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Just to try and clarify a few things, there is a big difference between video cards and on-board video graphics chips.
On-board video graphics chips usually have a small amount of memory on chip with the most of the memory being shared memory. That is, using some of the system RAM.
On the other hand, most video cards have their own memory on the video card and usually do not use shared memory.
Another thing to consider is that many video cards come with various amounts of memory. An ATI 4350 video card (or any other model number) might have 256 mb, 512 mb, or 1024 mb of memory on the card. But then, an ATI 4350 on-board video chip will have very little memory on the chip with most of it's memory being shared.
The above is also true of nVidia video cards.
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