nk497 writes: The first working stored-program computer is set to be rebuilt at Bletchley Park, home to the UK's National Museum of Computing. The Electronic Delay Storage Automatic Calculator ran its first programme in 1949, and was two metres high. Its 3,000 vacuum tubes took up four metres of floor space, and it could perform 650 instructions per second. All data input was via paper tape. The EDSAC used mercury-filled tubes for memory, but in the interests of safety, the replica will use an alternative non-toxic substance. Rebuilding it will take four years, and the public can visit to watch the work as it happens.