Video Graphics Array (VGA)

capable of a 640 x 200 display using 2 colors. Because of these limitations, the CGA adapter is generally considered obsolete. Enhanced Graphics Adapter (EGA) The enhanced graphics adapter (EGA) superseded the CGA adapter and drives an RGB monitor. The EGA provides 16 colors at a resolution of 320 x 200 or 640 x 200. The character box for text is 8 x 14 instead of the 8 x 8 used with the CGA card. The EGA card comes with 64K of video memory that is expandable to 256K using a graphics memory expansion card. This card adds an additional 64K of video memory. The EGA card also uses 128K of RAM from the computer’s RAM. The video is stored just above the 640K boundary. Video memory is used to refresh the display, freeing up the CPU chip for other operations. Video Graphics Array (VGA) The video graphics array (VGA) adapter card overcame the limitations earlier adapters had in displaying high quality color. The earlier adapters used digital signals to control the three electron guns of the CRT. Each gun was either turned on or off by these signals and limited the display to 8 colors. By adding a high and a low intensity signal, the number of colors that could be displayed was doubled to 16. The VGA card generates analog signals to control the electron guns and, therefore, can control the intensity of each gun at varying levels. Current VGA cards are capable of displaying 256 colors and generating 262,144 (256K) colors. Since the VGA generates analog signals, be sure the monitor is capable of accepting these signals. The VGA card displays text in a 9 x 16 character box and has a resolution of 640 x 480. Super Video Graphics Adapter (SVGA) Super video graphics array (SVGA) is a term used to describe graphic adapters that have exceeded those of the VGA system. As of now, there is no set standard for SVGA. Resolutions for SVGA vary by manufacturer but 800 x 600 and 1024 x 780 are common. Some SVGA cards work on a 60-Hz vertical scan rate and some use 70 Hz. Once an SVGA card is installed, a software driver that describes the specifications of that card needs to be installed. Extended Graphics Array (XGA) The extended graphics array (XGA) is a refinement of the VGA standard. The XGA system provides a 32-bit bus master for micro channel-based systems. The bus master has its own processor that allows it to operate independently of the motherboard, freeing the main processor. The XGA system also provides greater resolution and more colors than the VGA system. The XGA can hold up to 1M of video memory. Resolution is variable, depending on the mode selected. Maximum resolution is 1024 x 768, with the capability of displaying 256 colors from a palette of 262,144 colors. The XGA can also display 65,536 colors at a resolution of 640 x 480, providing almost photographic quality color. Video Adapter Maintenance As with the monitor, maintenance of video driver cards is generally limited to replacement of the card. Special test equipment is available for component level repair of some video drivers. LIQUID CRYSTAL DISPLAYS The development of laptop and notebook computers required a high resolution flat screen display with low power consumption. The most popular are passive and active matrix liquid crystal displays (LCDs). 2-3