When did the first computer appear?

The first programmable electronic digital computers appeared during the 1940s. Colossus, built in Britain in 1943 and 1944 to break German codes, and ENIAC, completed in the United States in 1945, are often cited as the earliest. ENIAC filled a large room, weighed about 30 tonnes and used around 18,000 vacuum tubes. The conceptual foundations reach back much further: in the 1830s Charles Babbage designed a mechanical Analytical Engine, and Ada Lovelace wrote what is considered the first algorithm intended for it. The invention of the transistor in 1947 and later the microchip shrank computers from room-sized machines to devices that fit in a pocket.