The purpose in adding a video card is to provide dedicated video memory (not shared with the main processor) and provide a dedicated video processor usually 64 bit to take the video processing load off the motherboard CPU. Video processing is a very intensive CPU activity, all the better to have it off loaded to a dedicated Video processor and leave the mother board or main processor to do it's intended job of running programs, services, printers and the like. At the same time motherboard RAM is totally dedicated to the main CPU and not shared with the video processor CPU thereby eliminating intermixed access cycles to motherboard RAM by the Main CPU and the video processor CPU.
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