Geforce8400 GS requirements

They come in both flavors. Just pay attention to the box, it'll tell you if it's PCI or PCI-E, or if ordering on-line it will tell you in the discription.

PCI
http://www.newegg.com/Product/ProductList.aspx?Submit=E...

PCI-E
http://www.newegg.com/Product/ProductList.aspx?Submit=E...

The 8400gs is Nvidia's x300se and most of these ultra low end cards are garbage. So I suggest that if your computer has a pci-e slot that you purchase something better but if much older and only has a pci slot then your choices are limited and you shouldn't be buying any thing that is high cost when you should at the very least start upgrading out the board and cpu. If it is a oem computer like Dell or HP then you made a mistake of buying one.