VIDEO MODES

8/30/97

Video Modes: A Video Mode is a specification for the number of picture elements ("pixels") horizontally, and vertically; the number of colors, and whether the display is interlaced (alternate lines displayed on each pass) or non-interlaced. Together, these four parameters dictate how often a given monitor can be updated ("refreshed"). Monitors must be refreshed 30 or more times per second in order for the picture not to flicker. Refresh rates close to 50/60Hz may appear to flicker if viewed in fluorescent or other pulsed lighting sources.

Five major display schemes have been used in IBM compatible PCs -- Monochrome, CGA, EGA, VGA and SVGA. (There have been less used schemes as well -- PGA for example). All types support different screen resolutions and all except monochrome support different color combinations. Thus, each type of monitor must support multiple different video modes. In the case of an SVGA multisynching monitor, the monitor may have to support over 100 different modes. Failure to synchronize properly will result in a blank display; a display with many unintelligible horizontal lines; a display that rolls vertically or horizontally; multiple pictures; etc.

It is possible to use a secondary monochrome monitor with a different display in conjunction with almost any color monitor. This does not affect the modes(s) available for either monitor.

A monitor has a maximum input frequency which must be respected and will dictate the maximum resolution and number of colors that can be used. The graphics adapter card and driver software will dictate what modes can be attempted. However, monitors may not be able to synchronize with all video modes available from a given graphics card. Even if the monitor can synch with all modes, the display size and positioning may shift with the mode. Top end monitors store user set screen size and positioning information for each mode. Less expensive monitors may require manual adjustment of these parameters for each display mode used.

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