Wednesday, 16 November 2011


Now they come in a variety of shapes and sizes, which can be classified according to their processing power: supercomputers, mainframe computers, workstations, microcomputers, and microcontrollers.

supercomputers are high-capacity machines with thousands of processors that can perform more than several trillion calculations per second.These are the most expensive and fastest computers available.More recently they have been employed for business purposes—for instance, sifting demographic marketing information—and for creating film animation. 

The only type of computer available until the late 1960s, mainframes are water- or air-cooled computers that are vary in size from small, to medium, to large, depending on their use. Mainframes are used by large organizations—such as banks, airlines, insurance companies, and colleges—for processing millions of transactions.Often users access a mainframe by means of a terminal, which has a display screen and a keyboard and can input and output data but cannot by itself process data. Mainframes process billions of instructions per second. 

Introduced in the early 1980s, workstations are expensive, powerful personal computers usually used for complex scientific, mathematical, and engineering calculations and for computer-aided design and computer-aided manufacturing. Providing many capabilities comparable to those of midsize mainframes, workstations are used for such tasks as designing airplane fuselages, developing prescription drugs, and creating movie special effects.Workstations have caught the eye of the public mainly for their graphics capabilities, which are used to breathe three-dimensional life into movies such as WALL⋅E and Harry Potter.The capabilities of low-end workstations overlap those of high-end desktop microcomputers.

Microcomputers, also called personal computers (PCs),that can fit next to a desk or on a desktop or can be carried around.They either are stand-alone machines or are connected to a computer network,such as a local area network.A local area network (LAN) connects, usually by special cable, a group of desktop PCs and other devices, such as printers, in an office or a building. Microcomputers are of several types: desktop PCs, tower PCs, notebooks (laptops), mobile internet devices (MIDs), and personal digital assistants— handheld computers or palmtops. DESKTOP PCs Desktop PCs are older microcomputers whose case or main housing sits on a desk, with keyboard in front and monitor (screen) often on top. Small. 

                        The Mac Mini has the smallest desktop microcomputer case, just 6.5 inches square and 2 inches tall.

Tower PCs are microcomputers whose case sits as a “tower,” often on the floor beside a desk, thus freeing up desk surface space. Some desktop computers, such as Apple’s iMac, no longer have a boxy housing; most of the computer components are built into the back of the flat-panel display screen.
Notebook computers, also called laptop computers, are lightweight portable computers with built-in monitor, keyboard, hard-disk drive, CD/DVD drive, battery, and AC adapter that can be plugged into an electrical outlet; they weigh anywhere from 1.8 to 9 pounds.
A new category of mobile devices, smaller than notebook computers but larger and more powerful than PDAs (see below), mobile internet devices (MIDs) are for consumers and business professionals. Fully internet integrated, they are highly compatible with desktop microcomputers and laptops. The initial models focus on data communication, not voice communication.
Personal digital assistants (PDAs), also called handheld computers or palmtops, combine personal organization tools— schedule planners, address books, to-do lists—with the ability in some cases to send email and faxes. Some PDAs have touch-sensitive screens. Some also connect to desktop computers for sending or receiving information.

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