Harwell Dekatron / WITCH
The Harwell Dekatron computer first ran in 1951 and by great fortune still exists today and is currently being restored in association with the CCS (Computer Conservation Society) in full public view in the Large Systems Room in TNMOC.
The history of the Harwell Dekatron is fascinating. In 1951 it was one of only a handful of computers in the world, and by 1973 it was acclaimed the world's most durable computer. When the current restoration is complete it will be the oldest original working digital computer in the world - a record that is likely to stand for as long as it continues to function.
Between late 2009 and 2012, a TNMOC team of volunteers has been using its ingenuity and re-engineering skills to restore this record-breaking computer.
The machine was rebooted on 20 November 2012 in the presence of two of the original designers and two former users.
You can read the complete story of the world's oldest working digital computer in a book published by TNMOC.