A transistor computer, now often called a second-generation computer, is a computer which uses discrete transistors instead of vacuum tubes. The first generation of electronic computers used vacuum tubes, which generated large amounts of heat, were bulky and unreliable. A second-generation computer, through the late 1950s and 1960s featured circuit boards filled with individual transistors and magnetic core memory. These machines remained the mainstream design into the late 1960s, when integrated circuits started appearing and led to the third-generation computer. History The University of Manchester's experimental Transistor Computer was first operational in November 1953 and it is widely believed to be the first transistor computer to come into operation anywhere in the world. There were two versions of the Transistor Computer, the prototype, operational in 1953, and the full-size version, commissioned in April 1955. The 1953 machine had 92 point-contact transistors and 550 diodes, manufactured by STC. It had a 48-bit machine word. The 1955 machine had a total of 200 point-contact transistors and 1,300 point diodes, which resulted in a power consumption of 150 watts. There were considerable reliability problems with the early batches of transistors and the average error-free run in 1955 was only 1.5 hours. The Transistor Computer also used a small number of tubes in its clock generator, so it was not the first fully transistorized machine. The design of a full-size Transistor Computer was subsequently adopted by the Manchester firm of Metropolitan-Vickers, who changed all the circuits to use more reliable junction transistors. The production version was known as the Metrovick 950 and was built from 1956 to the extent of six or seven machines, which were "used commercially within the company" or "mainly for internal use". Other early machines During the mid-1950s a series of similar machines appeared. These included the Bell Laboratories TRADIC, completed in January 1954, which used a single high-power output vacuum-tube amplifier to supply its 1-MHz clock power. The first fully transistorized computer was either the Harwell CADET, which first operated in February 1955, although the price paid for this was that it operated only at the slow speed of 58 kHz, or the prototype IBM 604 transistor calculator. The Burroughs Corporation claimed the SM-65 Atlas ICBM / THOR ABLE guidance computer (MOD 1) that it delivered to the US Air Force at the Cape Canaveral missile range in June 1957 was "the world's first operational transistorized computer". MIT's Lincoln