Input and Output Devices
This chapter addresses the issue of interaction of humans and the environment with the computersystem. If you need to acquire a comprehensive knowledge about interaction with computers, like
most areas in computer systems you need to have hands on experience in handling these
components.
Input Devices
Input devices refer to any device that can provide an input of information, data or commands intothe computer system. In a situation where we consider the CPU as the brain of the computer, the
input devices act like the eyes, ears and any other sensory organ of the human body. Advance
systems may have many input devices that can replicate all the senses on the human body. For
example a humanoid robot will have all the sense of a human in addition to many more. In the
case of a primitive and simple computer system the most common input devices are the keyboard
and the mouse.
Keyboard
The keyboard is also referred to as the primary input device of the computer system. This meansthat using the keyboard you can do the simplest input functions of entering data and commands to
your computer system. The keyboard has a similar layout to the typewriter but has some
additional keys that provide additional functionality than a typewriter. Keyboards come in
different shapes and sizes but may differ in the number of additional keys.
The keyboards may be connected to the computer system through a wire or as wireless. The
wired connection may be through the DIN-5 connector, PS/2 connector or USB. The wireless
may use radio-frequency or infrared. In addition to the keyboard there is a special unit called a
dongle, which can be connected to the USB interface of the computer system. This device is used
by the computer system to communicate with the wireless keyboard.
Standard keyboard
The standard keyboard has one hundred keys. This set of keys can be divided into sixcategories.
Alphanumeric keys - These include the alphabetical and numeric keys grouped together on
the left side of the keyboard. The main function of these keys is to simply enter what ever
symbol that is displayed on the particular key. Alphanumeric keys also include the “Tab,
Caps Lock, Backspace, Enter and symbol keys".
• Modifier keys - These keys are located on the bottom left and right corners of the grouping
of the alphanumeric keys. These are the keys that modify the functionality of another key.
This implies that the functionality of a particular key if pressed alone is different from the
functionality if pressed with a modifier key. These keys include “Shift, Ctr l and Alt". For
example “Ctr l + S" does the saving of a file and “Alt + F" will display the file menu of
your application.
• Numeric keypad - These are the set of keys that are located at the right most end of your
keyboard. As the term implies the numeric keypad comprises of number keys from 0 to 9
and mathematical operator, numloc, enter and decimal keys. These help to enter numeric
data faster that using the alphanumeric keys.
• Function keys - these are the keys located on the top most row of the keyboard and a
labeled F1 to F12. These keys are allocated certain functions by different application. For
example most applications allocate the function of showing the “application help" to the
F1 key.
• Cursor-Movement keys - These are the keys that are usually located between the
alphanumeric and number pad keys. These cursor keys include the quad-directional arrows
keys and the “Home, End, Page-up, Page-down" keys are the movement keys.
• Special-purpose keys - These keys are special keys usually located between the
alphanumeric and number pad keys which allow you to carryout special functions. These
keys are the “Insert (also known as the overwrite), Delete, Print screen, Scroll Lock, Pause
and Es c"
• Listed below are some of the functionality of a set of selected keys:
• Caps Lock - All alphabetical character you type will be in capitals
• Num Lock - When is on the number pad will enter numbers when pressed, else it will
function as the cursor-movement keys and special keys printed on them
Es c - Exit of escape from a task
• Delete (Del) - Delete a file or the character on the cursor’s right.
• Insert (Ins) - Overwrite the character on the cursor’s right when Insert is On.
• Home - The cursor goes to the leftmost end
• End - The cursor goes to the rightmost end
• Page-up - Goes to the previous page
• Page-down - Goes to the next page
• Print Screen (PrtScrn) - Take a screen shot of the screen
• Pause/Break - Mainly used to pause and debug programs
• Scroll Lock - Effects the movement of the cursor on scroll lock supporting programs.
When On the cursor will be in the same location relative to the screen but the displayed
file will move according to the arrow keys.
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