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The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester from the Small-Scale Experimental Machine. Work began in August 1948, and the first version was operational by April 1949; a program written to search for Mersenne primes ran error-free for nine hours on the night of 16/17 June 1949. The machine's successful operation was widely reported in the British press, which used the phrase "electronic brain" in describing it to their readers. The Mark 1 was initially developed to provide a computing resource within the university, to allow researchers to gain experience in the practical use of computers, but it very quickly also became a prototype on which the design of Ferranti's commercial version could be based. Development ceased at the end of 1949, and the machine was scrapped towards the end of 1950, replaced in February 1951 by a Ferranti Mark 1, the world's first commercially available general-purpose computer. The computer is historically significant because of its pioneering inclusion of index registers, an innovation which made it easier for a program to read sequentially through an array of words in memory. Many of the ideas behind its design were incorporated in subsequent commercial products such as the IBM 701 and 702. The chief designers, Frederic C. Williams and Tom Kilburn, concluded from their experiences with the Mark 1 that computers would be used more in scientific roles than in pure mathematics. (Full article...)