Computer Defination to Key Terms


A computer is a machine that can be programmed to accept data (input) process it into useful information (output) and store it away (in a secondary storage device) for safekeeping or later reuse.  The processing of input to out-put is directed by the software but performed by the hardware. To function, a computer system requires four main aspects of data handling: input, processing, output, and storage.

Central Processing Unit

The central processing unit (CPU) is a complex set of electronic circuitry that executes program instructions; it consists of a control unit and an arithmetic/logic unit. The central processing unit interacts closely with primary storage, or memory.  Memory provides temporary storage of data while the computer is executing the programme.  Secondary storage holds the data that is permanent or semi permanent. The control unit of the central processing unit coordinates execution of the program instructions by communicating with the arithmetic/logic unit and memory the parts of the system that actually execute the program. The arithmetic/logic unit (ALU) contains circuitry that executes the arithmetic and logical operations. The unit can perform four arithmetic operations: addition, subtraction, multiplication, and division. Its logical operations usually involve making comparisons that test for three conditions: the equal to condition, the less than condition, and the greater than condition. The computer can test for more than one condition at once, so it can discern three other conditions as well less than or equal to greater than  or equal to and less than or greater than,


A keyboard is a common input device that may be part of a personal computer or a terminal connected to a remote computer.  A source document is the original written data to be keyed into the computer.



A mouse is an input device with a ball on its underside, whole movement on a flat surface causes a corresponding movement of the pointer on the screen.  Moving the mouse (or pressing keyboard keys) allows you to reposition the pointer, then click the mouse button to set the insertion point, or cursor.  An icon, a pictorial symbol on a screen, can be clicked to invoke a command to the computer, a process called a graphical user interface (GUI).



The monitor features the computer’s screen, includes the housing for its electrical components, and probably sits on a stand that tilts and swivels.  Screen output is known in the computer industry as soft copy because it is intangible and temporary, unlike hard copy, produced by a printer on paper, which is tangible and can be permanent. The most common kind of computer screen is the Cathode ray tube (CRT).  Some computer screens are monochrome – the characters appear in one color, usually green or amber, on a dark background.  Most CRT screens use a technology called raster scanning, in which the backing of the screen display has a phosphorous coating, which will glow whenever it is hit by a beam of electrons.  The screen image must be refreshed often to avoid flicker.  The scan rate is the number of times the screen is refreshed per second.  Interlaced screens are scanned every other line, but non-interlaced (NI) screens are preferred for animated graphics. 

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