The Small Scale Experimental Machine, the Baby, was built in 1947 and 1948 to subject the Williams-Kilburn Tube to a searching test of its speed and reliability. It also demonstrated the feasibility and potential of a stored-program computer. It was quickly decided to press ahead to develop a realistic useable computer based on the same principles. As early as October 1948 a request was made from the government to Ferranti Ltd. to manufacture a commercial machine to Prof. Williams’ specification.
By the Autumn of 1949 the engineering team had produced a working computer with a larger store and more powerful instruction set, and with the addition of a hardware multiplier, address modification registers (“B-lines”), a two-level store comprising a set of Williams-Kilburn Tubes and a Magnetic Drum Store, and input/output from/to 5-hole paper-tape teleprinter. To improve reliability for the CRT store they were now using CRTs specially manufactured for them by GEC (with the particular assistance of Laurie Allard). With a programmable fast drum connected as well, this was the first working two-level store.