a computer is a machine that can be programmed to accept data process data into useful information and store it for later use. a computer consists of hardware and software. the machine is know as hardware. the programs are called software. the processing of input to output is directed by the software but performed by the hardware.
A computer system requires different components to perform the function of Input processing, output and storage. these components are as follows:
1. input devices
The data that is given to the computer is called input. input devices are used to input data and instructions into the computer. these devices are keyboard and mouse.
secondary storage
secondary storage devices
input devices
send data to stores data and programs output
CPU executes computer devices make
instruction processed
data
memory holds data and (information)
programs currently in use available
Input Processing Output
2. processing device
the processor is used to process data. it is also called central processing unit (CPU). it is the brain of the computer. it consists of electronic circuit. CPU interprets and executes program instruction. all computers must have a central processing unit.
main memory is used to store the input data before processing. it also stores processed data after processing until the data is sent to the output device. the main memory is closely connected to CPU but it is separate from it
the data processed into useful information is called output. output devices are used to display the result of processing. the most common output devices are monitor and printer.
4. storage devices
storage usually refers to the secondary storage. the main memory stores data and programs temporarily. the secondary storage is required to store data, information and programs permanently. the most common storage devices are floppy disk hard disk drive and CD ROM etc.
keyboard
Keyboard is the most commonly used input device data is mostly entered using a keyboard the buttons on the keyboard are called keys. A standard keyboard contains over 100 keys. A keyboard contains numeric keys alphabetic keys function keys and special-purpose keys.
a standard keyboard is normally called QWERTY keyboard. this is because the first six keys on the top row of letters on these keyboards are Q,W,E,R,T,Y.
main parts of keyboard
The keyboard in most personal computers have the following main parts:
1. function keys 2. main keyboard (in the center)
3. numeric keys (to the right) 4. additional keys
1. Function keys
function keys from f1 to f12 are used to perform special functions. Their function depend on the software being used in the computer.
2. Main keyboard
the main keyboard includes the keys found on a type writer keypad. it also contains some special keys the special keys have different uses and effects that depend on the software being used.
101-key enhanced keyboard
101- key enhanced keyboard has some additional keys between the main keypad and the numeric keys. it also contains status lights in upper-right corner.
a) Escape key
Escape key is used to terminate a command or current task.
b) Caps Lock key
caps lock key is a toggle key. the characters appears in uppercase if it is pressed. The characters appear in lowercase if it is not pressed. Numbers and symbols are not affected. the status light under "Caps Lock" turns on when it is pressed.
c) Tab key
tab key is used to move the cursor to next tab stop.
d) shift keys
shift key is pressed in combination with other keys to produce upper case letters and the upper symbols shown on certain keys.
e) Control keys
control key is pressed in combination with other keys to execute commands. for example, Ctrl O is used to open a new file.
f) Alt keys
ALT key is also used in combination with other keys to execute commands.
g) Backspace
Backspace key is used to delete single character on the left of the cursor.
h0 Enter key
enter key is used to move the cursor to the bigning of the next line. it is normally used at the end of a paragraph.
3. Numeric keys
numeric keys are located on the right side of most keyboards. The numeric keys are used for two purposes depending on the status of num lock key. if num lock is on, the key are used to enter numeric data and mathematical symbols like +,-,*,/. if num lock key is off, the numeric keys are used to move the cursor and perform other functions as follows:
Keys Description
1
End it is used to move the cursor to the right corner of screen.
2
Down it moves the cursor down one line.
3
pg no it is used to move the cursor one page down on the screen.
4
Lt it moves the cursor one character to the left.
6 it moves the character to the right.
Rt
7
Home it is normally used in word processing or text editors to move the cursor to the top of the screen.
8
Up it moves the cursor one line up.
9
Pg up it is used to move the cursor one page up on the screen.
0
Ins it is used to switch between insert Mode and Over type Mode. it is a toggle key.
Del it deletes characters to the right of cursor. it is also used to delete files.
4. Additional keys
Some additional keys on extended keyboard are as follows:
1. Arrow keys: the arrow keys are used to move the cursor position.
2. Insert, Delete, Home, End, Page up and Page Down keys: These keys are above the arrows key. the functions of these keys are same as numeric keys 0, decimal point (Del), 7,1,9 and 3.
3. print screen: it is used to take a snap of the computers screen.
4. scroll Lock: it locks and unlocks the cursor on screen in some programs. the cursor moves normally when it is turned off. it does not work in all programs .
5. pause or Break key: it is used to pause screen when information is too fast to read.
