EDVAC (Electronic Discrete Variable Automatic Computer) was to be a vast improvement upon ENIAC, its predecessor. Mauchly and Eckert started working on it two years before ENIAC even went into operation. Their idea was to have the program for the computer stored inside the computer. This would be possible because EDVAC was going to have more internal memory than any other computing device to date. Memory was to be provided through the use of mercury delay lines, the idea being that given a tube of mercury, an electronic pulse could be bounced back and forth to be retrieved at will -another two state device for storing 0s and 1s. This on/off switchability for the memory was required because EDVAC was to use binary rather than decimal numbers, thus simplifying the construction of the arithmetic units.
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