Display Adaptors

Various kinds of monitors are available—black and white or color—some displaying sharper images than others. Images are formed on the monitor's screen by a card called the display adapter card.

The key elements of a display adaptor are the video controller and the memory. As you know, the results of your interaction with the PC are displayed on the screen of the monitor. The information to be displayed on the monitor need to be stored somewhere so that it can be displayed. The memory on the adaptor card holds this data. The video controller is responsible for forming the image on the screen using this data. This memory is also accessible by the microprocessor so that changes can be made to the data when required. The time taken for reading the display memory and displaying a new picture on the screen is roughly one-fiftieth of a second. If a program wants new information to be displayed, it places the data in the display memory and it is reflected almost instantaneously on the screen.

Several kinds display adaptors exist in the market, each with its own special features. Some of the parameters that are used to distinguish between the various display adaptors are:

  • Display in text mode
  • Resolution in graphics mode

The PC can represent data on the screen in two modes. One is the text mode in which only text or individual characters can be displayed. The other is the graphics mode, where graphics (pictures) can be shown by constructing an image on the screen using dots.

In the text mode, the VDU screen is divided into specific character positions—usually 80 columns—of characters across the width of the screen and 25 lines of characters from top to bottom. Most, but not all, display adaptors support display of text on the screen.

In the graphics mode, the screen is treated as an array of tiny dots called pixels (short for picture elements), and anything that appears on the screen is shown using these dots. Each of these dots can be set on or off on the screen.

In the graphics mode, a parameter that can further differentiate between various display adaptors is resolution. Resolution of the screen indicates the number of dots or pixels on the screen. A typical high resolution display has 640 columns of dots across and 480 rows of dots down the screen. Besides, the display adaptors, that support graphics, have different resolutions. The higher the resolution (i.e. more the number of pixels), the better the quality of pictures displayed on the screen.

Yet another parameter used to differentiate between display adaptors is whether they support color or not. There are two types of monitors—monochrome (i.e. black and white) and color.

The monitor you have needs to be compatible with the adaptor card. It would be no use having a color monitor with a display adaptor that does not support color; or having an adaptor that supports high resolution with a low resolution monitor.

Since the resolution and the number of colors increase with increasing sophistication of display adaptors, the pixels require increasing amount of memory. Thus, the amount of memory on the display adaptor has to be increased.

Having considered the main parameters used to evaluate the display adaptors, you will now study some of the popular display adaptors supported by the PC.

=> Enhanced Graphics Adaptor adaptors (EGA)

=> Video Graphics Array adaptors (VGA)

=> Super Video Graphics Array adaptors (SVGA)