Computer, electronic device ability of performing a series of arithmetic or logical operations. computer is a machine that handles data according to a set of instructions. Computer is distinguished from electronic calculator, by the number and complexity of the operations it can act by its ability to store a program and retrieve information in its memory without human interference.
Programmable machine that can store, recover and process data. Computers have at least one CPU that executes most calculations and includes a main memory, a control unit and an arithmetic logic unit. Personal computers contain specialized graphic processors, with devoted memory, for handling the computations needed to display complex graphics, such as for three-dimensional imitations and games.

Supplementary 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 apparatus includes input devices ( keyboard, mouse) and output devices ( monitor, printer), as well as the circuitry and cabling that connect all the parts. Computers generations are designated by their technology. First-production digital computers, developed in the U.S. After World War II, used vacuum tubes and were very large. The second production, introduced c. 1960, used transistors and were the first profitable commercial computers. Third-production 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.

Analog computer performs information as physical quantities and functions on the information by controling the quantities. It is device to process information in which the variable quantities change continuously; it changes the linkages between the variables of a difficulty into analogous linkages between electrical quantities, such as current and voltage and resolves the original difficulty by solving the same problem, or analog, that is start in its electrical circuits.

Computer main parts are arithmetic and logic unit, control unit, memory and the input and output devices. These computers parts are jointed by busses, commonly made of sets of wires.Control unit, ALU, registers and basic I/O are collectively known as a central processing unit. Central processing unit were possessed of many separate parts but since the mid-1970s CPUs have commonly assembled on a distinct integrated circuit called a microprocessor.

Different types of Computer Systems:

1) Handheld Single User
2) Portable Single User
3) Thin Client Single User
4) Desktop Single User
5) Workstation Single User
6) Embedded Dedicated Task
7) Server - Multi User
8) Mainframe
9) Super Computer