Monday, February 26, 2001		On Hardware

The face of your computer
By Jasjot Singh

A monitor is a display screen on which visual output (text or graphical) is created from a CPU (computer processing unit) through a video card.

It is the first thing that meets the computer user’s eye. Whatever be the processor speed or RAM capacity, processed data is not presentable without a proper monitor. It is thus, more or less, the face (or the mask!) of a CPU.

A buyer, more often than not, does not compromise on the quality of the motherboard, CPU or RAM but while purchasing a monitor, he tries to negotiate with the budget in his mind. Later, he repents after ending up with a monitor that is physically small or which doesn’t support the high resolution or refresh rate.

A substandard monitor can affect the usability of an otherwise good computer because a monitor that strains the eyes can make a computer difficult to use. They thus bear a substantial effect on the usability of the computer.

Quality comes with a cost, however. A good quality monitor, though is a bit heavy on the pocket, doesn’t get obsolete as quickly as other computer hardware like hard disks, CPU or motherboards. The investment on a monitor is long lasting.

While purchasing a monitor, the buyer should know what makes his purchase a better bet.

Monitors can broadly be categorised as:

1) Monochrome — These display two colours only viz. black and white, amber and black or green and black.
Gray-scale — Such types display different shades of grey.

2) Colour monitors — Also known as RGB monitors, they accept three separate signals — red, green and blue and are capable of displaying from 16 to1 million colours.

Colour monitors are, by far, the most popular today and are being used almost everywhere. Here we are elaborating this category for the benefit of our readers so that they can understand how they work.

The quality of coloured monitor depends upon the following:

CRT: Cathode Ray Tube or picture tube in a layman’s language is also used in the TV besides computer monitors. On the back of the monitor is a set of electron guns, which produces a controlled beam of electrons. The front portion of the CRT is coated with phosphorous chemical, with a pattern of red, green and blue. It gets illuminated when hit by a stream of electrons. This chemical is arranged into collection of millions of tiny dots. If you take a closer look at your monitor, you might be able to see these dots.

Refresh rate: Refresh rate means how many times per second the screen is refreshed to avoid flickering. The CRT has separate guns for the red, green and blue components of the image and powerful magnets determine the position of the electron beam of the three electron guns.

The gun first hits and glows the upper left corner of the screen. The graphics card in the computers order the monitor to scan or sweep the electrons briskly from left to right. The beam then returns to left from where it had started one line down and scans again. This process goes on repeating till the entire screen is covered.

This process is extremely fast. The number of horizontal scans that the monitor can make within a second is called horizontal refresh rate, which is measured in the range of 30,000 to 70,000 sweeps per second. In scientific terminology, a single sweep is known as one Hertz. Hence the horizontal refresh rate in this case might range from 30 KHz to 70 KHz.

A single vertical sweep during which the entire monitor is redrawn occurs about 60 and 90 times per second. Hence the entire screen is refreshed at a rate of 60 Hz to 90 Hz. This is known as the refresh rate.

To appear clear and flicker free, a monitor must operate with a refresh rate of at least 60 Hz.

Pixels or resolution: Resolution of monitor depends upon the number of pixels which are the images that are displayed on the monitor and are made up of different horizontal and vertical dots.

The resolution on a quality monitor is recommended at 800 x 600 pixels with the refresh rate of 85 Hz. This may go up to a maximum of 1024 x 768 pixel with a refresh rate of 60 Hz on a 14 or 15" colour monitor.

Dot pitch: Dot pitch is the diagonal distance between two dots (phosphorous) of the same colour. Generally speaking, smaller the dot pitch, sharper the displayed image. The good quality monitor should have 0.28 mm of dot pitch.

Viewable image size: The final feature is the size of the picture tube. The standard CRT size starts from 14 inches and proceeds as 15, 17, 19 and 21 inches. The size of the monitor is measured diagonally.

The retail price of the monitor depends upon the size and resolution. Bigger the size of the picture tube, clearer the picture will be. High resolutions are used only on the large monitors. Generally speaking, since the monitor is one of the most important interfaces with the computer, you should be well equipped with technical information when you set out to buy it.