the motherboard is the main motherboard. The only way you can have a main motherboard is if you have more than one in a computer witch are usually servers. 99.99999% of computer have one motherboard and that is the main object of a computer
cpu matherboard memory
GDDR3 is referring to the type of VRAM the graphics card has. If the graphics card is a pci-express one, then it can be installed into the motherboard if it has a pci-express slot available. DDR3 is referring to the type of Memory/RAM