During the 1950s, semiconductor devices gradually replaced vacuum tubes in digital computers. By 1960 new designs were fully transistorized. Operational in April 1950, the National Bureau of Standards Eastern Automatic Computer (SEAC) employed 10,500 germanium diodes and 747 vacuum tubes.
Working under Tom Kilburn at Manchester University, Richard Grimsdale and Douglas Webb, demonstrated a prototype transistorized computer on November 16, 1953. The 48-bit machine used 92 point-contact transistors and 550 diodes fabricated by STC, the UK arm of ITT. An enhanced version with 250 junction transistors was completed in 1955. The Metropolitan Vickers Electrical Company manufactured six units as the Metrovick 950, which they used commercially within the company from 1956.
Jean H. Felker led a Bell Labs team including engineer James R. Harris that designed and built a fully transistorized computer dubbed TRADIC (TRAnsistor DIgital Computer) for the U. S. Air Force in 1954. Involving about 700 point-contact transistors and over 10,000 diodes, the prototype operated at 1 MHz while requiring less than 100 watts of power. A lighter airborne version (Flyable TRADIC) using junction transistors replaced an analog computer for navigation and bombing control in a C-131 aircraft. Led by William Papian, in April 1956 members of the Advanced Development Group of MIT Lincoln Labs used fast germanium switching transistors from Philco Corporation to build a 5 MHz general-purpose digital computer known as TX-0 (Transistor Experimental). Also in 1956, Japan's first transistorized computer, the ETL Mark III, using 130 point-contact transistors and 1800 diodes was built under the direction of Hiroshi Wada at the Electrotechnical Laboratory in Tokyo.
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