Hi,
I bet your long gone, not having had an answer for so long. But if you do pop by here is my answer to your post.
Most PCs use two (not including processor cache here) types of RAM. One is on the mother board and is used by the processor for programs, variables etc. The other memory is on the Graphics card.
Recently (within the last few years) PCs have been coming out with much of the peripheral functions built into the motherboard, such as sound, ethernet and Video, instead of the plug in cards we are used to. ( I don't like them incidently - all your eggs in one basket sort of thing).
Their advantage being that they're cheaper.
Now a motherboard with a built in Graphics processor tends to share the motherboard memory between the CPU and the Graphics processor. this memory would be known as unified memory architecture ie. one memory different functions.
I bought my youngest son such a machine and it is noticeably slower than his brothers, who has a seperate graphics card and memory. The reason for it being slower is that you have 2 processors asking data from one memory. At some point you'll get both asking at the same time. Somone has to wait !.
So in short the motherboard memory is shared between the CPU and the onboard Graphics Processor.
Regards