The Manchester Baby, originally called the English Small Scale Experimental Machine (ESSEM), was created by Frederic C. Williams, Tom Kilburn, and Geoff Tootill and ran its first program on June 21, 1948. It was the world's first electronic stored-program computer.
Baby was the first working machine to have all the elements necessary in a modern computer and could store its own instructions. Baby took up a whole room.
One interesting fact about the Baby is that a word in the computer's memory could be read, written, or refreshed, in 360 microseconds.