Ferranti Mark I

The Ferranti Mark 1, also known as the Manchester Electronic Computer in its sales literature, and thus sometimes called the Manchester Ferranti, was the world's first commercially available general-purpose electronic computer. It was "the tidied up and commercialised version of the Manchester computer". The first machine was delivered to the Victoria University of Manchester in February 1951, ahead of the UNIVAC I, which was supplied to the United States Census Bureau on 31 March 1951, although not delivered until late December the following year.

Based on the Manchester Mark 1, which was designed at the University of Manchester by Freddie Williams and Tom Kilburn, the machine was built by Ferranti of the United Kingdom. The Manchester Mark 1 effectively served as a prototype for the Ferranti Mark 1; the main improvements over it were in the size of the primary and secondary storage, a faster multiplier, and additional instructions.

The Mark 1 used a 20-bit word stored as a single line of dots of electric charges settled on the surface of a Williams tube display, each cathodic tube storing 64 lines of dots. Instructions were stored in a single word, while numbers were stored in two words. The main memory consisted of eight tubes, each storing one such page of 64 words. Other tubes stored the single 80-bit accumulator (A), the 40-bit "multiplicand/quotient register" (MQ) and eight "B-lines", or index registers, which was one of the unique features of the Mark 1 design. The accumulator could also be addressed as two 40-bit words. An extra 20-bit word per tube stored an offset value into the secondary storage. Secondary storage was provided in the form of a 512-page magnetic drum, storing two pages per track, with about 30 milliseconds revolution time. The drum provided eight times the storage of the original designed at Manchester.

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