The Machine That Remembered Instructions

On June 21, 1948, at the University of Manchester, a machine executed a program stored in its own electronic memory. Officially the Small-Scale Experimental Machine, everyone called it the Baby. It was the first computer to run a stored program. Before the Baby, programs were wired into machines. After the Baby, programs became data.

The concept had been described by Alan Turing. The Manchester team -- Freddie Williams and Tom Kilburn -- built the first physical implementation. The Baby had 32 words of memory, each 32 bits, and could perform seven operations. The first program found the highest factor of a number. It took 52 minutes. The answer was correct.

a cathode ray tube (williams tube) -- the type of memory used in the manchester baby to store its program and data as electronic dots on a screen. source: wikimedia commons

The breakthrough was the Williams-Kilburn tube, a CRT used as random-access memory. It stored both program and data in the same space, treating instructions as another type of data. This was stored-program architecture -- the foundation of every general-purpose computer since. If instructions could be stored in memory, they could be modified by the machine itself. Programs could rewrite themselves. Loops, conditionals, and subroutines became possible.

The Baby was a proof of concept, later refined into the Manchester Mark 1 and commercialized as the Ferranti Mark 1. Kilburn later said the significance was not immediately obvious. He was solving a specific problem. That every smartphone, server, and supercomputer would follow the same design was not something he anticipated. The world changed as a side effect.