1944 AD to 1952 AD
The First Stored Program Computer -- EDVAC

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As was previously discussed, If we ignore both Atanasoff's machine and COLOSSUS, then the first true general- purpose electronic computer was the ENIAC, which was constructed at the University of Pennsylvania between 1943 and 1946. However, ENIAC's underlying architecture was very different to that of modern computers. During the course of designing ENIAC, it's creators, John William Mauchly and J. Presper Eckert Jr., conceived the concept of stored program computing. This concept was subsequently documented by Johann (John) von Neumann in his paper which is now known as the First Draft.

(The computer structure resulting from the criteria presented in the "First Draft" is popularly known as a von Neumann Machine, and virtually all digital computers from that time forward have been based on this architecture.)

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In August 1994, Mauchly and Eckert proposed the building of a new machine called the electronic discrete variable automatic computer (EDVAC). Unfortunately, although the conceptual design for EDVAC was completed by 1946, several key members left the project to pursue their own careers, and the machine did not become fully operational until 1952. When it was finally completed, EDVAC contained approximately 4,000 vacuum tubes and 10,000 crystal diodes. A 1956 report shows that EDVAC's average error-free up-time was approximately 8 hours.
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In light of its late completion, some would dispute EDVAC's claim-to-fame as the first stored-program computer.

A small experimental machine (which was based on the EDVAC concept) consisting of 32 words of memory and a 5-instruction instruction set was operating at Manchester University, England, by June 1948.

Another machine called the electronic delay storage automatic calculator (EDSAC) performed its first calculation at Cambridge University, England, in May 1949.

EDSAC contained 3,000 vacuum tubes and used mercury delay lines for memory. Programs were input using paper tape and output results were passed to a teleprinter. Additionally, EDSAC is credited as using one of the first assemblers called "Initial Orders," which allowed it to be programmed symbolically instead of using machine code.

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Last but not least, the first commercially available computer, the universal automatic computer (UNIVAC I), was also based on the EDVAC design. Work started on UNIVAC I in 1948, and the first unit was delivered in 1951, which therefore predates EDVAC's becoming fully operational.
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These notes are abstracted from the book Bebop BYTES Back
(An Unconventional Guide to Computers)
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