The world's first operational stored-program computer, running its first program in June 1948. It was designed by T. Kilburn and F. C. Williams at the University of Manchester, UK, commencing in 1946. Several improvements were added and the first realistic problem to be solved by the machine was achieved in April 1949, shortly before EDSAC began operations. It became the world's first commercially available computer when marketed by Ferranti Ltd in 1951 as the Ferranti Mark I. The effectiveness of the machine was due to its use of electrostatic (Williams tube) storage.