Central processing unit (CPU) — The part of the computer that executes program instructions is known as the processor or central processing unit (CPU). In a microcomputer, the CPU is on a single electronic component, the microprocessor chip, within the system unit or system cabinet. The system unit also includes circuit boards, memory chips, ports and other components. A microcomputer system cabinet will also house disk drives, hard disks, etc., but these are considered separate from the CPU. This is principal part of any digital computer system, generally composed of control unit, and arithmetic-logic unit the ‘heart” of the computer. It constitutes the physical heart of the entire computer system; to it is linked various peripheral equipment, including input/output devices and auxiliary storage units
o Control Unit is the part of a CPU or other device that directs its operation. The control unit tells the rest of the computer system how to carry out a program’s instructions. It directs the movement of electronic signals between memory—which temporarily holds data, instructions and processed information—and the ALU. It also directs these control signals between the CPU and input/output devices. The control unit is the circuitry that controls the flow of information through the processor, and coordinates the activities of the other units within it. In a way, it is the "brain", as it controls what happens inside the processor, which in turn controls the rest of the PC.
o Arithmetic-Logic Unit usually called the ALU is a digital circuit that performs two types of operations— arithmetic and logical. Arithmetic operations are the fundamental mathematical operations consisting of addition, subtraction, multiplication and division. Logical operations consist of comparisons. That is, two pieces of data are compared to see whether one is equal to, less than, or greater than the other. The ALU is a fundamental building block of the central processing unit of a computer.
Memory — Memory enables a computer to store, at least temporarily, data and programs. Memory—also known as the primary storage or main memory—is a part of the microcomputer that holds data for processing, instructions for processing the data (the program) and information (processed data). Part of the contents of the memory is held only temporarily, that is, it is stored only as long as the microcomputer is turned on. When you turn the machine off, the contents are lost. The capacity of the memory to hold data and program instructions varies in different computers. The original IBM PC could hold approximately 6,40,000 characters of data or instructions only. But modern microcomputers can hold millions, even billions of characters in their memory.
Input device — An input device is usually a keyboard or mouse, the input device is the conduit through which data and instructions enter a computer. A personal computer would be useless if you could not interact with it because the machine could not receive instructions or deliver the results of its work. Input devices accept data and instructions from the user or from another computer system (such as a computer on the Internet). Output devices return processed data to the user or to another computer system.
The most common input device is the keyboard, which accepts letters, numbers, and commands from the user. Another important type of input device is the mouse, which lets you select options from on-screen menus. You use a mouse by moving it across a flat surface and pressing its buttons..
A variety of other input devices work with personal computers, too:
The trackball and touchpad are variations of the mouse and enable you to draw or point on the screen.
The joystick is a swiveling lever mounted on a stationary base that is well suited for playing video games.
A scanner can copy a printed page of text or a graphic into the computer’s memory, freeing you from creating
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11:49 AM on October 29, 2008
