agp is the graphic port on your motherboard. So is pci express. pci is just a port for all different sorts of things, like slow graphic card, sound cards, more usb ports, firewire ports, t.v. tuners, wireless cards, etc. Use the link I provided, scan your computer. Then go to display and click on the subtabs... there should be your port there, whether it be agp or pci ex. How old is your comp? If it's more than a year old... most likely agp. Less than a year... most likely pci ex. How expensive was it? All these quesions could help in deciding if you don't really know. Everest should tell you though... look around.