Oldest working digital computer

First used in April 1951, the Harwell Dekatron Computer (also known as WITCH - Wolverhampton Instrument for Teaching Computation from Harwell) is the oldest working electronic computer in the world. Currently located at the National Museum of Computing, Bletchley Park, UK, the computer underwent a complete restoration from September 2009 to November 2012. The computer weighs a massive two and a half tons (2,268kg) and comprises 828 Dekatron valves, 480 relays and a bank of six paper tape readers on which programmes are stored. The computer construction started in 1949, and was used for computations relating to atomic energy research from 1951 until 1957. After it became obsolete for nuclear research, scientists at Harwell Atomic Energy Research Establishment offered the computer as a prize to the most innovative continued use. Wolverhampton and Staffordshire College of Technology (Midlands, UK) won this competition and renamed it WITCH. WITCH was used for computer teaching purposes until 1973 when it was shown for a brief period of time at Birmingham Museum of Science and Industry, UK, until it was dismantled for storage. In 2008, a team from the National Museum of Computing 'found' the stored computer and in 2009 a three-year restoration programme was commenced to rebuild the computer at its new home in the museum where it will again be used for educational purposes. Each calculation the machine performs can be watched via the switching Dekatron valves - something impossible to observe in a modern computer. On average, WITCH takes between 5 and 10 seconds to perform a multiplication of two numbers, and can hold a total of only 90 numbers in its memory at any one time.