Output Devices

Output Devices: Information for the User

Output devices provide the results after processing, in a suitable form. In many cases this will be in the form of a hard copy (printout), or on screen (soft copy). With the widespread use of electronic mail (e-mail), output could be in the form of an electronic message to another computer.

Display Screens (Monitors)

Today the computer monitor is the most common form of output, which is also referred to as the VDU or Visual Display Unit that is the most prolific form of output.

Pixel is the name given to a picture element and refers to the smallest area of the screen. The entire screen is made of a lot of pixels. The clarity or clearness of a computer screen is measured in terms of resolution. Screens are normally classed as low resolution, medium resolution or high resolution. High-resolution monitors use more pixels than low resolution.

The quality of a computer monitor is based on the following properties:

• The resolution
• The number of possible colors
• The size (normally the monitors come in sizes of 15" and 17")
• Energy consumption and radiation

Different types of display screens:

Standard television set - An ordinary home television can be used for computer output.

Standard computer monitors - These have better resolution than TV monitors. Larger monitors with high resolution are used for specialized applications such as Desktop Publishing and CAD.

Liquid Crystal Displays - These are screens made up of two glass plates with liquid in between.

Printers

There are many types of different printers used for computer output. We will consider 3 types in this section.

• Dot-matrix printers
• Ink-jet printers
• Laser printers

Dot-Matrix Printers

Dot-matrix printers are impact printers, which can transfer print through layers of paper. This means that they are able to print multi-part stationery.

Example:

If you want to print a multi-part sheet where, the white top sheet goes to the customer, the yellow sheet goes to accounts and the blue sheet to the store sheet, then you will need to use a dot-matrix printer. (similar to the blue, yellow and green layers of bills found in shops when they write the bill).

A dot-matrix printer is very cheap and has the lowest running costs of any printer. It has a matrix of small pins in its print head. As the head moves across the paper the correct pins are fired out to hit an inked ribbon and the shape of the letter required is formed. The greater the number of pins, the higher the quality of the print.

Ink-Jet Printers

An ink-jet printer is a non-impact character printer. They are silent in operation, have good quality printing and have become a very popular printer for PCs. The print head of an ink-jet printer consists of nozzles (usually 64). The ink flows through the appropriate nozzle, where it is heated and a bubble forms. This expands and breaks, releasing a very small ink droplet. These dots are much smaller, and there are more of them, than in a dot-matrix printer. These printers produce printouts that are almost comparable to that produced by laser printers and therefore can print high quality text and graphics.

Laser Printers

These are non-impact page printers. A laser beam is used to form an image on a rotating charged metal drum. Laser printers have toner cartridges, which contain a fine powder called toner. The charged image then picks up the toner particles, which are transferred to the paper, which is also charged. Once the image has been transferred, heat and pressure are used to stick it to the paper permanently.

Since they are page printers they are very fast. The speed of a laser printer is typically about 8 ppm (pages per minute). Color laser printers are now available. Laser printers offer both high speed and excellent print quality of text and graphics. Although they are expensive, they have become widespread in many offices where quality printouts are needed because of the many advantages it has.

Graph Plotters

A plotter is a device commonly used in producing printing plans, maps, line diagrams and three-dimensional drawings, which are particularly line diagrams or graphical output on paper.

Graph plotters use pens to produce images and different pens containing different colored inks may be used. Plotters are generally classified as pen plotters or as pen less plotters. Pen less plotters use various kinds of different technologies. At the moment high quality work for publication is done on electrostatic plotters.

Voice Synthesis

Voice synthesis is used when you get the output as sound. This method is usually very useful for handicapped people.

Example:

Visually handicapped people, find the spoken word from a computer invaluable. For instance, each letter as it is typed can be heard on headphones when special software with a word processor is used.

Projector

These are special devices, which can be connected to the computer and used as a substitute to the monitor. These are used when the output has to be shown to a large audience by projecting the computer output on a white screen or wall.