The machine, which measures 20ft by 22ft, was originally used by London University to organise the grades of A and O-level exam results and print certificates. After it was replaced by new technology, 'Flossie' was then sold to a group of students before being passed on to two enthusiasts who have been restoring it in a large garden shed in Ashford, Kent.
Each piece of memory was handwired with pieces of wire threaded through the machine.
Roger Holmes, a volunteer for the Computer Conservation Society, said: "It is a unique piece of history. People who come to see it are so amazed by it, that computers were ever so big. It's important as it puts modern stuff in context."
VIDEO: It doesn't do Twitter, it doesn't do Facebook - but hidden away in an old barn is what's believed to be the UK's oldest working computer. Sarah Saunders met Roger Holmes and Rodney Brown.