3.3 MONITORS

 One of the most important output devices in computer system is its screen commonly called monitor. It is an output device and displays all the programs and applications to which you are running in your computer system. Monitor is the visual display unit of the computer system. It displays images generated from the video output. Monitor of the computer system is used to display images without keeping a permanent record inside it.

Graphic display is made up of a series of dots called ‘pixels’ (picture elements) whose pattern produces images in computer system. Each dot on the screen is defined as a separate unit which can be addressed separately. Since each dot on the screen can be controlled separately by virtue of which it gives greater flexibility in drawing pictures. Number of dots per inch (dpi) is called the resolution of the screen and is used to represent the quality of the computer system. There are three categories of display screen technology:

1. Normal Cathode Ray Tube (CRT)

2. Liquid Crystal Display (LCD) / (TFT LCD)

3. Projection Displays

3.3.1 Normal Cathode Ray Tube Monitors (CRT)

Monitors display what is going on in your computer. They can run at various resolutions. It is the part of computer which looks like a TV set. After typing the characters from the keyboard we can see them on the monitor.

The main components of a CRT monitors are the electron gun, the electron beam controlled by an electromagnetic field and phosphor coated display screen. These older monitors were very bulky and acquire a lot of space for installation. 


In CRT monitors image is projected on the screen by directing the electron beam on the computer screen. To precisely direct the electron beams, copper steering coils are used to create magnetic field inside the tube. By applying varying voltage to copper coils a beam can be positioned at any point on the screen.

3.3.2 Liquid Crystal Displays (LCD)

This was first introduced in watches and clocks in 1970’s. LCDS is now used to display images in monitors. A newer technology in computer screens is TFT LCD monitors. These are light weight monitors and are used in laptop computers. 

The three main advantages of these monitors over the CRT are the use of less space on the desk, less power consumption and flicker free screen. 


These monitors are portable and consume less electricity. Images produced by these monitors are of better quality than that of old CRT monitors. The LCD monitors have very high resolution and emit less radiation than CRT monitors.

3.3.3 Projection Displays

These are normally used for large group presentations. These systems can be connected to computer and whatever appears on the computer terminal gets enlarged and projected on a large screen.


In this computers are connected to an LCD Flat screen and images are projected on a large screen by using overhead projector. These are popularly used for seminars, class rooms, marketing presentations etc.

Classification of Monitors on the basis of Color

In terms of color capabilities, monitors can be divided into following types:
1. Monochrome: These monitors display the result in two colors, i.e., black/white, green/black, amber/black. One color is for background of the screen and other for the foreground and you
may see it being used at railway reservation counters.

2. Gray Scale: It is monochrome type of the monitor, but it displays the output by using the different shades of gray, made by combination of black and white.

3. Color Monitor: It can display the output in many colors, ranging from 16 to over 1 million different colors. These are also called as RGB monitors, because they accept three separate signals, which are 
red, green and blue.

Classification of Monitors on the basis of Size

After color classification, the most important aspect of a monitor is its screen size. Size of computer screen is measured in diagonal inches and is given by measuring the distance from one corner to the opposite corner (diagonally). The smallest size for VGA monitors is 14 inches, which is also the entry level monitor for computer system. The larger size landscape monitors can display two full pages side by side at a time.

Classification of Monitors on the basis of Resolution 

The resolution of a monitor means number of pixels per inch are of the monitor. In general, the number of more pixels will be the sharper images. Most modern monitors can display 1024 by 768 pixels. Some highend models of computer monitors can display 1280 by 1024, or even 1600 by 1200 pixels.

Classification of Monitors on the basis of Signal

Computer monitor can be divided into two categories on the basis of signals to which they accept.

These are:
1. Analog Monitor,
2. Digital Monitor.

Analog Monitor:

Electronic signal that is sent by signals of varying frequency instead of sent as ON or OFF data transmission is called analog signal. Analog allows equipment to handle information that continuously changes such as voltage, current, wave etc. Analog signals can be represented by wave sign and  watches which changes there position These are traditional type of color monitors which are based on CRT technology. These work like the television screen and accept analog signals.

Digital Monitor

An electronic signal that is sent as binary digits of either ON or OFF is called Digital signal. Example given in Figure5 is of digital signals and how they look like. In the first diagram signals are either 0 or 1 i.e., up or down for ON and OFF mode. In the right digital pictures are shown where a pixel is either ON or OFF helping to create an image on the display screen.


The digital monitor receives digital signals and uses CRT technology. The data in these monitors is received from video adapter. These are of different types such as CGA (Color Graphics Adapter), EGA (Enhanced Graphics Adapter), VGA (Video Graphics Array), SVGA (Super Video Graphics Array) and are fast and produce clear images.

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