EDSAC performed its first calculations
6th May 1949
The EDSAC was the world's first stored-program computer to operate a regular computing service. Designed and built at Cambridge University, England, the EDSAC performed its first calculation on 6th May 1949, running a square numbers program written by Beatrice Worsley. It uses paper tape I/O, and is the first stored-program computer to operate a regular computing service. In August the relocation loader is added to the "initial orders" of the EDSAC.
As soon as EDSAC was constructed, it began serving the University's research needs. None of its components were experimental. It used mercury delay lines for memory, and derated vacuum tubes for logic. Input was via 5-hole punched tape and output was via a teleprinter.
Initially registers were limited to an accumulator and a multiplier register. In 1953, David Wheeler, returning from a stay at the University of Illinois, designed an index register as an extension to the original EDSAC hardware.
The EDSAC's memory consisted of 1024 locations, though only 512 locations were initially implemented. Each contained 18 bits, but the first bit was unavailable due to timing restrictions, so only 17 bits were used. An instruction consisted of a five-bit instruction code (designed to be represented by a mnemonic letter, so that the Add instruction, for example, used the bit pattern for the letter A), eleven bits for a memory address (although with 1024 words, only 10 bits were needed), and one bit (for certain instruction) to control whether the instruction operated on a number contained in one word or two.
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