The Manchester Small-Scale Experimental Machine (SSEM), nicknamed Baby, was the world's first stored-program computer. It was developed at the Victoria University of Manchester by Frederic C Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948.
The machine was designed and built as a test-bed for the Williams tube, an early form of computer memory, not as a practical computer. However, its success resulted in its further development to become the Manchester Mark 1 computer, which in turn led directly to the development of the Ferranti Mark I, the world's first commercially available general-purpose computer.
The SSEM had a 32-bit word length and a main store of 32 words. Three bits were used to hold the instruction code, giving a maximum of eight instructions, of which only seven were defined. Three programs were written for the SSEM, the first of which, to calculate the highest factor of 218, consisted of 17 instructions and took 52 minutes to reach the answer after performing 3.5 million operations.