2009's major milestone for computing pioneers

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