A forerunner of today's computers, the Colossus, which became operational in January 1944, was the first practical electronic digital information processing machine in the world. Code breakers at England's famed Bletchley Park used the computer to help decipher intercepted German signal code messages during the second world war.
You can see a video of the Colossus in action by clicking here.
Among a cohort of talented thinkers assembled at Bletchley Park was the mathematician Alan Turing. Based on his experience working during there, Turing later came up with an idea for a stored-program, electronic computer. Turing also was an early thinker in the field of artificial intelligence.
However, his life took a tragic turn. A homosexual in an era when homosexuality was against the law, Turing was prosecuted in 1952 and accepted chemical castration as an alternative to a jail sentence. He committed suicide just prior to his 42nd birthday. Years later, Britain Prime Minister Gordon Brown apologized for the "appalling" way Turing had been treated for being gay. Time Magazine in 1999 named Turing as one of the 100 Most Important People of the 20th Century.
On Feb. 19, 1946, Alan Turing submitted his now famous "Proposal for the Development in the Mathematics Division of an Automatic Computing Engine" - later known as "ACE" - at a meeting of the National Physical Laboratory in England. It was a breakthrough idea for the time: a design for a stored-program computer. (Here's a video with a couple of Turing's colleagues reminiscing about their work together.)
Four years later, the Pilot ACE, built at England's National Physical Laboratory in 1950, came into being. This was an early version of a computer system Turing had designed. The system, which was state-of-the-art for its time, was an early stored program computer. It used about 800 vacuum tubes and had a clock speed of 1 MHz.
The ENIAC was built to calculate artillery firing tables for the United States Army's Ballistic Research Laboratory. By the time ENIAC was finished, the second world war was already over. But its creators had come up with the first all-electronic machine that could be programmed to perform a variety of tasks. ENIAC also introduced a couple of important concepts for the future of computer science: the "if" statement and the idea of storing programs in a computer's memory.
A replica of the Small-Scale Experimental Machine, which was the world's first stored-program computer in 1948. Although on the small side, it served as proof-of-concept and paved the way for the development of the Manchester Mark 1.
The SWAC (Standards Western Automatic Computer) was an early electronic digital computer built in 1950 by the U.S. National Bureau of Standards. It had 2,300 vacuum tubes and could perform seven basic operations: add, subtract, and multiply (single precision and double precision versions); comparison, data extraction, input, and output.