Every computer display is composed of a rectangular array of pixels which are also known as picture elements. The more are the pixels, the more detailed information in form of the picture may be shown in a given amount of space on the display screen like the monitor of the computer. Each pixel displays a given number of distinct colours which is the colour depth of the pixel.
In order to work in co-ordination operating systems, graphics boards, and monitors support a number of standard video modes. As hardware has improved, and users have become more demanding, video modes have tended towards higher resolutions and greater colour depth. This requires a larger amount of dedicated memory, either on the computer motherboard, or on the graphics card.
XGA (Extended Graphics array) graphics standard was introduced by IBM in the year 1990.XGA was designed to replace the previous video standards. It is a high-resolution video display mode that provides screen pixel resolution of 1,024 by 768 supporting 256 colors per pixel or 640 by 480 in high color which has about 15 to 16 bits per pixel.
XGA monitors can be interlaced displays (Interlaced displays means that images can be displayed as low resolution images initially and then they can develop clarity and other details gradually. It can be used to create simple animations).
There are various video standard which supports different resolutions hence the quality of the display varies from one standard to another.
Resolution in pixels
VGA (Video Graphics Array)
640 x 480
SVGA (Super Video Graphics Array)
800 x 600
XGA (Extended Graphics array)
1024 x 768
SXGA (Super Extended Graphics array)
1280 x 1024
UXGA (Ultra Extended Graphics array)
1600 x 1200
The primary screen resolutions are 640×480, 800×600, 1024×768 and 1280×1024. At higher
resolutions, more of the document is visible with much more clearity and smoothness. On small monitors commonly resolutions like 640×480 and 800×600 are used. On 17 inch monitors, 1024×768 is common resolution which is a XGA standard. Resolution like 1280×1024 pixels and higher are used on 19 inch monitors which follows the video standards which are superior to XGA like SXGA AND UXGA.
Display adapters which provides a 1600×1200 resolution mode and even higher resolutions follows various standard video standards for medical and other demanding applications. In order to use the highest mode of the card, the monitor must be able to support that resolution.
XGA was an enhancement to VGA and has two modes known as XGA-1 and XGA-2.
XGA-1 supported a resolution of 800×600 pixels at 16-bits/pixel for 65,536 colors and 1024×768 pixels at 8-bits/pixel for 256 colors.
While the later version, XGA-2 offers 800 x 600 pixel resolution in true color with 16 million
colors having 24 bits per pixel and 1024 x 768 resolution in 65,536 colors. These two image
resolution levels are perhaps the most popular in use today in desktop computers.
XGA is a busmaster-based system meaning that a separate set of video processors take over much of the video processing task from the main system, allowing much faster performance while simultaneously releasing the main processor from video signal processing to perform other tasks. XGA provides resolution up to 1024 pixels by 768 pixels with 256 simultaneous colors and is said to be nearly twice as fast as IBM’s VGA graphics in MS-DOS mode.