A computer is a mechanical or electronic device that can efficiently store, retrieve, and manipulate large amounts of information at high speed and with great accuracy. Moreover, it can execute tasks and act upon intermediate results without human intervention by carrying out a list of instructions called a program.

Although we tend to think of the computer as a recent development, Charles Babbage, an Englishman, designed and partially built a true computer in the mid-1800s. Babbage's machine, which he called an Analytical Engine, contained hundreds of axles and gears and could store and process 40-digit numbers. Babbage was assisted in his work by Ada Augusta Byron, the daughter of the poet Lord Byron. Ada Byron grasped the importance of the invention and helped to publicize the project. A major programming language (Ada) was named after her. Unfortunately, Babbage never finished his Analytical Engine. His ideas were too advanced for the existing technology, and he could not obtain enough financial backing to complete the project.

Serious attempts to build a computer were not renewed until nearly 70 years after Babbage's death. Around 1940, Howard Aiken at Harvard University, John Atanasoff, and Clifford Berry at Iowa State University built machines that came close to being true computers. However, Aiken's Mark I could not act independently on its intermediate results, and the Atanasoff-Berry computer required the frequent intervention of an operator during its computations.

Just a few years later in 1945, a team at the University of Pennsylvania, led by John Mauchly and J. Presper Eckert, completed work on the world's first fully operable electronic computer. Mauchly and Eckert named it ENIAC, an acronym for Electronic Numerical Integrator and Computer. ENIAC was a huge machine. It was 80 feet long, 8 feet high, weighed 33 tons, contained over 17,000 vacuum tubes in its electronic circuits, and consumed 175,000 watts of electricity. For its time, ENIAC was a truly amazing machine because it could perform up to 5,000 additions per second with incredible accuracy. However, by current standards, it was exceedingly slow. A modern run-of-the-mill personal computer can exceed 100 million operations per second!

For the next decade or so, all electronic computers used vacuum tubes to do the internal switching necessary to perform computations. These machines, which we now refer to as first-generation computers, were large by modern standards, although not as large as ENIAC. They required a climate-controlled room and lots of tender loving care to keep them operating. By 1995 about 300 computers-built mostly by IBM and Remington Rand-were being used, primarily by large businesses, universities, and government agencies.

By the late 1950s, computers had become much faster and more reliable. The most significant change at this time was that the large, heat-producing vacuum tubes were replaced by relatively small transistors. The transistor is one of the most important inventions of the twentieth century. It was developed at Bell Labs in the late 1940s by William Shockley, John Bardeen, and Walter Brattain, who later shared a Nobel Prize for their achievement. Transistors are small and require very little energy, especially compared to vacuum tubes. Therefore, many transistors can be packed close together in compact enclosure.

In the early 1960s, Digital Equipment Corporation (DEC) took advantage of small, efficient packages of transistors called integrated circuits to create the minicomputer, a machine roughly the size of a four-drawer filing cabinet. Because these computers not only were small but also less expensive than their predecessors, now called mainframes, also rapidly increased. The computer age had clearly arrived and the industry leader was IBM's innovative System 360.