Metrovick 950
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The Metrovick 950 was the first commercial transistorized computer, built from 1959 onwards by British company Metropolitan-Vickers to the extent of seven machines. The 950 appears to have been Metrovick's first and last commercial computer offering.
The 950 design started as an experimental machine built at Manchester University in order to test the suitability of transistors in improving the reliability of the Manchester Mark I computer. The resulting machine was otherwise similar to the Mark I, except that it did not include Williams tubes and used only the magnetic drum for main memory. The machine was based on a 48-bit word, although 4 bits were used for timing and thus not available for program use. The Metrovick 950 had a clock frequency of 125 kHz (= 1/8 MHz).
After successfully building the prototype in November 1953, it was re-built with a Mark I-style B-line accumulator/index register and hardware multiplier. The new model ran for the first time in 1955. The added circuitry brought the machine to a total of 250 transistors, up from the prototype's 92. The Metrovick 950 used only 150 watts of power, an astonishingly low figure in an era when machines typically used tens of kilowatts to warm their tubes. The new model could add two 44-bit numbers in 1.5 drum revolutions, which, at a drum spin rate of 3000 RPM, amounted to roughly 30 milliseconds per addition. Although faster than the Mark I internally, the lack of Williams tubes made the Metrovick 950 run much slower; the Mark I could add two 40-bit numbers in 1.8 milliseconds.
Metrovick became interested in the design after the success the university had selling computing time on the Mark I to commercial customers. Their commercial versions used newer junction transistors (as opposed to point-contact ones) for added reliability, although it appears at least one was built with the earlier components.
