Harwell computer

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The Harwell computer, later known as the Wolverhampton Instrument for Teaching Computing from Harwell (WITCH), or the Harwell Dekatron Computer, was an early British relay-based computer. From 2009 to 2012, it was restored at the National Museum of Computing, where it is described as "the oldest original functioning electronic stored program computer in the world". The museum hopes to use the computer's visual, dekatron-based memory to teach schoolchildren about computers.

Source: Wikipedia