Manchester Baby

Officially the Small-Scale Experimental Machine, it was built not to compute but to prove that a cathode-ray tube could serve as memory. The Williams-Kilburn tube stored bits as charge spots on the inside of the screen and read them back as an image; the whole memory held 32 words of 32 bits, about 128 bytes. Proving the tube was the point; the machine around it becoming the world's first stored-program computer was almost a side effect.

The first program, written by Tom Kilburn, searched for the highest proper factor of 2¹⁸ by trying candidates downwards. It ran for 52 minutes and gave the right answer. Within three years the design had grown into the Ferranti Mark 1, the first commercially sold general-purpose computer, which Alan Turing among others programmed at Manchester.