Output devices are the opposite of input devices. They are devices which recieve information from the computer and output it in to a format that is usable by a person or another device.

Examples of output devices are:

Some devices are seen as both input and output devices by some exam boards. For example, a USB Memory Stick, while not fitting in with the traditional definition of an input or an output device, both gives data and receives is and so is seen as both sometimes.

The 2014/2015 IGCSE Computer Science specification requires that you also understand:

1) How some output devices work

2) How they are used in real life scenarios

The devices you need to know about are shown below.


LCD displays were once the most common type of flat screen monitor before the LED came along. The display works in the same way as polarising sunglasses. When the liquid crystals are put one in front of the other (with one turned at 90 degrees to the first) they don’t let light in. When they are turned to the same direction light is allowed through. LCD screens use this technology and add a ‘twisted’ crystal in to the mix. When electricity is not going through the twisted crystal the light is allowed through. When electricity is passed through it blocks the light. Lots of these crystals are put together to form pixels and show the image that you see. Light is passed through the crystals using a CCFL tube (cold-cathode fluorescent lamp)



LED screens are effectively the same technology as LCD in the way that they block and allow light through. The difference is that LED screens use a light-emitting diode to send the light through the panel and to you instead of a CCFL tube. A light emitting diode is a semi-conductor which emits light when electricity is passed through it. They still contain the same crystals to allow through of block the light.




OLED stands for Organic Light Emitting Diode. As of 2016 it is a relatively new technology. It works in the same way as LED in that it uses liht emitting duides to send out light to the panel which make up the picture. The difference is that there are no crystals needed this time. This is because the organic LEDs are so small that we can have one per pixel. This means a couple of things. Firstly we can have perfect blacks on an OLED screen because we can just switch off the individual LEDs. Secondly, because we no longer need the crystals, and the LEDs are so small, we can make the TVs very thin and even make them curve.

A digital light projector uses digital micro-mirrors to reflect the light from the lamp and through the lens. They use LCD technology to create the image and just differ in how they send the image on to the screen or board.
LCD projectors use the same LCD technology as DLP projectors apart from that they use 3 layers of glass panel to reflect the light.

An inkjet printer passes a cartridge (or two cartridges if it contains both black and colour ink) over the paper, dropping tiny droplets of ink as it goes back and forth. Where the ink is dropped depends on the data received from the computer to the printer. As the cartridges do one pass over the paper, the paper is moved slightly forward to allow the next line of droplets to be placed. This continues until a representation of the digital image has been produced.

Instead of the ink in an inkjet printer, a laser printer uses what is called ‘toner’. This is a carbon passed powdered form of ink. As a laser beam scans back and forth across a ‘drum’ in the printer, static electricity is built up which draws the powdered ‘toner’ on to the paper.


A 3d printer works in the same way as an inkjet printer, with a cartridge moving across the top. The cartridge however contains a different material which can be both solid and liquid depending on temperature (such as plastic). A shape is sent to the printer from the computer software. The liquid form of the material is dropped in layers on to the base of the printer over and over again until the shape is formed. When allowed to dry the shape becomes solid.

A 2D/3D cutter is a machine which cuts materials based on what a user has specified using a computer program. It works in the same way as a 3D printer, in that it uses the model created on the computer to follow the X and Y coordinates but instead of creating a shape it uses a sharp implement to cut plastics and even metals in to shapes.

Computer speakers take a digital representation of a sound and transfer it in to something which can be heard. They produce an electronic signal to a cone inside the speaker to move. The movements of the cone affect the air in front of the speaker creating sound waves.

Headphones work in the same way as speakers except they have a protective padding around the speaker to insulate the sound and keep it from being heard by anyone but the user

1) Explain how headphones transfer digital in to analogue sound.

2) The printer runs out of paper during the printing job. A signal is sent back to the computer to stop temporarily its current task. Name this type of signal.