Although the development of digital computers is rooted in the abacus and early mechanical calculating devices, Charles Babbage is credited with the design of the first modern computer, the "analytical engine," during the 1830s. Vannevar Bush built a mechanically operated device, called a differential analyzer, in 1930; it was the first general-purpose analog computer. John Atanasoff constructed the first electronic digital computing device in 1939; a full-scale version of the prototype was completed in 1942 at Iowa State College (now Iowa State Univ.). In 1943 Conrad Zuse built the Z3, a fully operational electromechanical computer.
During World War II, the Colossus was developed for British codebreakers; it was the first programmable electronic digital computer. The Mark I, or Automatic Sequence Controlled Calculator, completed in 1944 at Harvard by Howard Aiken, was the first machine to execute long calculations automatically, while the first all-purpose electronic digital computer, ENIAC (Electronic Numerical Integrator And Calculator), which used thousands of vacuum tubes, was completed in 1946 at the Univ. of Pennsylvania. UNIVAC (UNIVersal Automatic Computer) became (1951) the first computer to handle both numeric and alphabetic data with equal facility; intended for business and government use, this was the first widely sold commercial computer.
First-generation computers were supplanted by the transistorized computers (see transistor) of the late 1950s and early 60s, second-generation machines that were smaller, used less power, and could perform a million operations per second. They, in turn, were replaced by the third-generation integrated-circuit machines of the mid-1960s and 1970s that were even smaller and were far more reliable. The 1970s, 80s, and 90s were characterized by the development of the microprocessor and the evolution of increasingly smaller but powerful computers, such as the personal computer and personal digital assistant (PDA), which ushered in a period of rapid growth in the computer industry.
The World Wide Web was unveiled in 1990, and with the development of graphical web browser programs in succeeding years the Web and the Internet spurred the growth of general purpose home computing and the use of computing devices as a means of social interaction. Smartphones, which integrate a range of computer software with a cellular telephone that now typically has a touchscreen interface, date to 2000 when a PDA was combined with a cellphone. Although computer tablets date to the 1990s, they only succeeded commercially in 2010 with the introduction of Apple's iPad, which built on software developed for smartphones.