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Erik
May 19th, 2010, 08:23 PM
CGA, or the IBM Color Graphics Adapter, was the original graphics option for the IBM PC and XT. It has 16Kb of video memory, an 8Kb character ROM, the Motorola 6845 CRT controller and a max resolution of 640*200 @ 2 colors. The most used graphics mode is however the medium-resolution 320*200 @ 4 colors. It also has several text-modes, most frequently used 40*25 characters or 80*25 characters, both @ 16 colors (independent back and foreground color, so there is a total of 256 combinations). However, the 80*25 character mode suffers from the phenomenon of "snow".
thumb|right|A CGA card
It connects to a TV-set through an NTSC-based composite output, or to a digital RGBI monitor (like the IBM 5153) through a 9-pin D-Shell connector. The character-quality is much better when using a RGBI monitor compared to a TV-set. IBM didn't offer any RGBI monitors before the introduction of the XT, and the only option for CGA users before 1983 was to use either the composite out or a genetic RGB monitor. Many of the generic RGB monitors then didn't support the intensity pin, and only 8 colors were available.
Several early PC application programs only support CGA.
Category:ISA cards