EDSAC
The EDSAC (Electronic Delay Storage Automatic Computer) ran its first program May 6, 1949, and was constructed by Maurice Wilkes and his team at Cambridge University, based on the EDVAC design report by John von Neumann.
This was not the first stored program computer (see the Manchester Baby), but rather the first practical stored program computer. As soon as it was constructed, it immediately began serving the University's research needs. None of its components were experimental. It used mercury delay liness for memory, and derated vacuum tubes for logic. In 1953, David Wheeler, returning from the University of Illinois, designed an index register as an extension to the original EDSAC hardware.
The project was supported by J. Lyons & Co. Ltd., a British firm, who were rewarded with the first commercial computer, LEO I, based on the EDSAC design.
