Input Devices & Output Devices

The computer will be of no use unless it is able to communicate with the outside world. Input/Output devices are required for users to communicate with the computer.

1. Input Devices:-

Input devices that enter the information in to the computer.
(or)
Input devices bring information into the computer.

Examples:
A) Key Board:-

It is a text base input device that allows the user to input alphabets, numbers and other characters. It consists of a set of keys mounted on a board.

Alphanumeric Keypad:

It consists of keys for English alphabets, 0 to 9 numbers, and special characters like + − / * ( ) etc.

Function Keys:

There are twelve function keys labeled F1, F2, F3… F12. The functions assigned to these keys differ from one software package to another. These keys are also user programmable keys.

Special-function Keys:

These keys have special functions assigned to them and can be used only for those specific purposes. Functions of some of the important keys are defined below.

Enter:

It is similar to the ‘return’ key of the typewriter and is used to execute a command or program.

Space bar:

It is used to enter a space at the current cursor location.

Backspace:

This key is used to move the cursor one position to the left and also delete the character in that position.

Delete:

It is used to delete the character at the cursor position.

Insert:

Insert key is used to toggle between insert and overwrite mode during data entry.

Shift:

This key is used to type capital letters when pressed along with an alphabet key. Also used to type the special characters located on the upper-side of a key that has two characters defined on the same key.

Caps Lock:

Cap Lock is used to toggle between the capital lock features. When ‘on’, it locks the alphanumeric keypad for capital letters input only.

Tab:

Tab is used to move the cursor to the next tab position defined in the document. Also, it is used to insert indentation into a document.

Ctrl:

Control key is used in conjunction with other keys to provide additional functionality on the keyboard.

Alt:

Also like the control key, Alt key is always used in combination with other keys to perform specific tasks.

Esc:

This key is usually used to negate a command. Also used to cancel or abort executing programs.

Numeric Keypad:

Numeric keypad is located on the right side of the keyboard and consists of keys having numbers (0 to 9) and mathematical operators (+ − * /) defined on them. This keypad is provided to support quick entry for numeric data.

Cursor Movement Keys:

These are arrow keys and are used to move the cursor in the direction indicated by the arrow (up, down, left, right).

B) Mouse:-

The mouse is a small device used to point to a particular place on the screen and select in order to perform one or more actions. It can be used to select menu commands, size windows, start programs etc.

The most conventional kind of mouse has two buttons on top: the left one being used most frequently.

Mouse Actions:-

Left Click : 

Used to select an item.

Double Click : 

Used to start a program or open a file.

Right Click : 

Usually used to display a set of commands.

Drag and Drop: 

It allows you to select and move an item from one location to another. To achieve this place the cursor over an item on the screen, click the left. mouse button and while holding the button down move the cursor to where you want to place the item, and then release it.

C) Joystick:-

The joystick is a vertical stick which moves the graphic cursor in a direction the stick is moved. It typically has a button on top that is used to select the option pointed by the cursor. Joystick is used as an input device primarily used with video games, training simulators and controlling robots

D) Scanner :-

Scanner is an input device used for direct data entry from the source document into the computer system. It converts the document image into digital form so that it can be fed into the computer. Capturing information like this reduces the possibility of errors typically experienced during large data entry.

E) Bar Code Reader :-

A bar code is a set of lines of different thicknesses that represent a number. Bar Code Readers are used to input data from bar codes. Most products in shops have bar codes on them.Bar code readers work by shining a beam of light on the lines that make up the bar code and detecting the amount of light that is reflected back.

F) Light Pen:-

It is a pen shaped device used to select objects on a display screen. It is quite like the mouse (in its functionality) but uses a light pen to move the pointer and select any object on the screen by pointing to the object.

Users of Computer Aided Design (CAD) applications commonly use the light pens to directly draw on screen.

G) Track ball :-

It is used to operate the Laptops instead of Mouse.

Other Input Devices

Output Devices:-
Output devices bring information OUT of a computer system.
(or)
The data that come out from the computer.

