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.  In simple terms, input devices bring information INTO the computer and output  devices bring information OUT of a computer system. These input/output devices are  also known as peripherals since they surround the CPU and memory of a computer  system.  

Some commonly used Input/Output devices are listed in table below.

Input Devices 

  • Keyboard  
  • Mouse  
  • Joystick  
  • Scanner  
  • Light Pen  
  • Touch Screen
  • Microphone
  • Barcode reader
  • Camera
  • Trackballs
  • Gamepad
  • OCR
  • Magnetic tape drive
  • Graphics tablet
  •  

Output Devices

  • Printer
  • Monitor
  • Speaker
  • Projector
  • Film recorder
  • Plotter
  • Visual display unit

Input Devices


1. Keyboard  

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. 

Spacebar: 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). 

2. 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  are:

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.  

3. 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

4. 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.  

Hand-held scanners are commonly seen in big stores to scan codes and price  information for each of the items. They are also termed the bar code readers.  

5. Bar codes  

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.

6. 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.  

7. Touch Screen  

 It allows the user to operate/make selections by simply touching the display screen.  Common examples of touch screen include information kiosks, and bank ATMs.  

8. Digital camera  

A digital camera can store many more pictures than an ordinary camera. Pictures  taken using a digital camera are stored inside its memory and can be transferred to a  computer by connecting the camera to it. A digital camera takes pictures by  converting the light passing through the lens at the front into a digital image. 

9. The Speech Input Device  

The “Microphones - Speech Recognition” is a speech Input device. To operate it we  require using a microphone to talk to the computer.

Also we need to add a sound card  to the computer. The Sound card digitizes audio input into 0/1s .

A speech recognition  program can process the input and convert it into machine-recognized commands  or input. 

10. Optical Character Reader (OCR)

It is also a reading device that reads printed text by scanning it character by character. It first converts them into machine-readable code and saves them in the system memory.

11. Bar Code Readers

Again a reading device but to read barcode data like on goods, books, etc. It can be a handheld scanner or a stationary one but they both scan the image by converting it to alphanumeric value on the computer.

12. Optical Mark Reader (OMR)

It is an optical scanner to recognize marks by pen and pencil and is commonly present in educational institutions to check objective exam papers.

Output Devices  


1. Monitor  

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.  

2. Liquid Crystal Display (LCD) 

LCD was introduced in the 1970s and is now applied to display terminals also. Its  advantages like low energy consumption, smaller and lighter have paved its way for  usage in portable computers (laptops).  

3. Printer  

Printers are used to produce paper (commonly known as hardcopy) output. Based on  the technology used, they can be classified as Impact or Non-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.  

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

When we talk about printers we refer to two basic qualities associated with printers:  resolution, and speed. Print resolution is measured in terms of number of dots per  inch (dpi). Print speed is measured in terms of number of characters printed in a unit  of time and is represented as characters-per-second (cps), lines-per-minute (lpm), or  pages-per-minute (ppm).

4. Speakers

An output device that produces sound after receiving a command from the computer. They support the computers as well as other hardware devices. Now we also have wireless speakers with Bluetooth technology. 

5. Projector

This is an optical device that presents visuals on the screen, stationary and moving both. They are present at movie theatres, auditoriums, etc. It connects to the computer and displays the image on it on a larger screen.

6. Plotter

It is a device to make graphics, prints and other vector images to give a real life illustration vibe. It is mandatory to have a graphic card to use the device. The pen like device that comes with it helps in replicating the exact design on the computer.

7. Braille Reader

Made for the blind users, this device is to process computer data in braille format. It allows users with low or no vision to recognize the data as the braille reader put data on the paper in embossed format. They can run their fingers over it to understand everything easily.

8. Television

A very common output device present in most of the households is a display output device. It portrays video and audio files on the screen according to the user’s needs. Before we had CRT screens but now most of us use plasma displays.

9. Video Card

This device goes inside the sockets of a motherboard of the computer system. It improvises the digital content appearance in other output devices. It is very important now with many people having multiple devices just for personal use.

10. Global Positioning System

A device to help users with directions, GPS uses satellite technology to track geographical location of the users. There is a continuous latitudinal and longitudinal calculation to have an accurate result every time. Most of the vehicles and smart devices have GPS as an inbuilt feature.

11. Headphones

Similar to speakers, this device has a lower sound frequency. They can’t be easily heard in large areas like grounds and parks but are only accessible to a single person using the device. A headset is another name for them.

Both Input and Output Devices of Computer


There are many devices that have characteristics of both input and output devices. They can receive data as well as give out a result becoming useful for both purposes.

Some of them are – 

1. USB Drive – It is a detachable device which can receive data from any computer as well as send out data to other devices. 

2. Modems – It is responsible for transmitting data from one device to another using telephonic lines. 

3. CD and DVD Drives – Saves data from the computer in the given format and can also send out data to other devices with disk space. 

4. Headset – It has a speaker which is an output device and a microphone which is an input device. 

5. Facsimile – This is a fax machine with scanner being an input device and printer being the output device. 

Difference between Input Devices and Output Devices


INPUT DEVICE OUTPUT DEVICE
Accepts user data Reflects user data
The user commands them Processor commands them
Conversion of friendly instruction into a machine friendly Conversion of machine’s instructions to user needs
Sends data to the processor for execution Sends processed data back to the user.
Helps computer in receiving data Helps computer in displaying data
Complex design structure Less complex design structure 
Example – Keyboard, Image Scanner, etc. Ex: Monitor, Printers, etc.