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A Computer is an electronic machine which is used for storing and manipulating the data according to a program .In early days the size of computer is large room size and also consuming much power. The ability to store and execute a program makes distinguishes from calculator.

Computers have at least one CPU that performs most calculations and includes a main memory, a control unit, and an arithmetic logic unit. Increasingly, personal computers contain specialized graphic processors, with dedicated memory, for handling the computations needed to display complex graphics, such as for three-dimensional simulations and games. Auxiliary data storage is usually provided by an internal hard disk and may be supplemented by other media such as floppy disks or CD-ROMs. Peripheral equipment includes input devices, keyboard, mouse and output devices, monitor, printer, as well as the circuitry and cabling that connect all the components.

Generations of computers are characterized by their technology. First-generation digital computers, developed mostly in the U.S. after World War II, used vacuum tubes and were enormous. The second generation, introduced 1960, used transistors and was the first successful commercial computers. Third-generation computers late 1960s and 1970s were characterized by miniaturization of components and use of integrated circuits. The microprocessor chip, introduced in 1974, defines fourth-generation computers.

A general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices. These parts are interconnected by busses, often made of groups of wires. The control unit, ALU, registers, and basic I/O and often other hardware closely linked with these is collectively known as a central processing unit .Early CPUs were comprised of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.

Computers have been used to coordinate information in multiple locations since the 1950s.In the 1970s, computer engineers at research institutions throughout the US began to link their computers together using telecommunications technology. This effort was funded by ARPA now DARPA and the computer network that it produced were called the ARPANET. The technologies that made the Arpanet possible spread and evolved. In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer.

The network is the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web like e-mail and the World Wide Web.

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