In 1936 British mathematician Alan Turing proposed the idea of a machine that could process equations without human direction. The machine (now known as a Turing machine) resembled an automatic typewriter that used symbols for math and logic instead of letters. Turing intended the device to be used as a "universal machine" that could be programmed to duplicate the function of any other existing machine. Turing's machine was the theoretical precursor to the modern digital computer.
In the 1930s American mathematician Howard Aiken developed the Mark I calculating machine, which was built by IBM. This electronic calculating machine used relays and electromagnetic components to replace mechanical components. In later machines, Aiken used vacuum tubes and solid state transistors (tiny electrical switches) to manipulate the binary numbers. Aiken also introduced computers to universities by establishing the first computer science program at Harvard University. Aiken never trusted the concept of storing a program within the computer. Instead his computer had to read instructions from punched cards.
John Mauchly, an American physicist, and J. Presper Eckert,
an American engineer, proposed an electronic digital computer, called the Electronic Numerical Integrator And Computer (ENIAC), which was built at the Moore School of Engineering at the University of Pennsylvania in Philadelphia. The computer was based on some concepts developed by John Atanasoff, a physics teacher at Iowa State College. ENIAC was completed in 1945 and is regarded as the first successful, general digital computer. It weighed more than 27,000 kg (60,000 lb), and contained more than 18,000 vacuum tubes.
Roughly 2000 of the computer's vacuum tubes were replaced each month by a team of six technicians. Many of ENIAC's first tasks were for military purposes, such as calculating ballistic firing tables and designing atomic weapons. Since ENIAC was initially not a stored program machine, it had to be reprogrammed for each task.
Unfortunately, although the conceptual design for EDVAC was completed by 1946, several key members including Eckert and Mauchley 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.
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.
Eckert and Mauchley eventually formed their own company, which was then bought by the Rand Corporation. They produced the Universal Automatic Computer (UNIVAC), which was used for a broader variety of commercial applications. The (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.
Eckert and Mauchly later lost the patent on their machine when it was claimed that another early experimenter, John Atanasoff, had given them all the ideas about ENIAC that mattered.
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