Generally, a computer is any electronic data-processing device that performs tasks, such as mathematical calculations or electronic communication, under the control of a set of instructions called a program. Programs usually reside within the computer's main memory and are retrieved and processed by the computer's electronics, and the program results are stored or routed to output devices, such as video display monitors or printers. It communicates with other electronic devices to receive data, store and manipulate them (using mathematical and logical calculations specified in a sequence of instructions called a program), and transmit the results; e.g. accept a sequence of numbers typed in at a keyboard, and plot a graph of them on a visual display unit, or monitor.

Computers are now familiar at work, home, and school, as desktop personal computers (PCs). They also exist as very small devices called microprocessors, to control electronic equipment and machinery, e.g. car engines; and as much larger devices such as supercomputers, used to model and predict weather, earthquakes, nuclear explosions, etc.
The heart of today's computers are integrated circuits (ICs), sometimes called microchips, or simply chips. These tiny silicon wafers can contain millions of microscopic electronic components and are designed for many specific operations: some control an entire computer (CPU, or central processing unit, chips); some perform millions of mathematical operations per second (math coprocessors); others can store more than 16 million characters of information at one time (memory chips).

Computer Types
General-purpose computers, such as personal computers and business computers, are very versatile because they can accept new sets of instructions. Each new set of instructions, or program, enables the same computer to perform a different type of operation. For example, one program lets the computer act like a word processor, another lets it manage inventories, and yet another transforms it into a video game.

Embedded
Special-purpose, or dedicated, computers are designed to perform specific tasks. Their operations are limited to the programs built into their microchips. An embedded system is dedicated to one specific task. They are special purpose systems. These microprocessors are the basic components of electronic calculators and can be found in many other electronic products, including cameras, digital watches, and automobiles. These computers are the basis for electronic calculators and can be found in thousands of other electronic products, including digital watches (controlling timing, alarms, and displays), cameras (monitoring shutter speeds and aperture settings), and automobiles (controlling fuel injection, heating, and air conditioning and monitoring hundreds of electronic sensors). Embedded systems typically have their programs stored in ROM as opposed to auxiliary storage and RAM.

Microcomputers
These are computers which uses a microprocessor as its CPU.
Notebook
Although some general-purpose computers are as small as pocket radios, the smallest class of fully functional, self-contained computers is the class called notebook computers. These usually consist of a CPU, data-storage devices called disk drives, a liquid-crystal display (LCD), and a full-size keyboard--all housed in a single unit small enough to fit into a briefcase.

Desktop PCs
Today's desktop personal computers, or PCs, are many times more powerful than the huge, million-dollar business computers of the 1960s and 1970s. Most PCs can perform from 16 to 66 million operations per second, and some can even perform more than 100 million. These computers are used not only for household management and personal entertainment, but also for most of the automated tasks required by small businesses, including word processing, generating mailing lists, tracking inventory, and calculating accounting information.