Bit-mapped display screens permit the computer to manipulate pixels on the screen individually rather than as blocks, enabling the software to create a greater variety of images. Today most screens can display text and graphics- icons, charts, graphs and drawings.
For a computer to display bit-mapped graphics, the display screen must have a video display adapter. A video display adapter, also called a graphics card, is a circuit board that determines the resolution and how fast images appear on the display screen. Video display adapters come with their own memory chips, which determine how fast the card processes images and how many colors it can display screen. Video display adapter come with their own memory chips, which determine how fast the card processes images and how many colors it can display. A video display adapter with 256 K of memory will provide 16 colors; one with 1 megabyte may support 16.7 million colors.
The video display adapter is often built into the motherboard, although it may also be an expansion card that plugs into an expansion slot. Video display adapters embody certain standards. The MDA and CGA standards are no longer favored; newer computer displays tend to favor VGA, SVGA, or XGA standards:
VGA: Perhaps the most common video standard today, VGA, for video graphics, will support 16 to 256 colors, depending on resolution. At 320 × 200 pixels it will support 256 colors; at the sharper resolution of 640 × 480 pixels it will support 16 colors.
SVGA: SVGA, for super video graphics, will support 256 colors at higher resolution than VGA. SVGA has two graphics modes: 800 × 600 Pixels and 1024 × 768.
XGA: Also referred to as high resolution display, XGA, for extended graphics that is supported up to 16.7 million colors at a resolution of 1024 × 768 pixels. It is depending on the video display adapter memory chip, XGA will be supported color 256 or 65,536 or 16,777,216.
For any of these displays to work, video display adapters and monitors must be compatible. Your computer’s software and the video display adapter must also be compatible. Thus, if you are changing your monitor or your video display adapter, be sure the new one will still work with the old.