1943 AD to 1946 AD |
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| By the mid-1940s, the majority of computers were being
built out of vacuum tubes rather than switches and
relays. Although vacuum tubes were fragile,
expensive, and used a lot of power, they were much faster than relays (and much quieter). If we ignore Atanasoff's machine and COLOSSUS, then the first true general-purpose electronic computer was the electronic numerical integrator and computer (ENIAC), which was constructed at the University of Pennsylvania between 1943 and 1946. |
ENIAC, which was the brainchild of John William Mauchly and J.
Presper Eckert Jr., was a monster. It was 10 feet tall, occupied 1,000 square feet of floor- space, weighed in at approximately 30 tons, and used more than 70,000 resistors, 10,000 capacitors, 6,000 switches, and 18,000 vacuum tubes. The final machine required 150 kilowatts of power, which was enough to light a small town. |
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| One of the greatest problems with computers built from vacuum t ubes was reliability; 90% of ENIAC's down-time was attributed to locating and replacing burnt-out tubes. Records from 1952 show that approximately 19,000 vacuum tubes had to be replaced in that year alone, which averages out to about 50 tubes a day! | ||
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| During the course of developing ENIAC, Mauchly and Eckert recognized a variety of improvements and new techniques, which they determined to use in any subsequent machines. For example, one of the main problems with ENIAC was that it was hard-wired; that is, it did not have any internal memory as such, but needed to be physically programmed by means of switches and dials. | Around the summer of 1943, Mauchly and Eckert discussed the concept of creating a stored-program computer, in which an internal read-write memory would be used to store both instructions and data. This technique would allow the program to branch to alternate instruction sequences based on the results of previous calculations, as opposed to blindly following a pre-determined sequence of instructions. | |
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| Eckert's idea was to use mercury delay lines (which he already knew a great deal about) for the memory. Around the beginning of 1944, Eckert wrote an internal memo on the subject and, in August 1944, Mauchly and Eckert proposed the building of another machine called the electronic discrete variable automatic computer (EDVAC). | ||
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| These notes are abstracted from the book Bebop BYTES Back (An Unconventional Guide to Computers) Copyright Information |
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