PCI came out first, thats the only slot the video card came in, so they were really good like 8 years ago or whatnot i dont really know, then AGP started to come out, with newer and better video cards. SO PCI was still there but started to age and they quit making PCI video cards, and only AGP cards. Now PCIE16 is out, and now they are stop making AGP cards and only making newer and better PCIe16 cards. and now PCI is usually used for just sound cards, network cards, and some video cards if you have a dell or something