Output devices
Output devices are peripheral devices that a computer uses to give out information produced after the processing operations. There are two types of output devices namely the softcopy and the hardcopy output devices. Softcopy refers to intangible output mainly displayed on the screen or through other output devices such as speakers. A hardcopy is a tangible output produced mostly on papers by devices such as printers.

Softcopy output devices.
Some of the softcopy output devices are;
Monitors
A monitor or a video display unit(VDU) is the most common output device. It displays information on its screen thus helping the user to monitor operations carried out by the computer.

For a long time, monitors have been designed using a long tube called the cathode ray tube(CRT) that emits light. The screen of a cathode ray tube is curved slightly outward forming a convex shape.However,new flat displays have come which do not use CRT technology. Flat display are more comfortable to use, portable and do not consume a lot of power compared to CRT.

The figures below shows a CRT monitor and flat-panel display monitor.

                     

The sharpness or clarity of an image on the screen depends on the type of monitor being used.Monitors that display sharp clear images are said to have high resolution.The images on the screen are formed by small dots called picture elements(pixels).
The higher the number of pixels per square centimeter the higher the resolution hence the clarity.

There are two types of monitors namely monochrome and color monitors. Monochrome monitors display images and text in only one color mostly black and white.Color monitors can display images and text in multiple colors. For a monitor to display information it must be connected to a separate piece of circuit board,plugged into the motherboard called the video card or graphics adapter.However,some motherboards have on-board video capability therefore there is no need fora video card.

Examples of graphic adapters are:
Monochrome display adapter (MDA):This was the first video card that was used in early computers. MDA displayed text only in one color.
Hercules graphics card (HGC) :One weakness of the original MDA display was that,could not support images of any kind. Hercule graphic card supports monochrome images in addition to text.

Color graphics adapter (CGA):This can display text and images using up to 16 colors.
Enhanced graphics adapter (EGA):This is an improvement over color graphic adapter but also displayed text and images using 16 colors.
Video graphics array(VGA):This offers at most 256 colors.
Super video graphics array (SVGA):This is an enhancement of video graphic array capabilities offering over 256 colors.

Small portable laptops,notebooks and even desktop PCs use flat-panel display.
Common types of this display are:

Liquid crystal display(LCD):Liquid crystal displays do not display by emitting light of their own.Instead they have tiny liquid crystals that reflect light falling on them from the environment. Liquid crystal displays are widely used in watches,calculators,cell
phones and digital cameras.
Electro-luminescent(EL):These displays are an improvement on LCDs .Electro luminescent emits light when electrically charged.This makes them clear,sharper and easier to read.
Gas-plasma Display(GPD):These use a gas that emits light in the presence of electric current.
Thin film transistor(TFT):This is the latest technological advancement in displays. provides high quality output than all the others.

Sound output
Speakers are used to output sound from a computer. Sound may be inform of music, warning,video,interactive communication with a computer etc.

Light-emitting diodes(LED)

These are light emitting components that display light when an electric current is passed through them. A good example is the red or green light displayed by the system unit to help the user know whether it is on or off. Mostly LEDs are used to give warnings the same way a motorist would use signals to indicate when he/she is overtaking or taking a turn.
LCD projectors project the output from the computer to a whiteboard or wall.

Hardcopy output devices
The most common hardcopy output devices are printers and plotters.

Printers
Printers produce a hardcopy of information on papers. The quality of the hardcopy depends on the printers printing mechanism. There are two types of printers namely impact and non-impact printers.

Impact printers
The mechanism of impact printers is almost similar to that of an ordinary typewriter i.e.they produce characters by using special light hammers with characters or pins held on the printing head.To print,a paper is placed behind an ink ribbon.When the hammer strikes on the head,character mark is stamped.These printers are noisy and are mostly used to produce rough copies.The two widely used impact printers are dot matrix and daisy-wheel printers.

Dot matrix printers produce a hard copy by arranging patterns of dots on the paper using pins held in the printing head.

Figure (a) below shows an example of an impact printer.Figure (b) shows print characters formed by a dot matrix printer

    

A daisy-wheel printer has a wheel with petals on which characters are mounted. It is so called because it resembles a daisy lower.When printing,the wheel rotates allowing the petals to hit a ribbon with different characters as they are received from
the computer.

Non-impact printers
These printers do not use the striking mechanism to produce characters on a piece of paper.They do not hammer the ribbon hence they are much quieter. The major non-impact printers are inkjet,thermal transfer and laser printers.

Inkjet printers
Inkjet printers form characters by spraying ink from tiny nozzles through an electrical field that arranges the charged ink particles into characters .Inkjets are cheap to buy but expensive to run because of the high cost of ink cartridges.

Thermal printers
Thermal printers use heat to transfer characters on to a piece of paper i.e.they bond characters onto a piece of paper by using hot pins which presses against a special ribbon.They are inexpensive alternative to inkjets.

Laser printers
Laser printers prints by passing a laser beam back and forth over  a rotating drum.The laser beam draws the image on the drum by static electricity.The charged areas pick up the ink toner from the cartridge ,and press it on to the paper.Although these printers are more expensive to buy,they are faster,and cheaper to run than the inkjets.

Plotters
A plotter resembles a printer but specializes in producing big charts such as maps,pictures and drawings.They are mostly used for printing geographical,architectural and engineering drawings e.g.maps,advertisement posters to be placed on billboards,machine parts etc.