The SSEM 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. The first of the two versions of the Manchester Mark 1 – known as the Intermediary Version – was operational by April 1949. However, this first version lacked features such as the instructions necessary to programmatically transfer data between the main store and its newly developed magnetic backing store, which had to be done by halting the machine and manually initiating the transfer. These missing features were incorporated in the Final Specification version, which was fully working by October 1949. The machine contained 4,050 valves and had a power consumption of 25 kilowatts. To increase reliability, purpose-built CRTs made by GEC were used in the machine instead of the standard devices used in the SSEM.