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Both groups of scientists behind the Manchester Mark 1 and Edsac computers employed memory technology that had its origins in World War II radar, but their approaches contrasted significantly.
Edsac's Cambridge designers opted for mercury delay line storage, pictured above with one the system's architects, computing pioneer Sir Maurice Wilkes.
Delay-line memory works by sending audio pulses corresponding to an information pattern through a medium that creates a delay, in this case a tube of mercury. Then the path is looped back on itself through amplifying and timing circuits, forming a closed loop that refreshes the information. Transducers at the end of the line convert between acoustic energy and electrical signals; for these to work effectively, however, the mercury had to be heated to 40° celsius, making the storage compartment a particularly unpleasant place to work.
Photograph © 2008 University of Cambridge Computer Laboratory. Reproduced by permission
Manchester's computer scientists based their Mark 1 system on Williams tube memory — also known as the Williams-Kilburn tube — which uses residual charges on cathode ray tubes to store information. An electron gun scanned across the phosphor created a field of bright dots and dark spaces corresponding to ones and zeros, and if the image was rescanned before it faded then the current through the electron gun changed according to the pattern laid down before.
The tubes were invented by Tom Kilburn and Sir Frederic Williams, pictured above at the Manchester Mark 1 console.
These tubes could hold up to 2,048 bits of data and were faster than mercury delay-line storage, but wore out more quickly.
Among the scientists working on the Manchester Mark 1 project was mathematician Mary Lee Woods who later married fellow team member Conway Berners-Lee. Their son is web pioneer Sir Tim Berners-Lee.
Photograph © The University of Manchester 1998, 1999