Amazing! From David Pescovitz … 1951 digital computer restored and rebooted:
Wolverhampton Instrument for Teaching Computation (WITCH), a 61-year-old machine that was rebooted yesterday to become "the world's oldest original working digital computer." Originally operated at the Harwell Atomic Energy Research Establishment, it was moved in 1957 to Wolverhampton's Staffordshire Technical College where it was dubbed the WITCH. There it stayed until retirement in 1973 when it became a museum display before dismantling for storage. In 2008, the National Museum of Computing in Bletchley Park began to restore the valve-laden beast.