A graphics card is a pc minus the psu. It has its own graphics processing unit (gpu), it's own VRM's, it's own heatsink and fans, it's own voltage circuitry, it's own motherboard, it's own graphics ram. Totally separate and different from what's used in the pc as such. So makes absolutely no difference if the video card has ddr2, ddr3, gddr5 and the pc has ddr2. One doesn't mix with the other, the video ram is just for the video card use