Visual Display Units (Monitors)

Visual Display Units (VDU), or monitors, are used to visually interface with the computer and are similar in appearance to a television. Visual Display Units display images and text which are made up of small blocks of colored light called pixels. The resolution of the screen improves as the number of pixels increases. Most monitors have a 4:3 width to height ratio.

Monitors use video adapters that are part of the internal hardware in a computer. The two types of monitors are Cathode Ray Tube (CRT) monitors and flat-panel Liquid Crystal Displays (LCD). LCD's have small transistors embedded in the screen; one transistor for each cell or pixel on the screen.

Printers

You can print out information that is in the computer onto paper. By printing you create what is known as a hard copy. There are different kinds of printers which vary in their speed and print quality. The two main types of printers are impact and non-impact. The main categories of printers are: laser printers, ink-jets, dot-matrix, and multifunctional. Typically, home computer users will use ink-jets as they are relatively cheap but superior in quality to dot-matrix. Laser jets and other printers created by new technology are more expensive.

Inkjet Printer

Ink-jet (bubble-jet) printers spray ionized tiny drops of ink onto a page to create an image. This is achieved by using magnetized plates which direct the ink's path onto the paper in the desired pattern. Almost all ink-jets can print in color, but they vary in their print resolutions (i.e print quality). Some ink-jet printers are capable of producing high quality prints which almost match the quality of a laser printer. A standard ink-jet printer has a resolution of 300 dots per inch, although newer models have improved on that.

Laser Printer

Laser printers operate by shining a laser beam to produce an image on a drum. The drum is then rolled through a pool, or reservoir of ink, and the electrically charged portions of the drum pick up ink. Finally, using a combination of heat and pressure, the ink on the drum is transferred onto the page. Laser printers print quickly, and the ink supply cartridges last a long time. Color laser printers use the same toner-based printing process as black and white (B/W) laser printers except that they combine four different ink colors.

Dotmatrix Printer

Impact (dot-matrix) printers use a set of closely spaced pins and a ribbon to print letters or other characters on a page. These printers actually impact the page to print a character, much like a typewriter. Dot-matrix printers vary in terms of speed and the number of pins they have. They can run at speeds between 50 and 500 CPS (Characters Per Second). The number of pins, which can vary between 9 and 24, determines the quality of the print job. Dot matrix printers are commonly used for printing invoices, purchase orders, shipping forms, labels, and other multi-part forms.

A fax machine uses a thermal printer

Thermal Printer

Characters are formed by heated elements being placed in contact with special heat- sensitive paper to form darkened dots when the elements reach a critical temperature. Thermal printer paper tends to darken over time due to exposure to sunlight and heat. The standard of print produced is poor. Thermal printers are widely used in battery powered equipment such as portable calculators.