computer

Although mechanical examples of computers have existed through much of recorded human history, the first resembling a modern computer were developed in the mid-20th century (1940–1945). The first electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers ( Modern computers based on tiny are millions to billions of times more capable than the early machines, and occupy a fraction of the space. Simple computers are small enough to fit into a , and can be powered by a their various forms are of the , what most people think of as a "computer", but the in devices ranging from to , , and the most numerous.

The ability to store and execute lists of instructions called makes computers extremely versatile, distinguishing them from . The is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore computers ranging from a to a are all able to perform the same computational tasks, given enough time and storage capacity.

The first use of the word "computer" was recorded in 1613, referring to a person who carried out calculations, or computations, and the word continued to be used in that sense until the middle of the 20th century. From the end of the 19th century onwards though, the word began to take on its more familiar meaning, describing a machine that carries out computations.

The history of the modern computer begins with two separate technologies—automated calculation and programmability—but no single device can be identified as the earliest computer, partly because of the inconsistent application of that term. Examples of early mechanical calculating devices include the the and arguably the and the (which dates from about 150–100 BC). (c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when. This is the essence of programmability.

The "castle clock", an invented by in 1206, is considered to be the earliest . It displayed the , the and , a -shaped travelling across a gateway causing to open every and five who played music when struck by operated by a attached to a The length of and could be re-programmed to compensate for the changing lengths of day and night throughout the year.

The end of the saw a re-invigoration of European mathematics and engineering. device was the first of a number of mechanical calculators constructed by European engineers, but none fit the modern definition of a computer, because they could not be programmed.