booked.

For more information, see and follow @tnmoc on Twitter and The National Museum of Computing on Facebook and Google+.

Media Contacts
Stephen Fleming
Palam Communications for TNMOC
t +44 (0) 1635 299116

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