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You'd need a CPU with integrated graphics presumably, since it's not possible (currently, anyway) to route the video stream of an add-in graphics card through the motherboard's video output.

Hence you'd also be limited to the CPU's integrated video performance, which is less than stellar at the moment. It's currently useful for many regular desktop application activities for sure and is getting much stronger with each generation, but still weak when it comes to gaming.
 
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