The practical construction of a von Neumann computer depended on the availability of a suitable memory device. The University of Manchester's Baby, the world's first electronic stored-program computer, had successfully demonstrated the practicality of the stored-program approach and of the Williams tube, an early form of computer memory based on a standard cathode ray tube (CRT), by running its first program on 21 June 1948. Early electronic computers were generally programmed by being rewired, or via plugs and patch panels; there was no separate program stored in memory, as in a modern computer. It could take several days to reprogram ENIAC, for instance. Stored-program computers were also being developed by other researchers, notably the National Physical Laboratory's Pilot ACE, Cambridge University's EDSAC, and the US Army's EDVAC. The Baby and the Mark 1 differed primarily in their use of Williams tubes as memory devices, instead of mercury delay lines. From about August 1948, the Baby was intensively developed as a prototype for the Manchester Mark 1, initially with the aim of providing the university with a more realistic computing facility. In October 1948, UK Government Chief Scientist Ben Lockspeiser was given a demonstration of the prototype Mark 1 while on a visit to the University of Manchester. Lockspeiser was so impressed by what he saw that he immediately initiated a government contract with the local firm of Ferranti to make a commercial version of the machine, the Ferranti Mark 1. In his letter to the company, dated 26 October 1948, Lockspeiser authorised the company to "proceed on the lines we discussed, namely, to construct an electronic calculating machine to the instructions of Professor F. C. Williams". From that point on, development of the Mark 1 had the additional purpose of supplying Ferranti with a design on which to base their commercial machine. The government's contract with Ferranti ran for five years from November 1948, and involved an estimated £35,000 per year (equivalent to £ per year in ). The Baby had been designed by the team of Frederic C. Williams, Tom Kilburn and Geoff Tootill. To develop the Mark 1 they were joined by two research students, D. B. G. Edwards and G. E. Thomas; work began in earnest in August 1948. The project soon had the dual purpose of supplying Ferranti with a working design on which they could base a commercial machine, the Ferranti Mark 1, and of building a computer that would allow researchers to gain experience of how such a machine could be used in practice.