Computer

The first devices that resemble modern computers date to the mid-20th century (1940–1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers Modern computers are based on tiny and are millions to billions of times more capable while occupying a fraction of the space Today, simple computers may be made small enough to fit into a and be powered from a in various forms, are of the and are what most people think of as "a computer"; however, the most common form of computer in use today is the . Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from.

The ability to store and execute lists of instructions called makes computers extremely versatile and distinguishes 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 with capability and complexity ranging from that of a to a are all able to perform the same computational tasks given enough time and storage capacity.

It is difficult to identify any one device as the earliest computer, partly because the term "computer" has been subject to varying interpretations over time. Originally, the term "computer" referred to a person who performed numerical calculations (a ), often with the aid of a . 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 whenThis 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 musicians who play music when struck by operated by a attached to a. The length of and could be re-programmed every day in order to account for the changing lengths of day and night throughout the year