The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester from the Manchester Baby (operational in June 1948). 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.
![Mark I](https://zkm.de/media/styles/r17_1280/public/bild/2015_-_ausstellung_-_link_-_monster-resurrection.jpg?itok=982TvmN8)