Examples:-

A) Monitors:

Monitor is an output device that resembles the television screen and uses a Cathode Ray Tube (CRT) to display information. The monitor is associated with a keyboard for manual input of characters and displays the information as it is keyed in. It also displays the program or application output. Like the television, monitors are also available in different sizes.

Types of Computer Monitors:

Most people use computer monitors daily at work and at home. And while these come in a variety of shapes, designs, and colours, they can also be broadly categorized into three types.

I. CRT (Cathode ray tube) monitors:-

These monitors employ CRT technology, which was used most commonly in the manufacturing of television screens. With these monitors, a stream of intense high energy electrons is used to form images on a fluorescent screen. A cathode ray tube is basically a vacuum tube containing an electron gun at one end and a fluorescent screen at another end.

II. LCD (liquid crystal display) monitors:-

The LCD monitor incorporates one of the most advanced technologies available today. Typically, it consists of a layer of colour or monochrome pixels arranged schematically between a couple of transparent electrodes and two polarizing filters. Optical effect is made possible by polarizing the light in varied amounts and making it pass through the liquid crystal layer.

III. LED (light-emitting diodes) monitors:-

LED monitors are the latest types of monitors on the market today. These are flat panel, or slightly curved displays which make use of light-emitting diodes for back-lighting, instead of cold cathode fluorescent (CCFL) back-lighting used in LCDs. LED monitors are said to use much lesser power than CRT and LCD and are considered far more environmentally friendly.

B) Printers:-

Printers are used to produce paper output. Based on the technology used, they can be classified as Impact or Non-impact printers.

I. Impact Printers:

Impact printers use the typewriting printing mechanism wherein a hammer strikes the paper through a ribbon in order to produce output. Dot-matrix and Character printers fall under this category.

II. Non-Impact Printers:

Non-impact printers do not touch the paper while printing. They use chemical, heat or electrical signals to etch the symbols on paper. Inkjet, Desk jet, Laser, Thermal printers fall under this category of printers.

Classification of printers:
· Character printers
· Line printers
· Page printers

Dot-matrix printers:

These printers print each character as a sample of dots. The print head comprises a matrix of tiny needles, typically seven rows with nine needles in each (9 ´ 7 matrix). Printing quality of this printer is not good and speed of this printer is also very slow. The quality and price of dot-matrix printer depends on two factors.

i) Number of dots per inch termed as DPI

ii) Number of characters or words per minute

100 – 150 DPI

200 – 300 Character per minute

40 – 80 Words per minute

Laser Printers:

These are very high speed non impact printers which produce documents at speeds of over 20,000 lines per minute. This type of printers use a special beam of light called LASER. Where Laser stands for Light amplification by Simulated Emission of Radiation. With LASER, magnetic material in shape of powder is thrown on paper in the form of microscopic dots. The quality and cost of LASER printer depends on two factors:

· Number of dots per inch (DPI)

· Number of pages per minute

There are three qualities of a LASER printer:

Cheapest Quality Laser printer:
This type of laser printer can print
600 DPI
5 – 10 Pages per minute

Middle quality LASER:
This type of LASER can print
300 – 1200 DPI
10 – 20 Pages per minute

High quality LASER:
This type of LASER can print:
600 – 1200 DPI
30 – 300 Pages per minute

C) Speakers:-

Speaker are another types of output device, which allow you to listen to voice like music, and conversation with people.

D) Projector:-

Projector is also an output device.
It is used to show presentations. There two main types of projector.

1. Simple Projector
2. Multimedia projector.

E) Plotter :-

A plotter is a special kind of output device that , like a printer produces image on paper but does so in a different way. Plotters are designed to produce large drawings or image, such as construction plan for building or blueprints for mechanical object. A plotter can be connected to the port normally used by a printer.

There are two types of designs:
1) Flat bed: 

Plotters of small size to be kept on table with restriction of paper size.

2) Drum: 

These plotter are of big size using rolls of paper of unlimited length.

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