The EDSAC project is now really starting to show results after meticulous research and preparatory work. The first four of the eventual 12 racks of electronics are about to be installed and visitors will soon be able to see the reconstruction in action.
The reconstruction of EDSAC will occupy one end of what is coming to be known as the First Generation Gallery. It will face the 1951 Harwell Dekatron / WITCH computer at the other end of the gallery and provide a stunning introduction about early computing for visitors.
Beginning the reconstruction of EDSAC at TNMOC
Rack design work has been completed and the first four are about to be installed in the new gallery. These racks should be well-populated in time for a very well-known peak time television programme scheduled to feature EDSAC as part of an early computing feature in late February.
The chassis or "shelves" of electronics that comprise each functional EDSAC unit, such as the Clock Pulse Generator, Digit Pulse Generators, Store Regeneration Units and Half Adders, are being designed, assembled and tested by volunteers around the UK. Of the 140 chassis required, 40 have been completed and tested stand-alone; others are currently being assembled.
Some of the Store Regeneration Units are being built for the project free-of-charge by Marshall Amplification Ltd, “The Home of Loud”, which is based in Bletchley. The valve technology, construction techniques and craft skills that produce high-end customised amplifiers for some of the world’s best-known rock bands are remarkably similar to what we need for the EDSAC reconstruction!
The delay lines used for the replica will be nickel rather than mercury for reasons of cost and health and safety. This slightly later technology will also be less temperature-sensitive and therefore more reliable in the museum environment.
EDSAC's main power supply units have also now arrived on site. These are not trivial components, as EDSAC was power-hungry and required over 10kW. These modern units will power up the replica slowly and automatically to avoid damaging any of its 3,000 valves, something that had to be done manually and very carefully by operators of the original EDSAC.
Work on reconstructing EDSAC in situ is expected to begin in March and changing displays will inform visitors of progress. On certain days, visitors will even see the reconstruction in progress as volunteers undertake the work in view of the public.