Monitor- Output Device

A monitor is a television like device used to display data or information. It is a soft copy output terminal. The quality of monitor is judged in terms of resolution. Resolution is the measure of total number of horizontal and vertical pixels that a monitor can display. A pixel is the smallest dot the computer can control on the screen.  The more pixel the computer can control higher the resolution and more detail the monitor can display.

A video display or monitor consists of a luminescent display device such as a cathode ray tube (CRT) or a liquid crystal display and controlling circuitry.

Cathode Ray Tube (CRT) Technology

The main element in a CRT monitor is the Cathode Ray Tube (CRT). A CRT is a partially evacuated glass tube, which is filled with an inert gas at very low pressure. The cathode (a negatively charged electrode, also called an 'electron gun') beams a stream of electrons towards a positively charged electrode - the screen. When the electrons touch the phosphor compounds, the kinetic energy of the electrons is converted into visible light and the coating glows to produce the picture or characters. The CRT screen is capable of displaying 80 characters of data horizontally and 25 lines vertically. The CRT screen can be classified into two types in terms of color capabilities:   

Monochrome: Monochrome monitors actually display two colors, one for the background and the other for the foreground. The colors can be black and white, green and black, or amber and black.

Color: Color monitors can display anywhere from 16 to over 1 million different colors. Color monitors are sometimes called RGB monitors because they accept three separate signals- red, green and blue (RGB).

Liquid Crystals Display

LCD consists of two polarizing filters with grooves on them. The grooves on the plates are aligned at 90 degrees to each other. When polarized light passes through the vertical groove, it is twisted at 90 degrees by the crystals, so that it is now on a horizontal plane and can pass through the horizontal grooves of the other polarizing filter. When electric current is passed through the crystals, they align themselves in the direction of light and let the vertical light-phase pass through untwisted, which is blocked by the second horizontal filter. Thus, the absence of light is seen as characters on the screen. This means that light passes through when voltage is absent and is blocked when voltage is applied to the crystal.