There are three basic types of add-on cards.  The card on the far left is an example of an ISA card.  This card uses a 16 bit bus and is found in older computers.  This card plugs into the long, black slots on a motherboard.  The card in the middle is a PCI card.  PCI cards run on a 32 bit bus and are found in newer computers.  The PCI card plugs into the short, white slots on a motherboard.  The card on the right is an AGP card. This card accesses the processor directly for higher graphics speeds.  AGP cards are primarily video cards and plug into the short, tan slot on a motherboard.