AGP 1X-2X is 3.3 volts and 4X-8X is 1.8 volts. If the board slot has a separator in the front of the slot is a 1X-2X slot, if its in the back its a 4X-8X slot,now they made a universal slots but thats another story! Now to the cards, if the card has a slot in the front its a 1X-2X card and can not be inserted in a 4X-8X slot. If the slot is in the back its a 4X-8X card and canot be inserted in a 1X-2X slot, now thay make 4X-8X cards with slots in the front and back and can be used in either board because they are backward compatible to run in 2X mode at 3.3 volts