Originally posted by: RebateMonger
	
	
		
		
			Originally posted by: ch33zw1z
However, you cannot use a cards with more lanes in slots with less lanes, ie: a 16x in 4x slot.
		
		
	 
Actually, I believe that you can. When the Dell SC420 came out, with its strange PCI-E 8X video slot in a PCI-E 16X connector, some folks successfully installed PCI-E 16X video cards in that 8X slot.
Dell was trying to prevent folks from using 16X video cards in the SC420. But Dell didn't want to create a whole new motherboard design. So they used a PCI-E connector that LOOKED like a 16X connector, but had extra separators built into the connector to prevent the insertion of a 16X video card. Folks got around this but burning away the separators. Those special PCI-E 16X connectors did NOT have all the pins connected. The pins were only connected for an 8X slot and were missing the 16X pins.
Anyway, to make a long story short, I understand that you may be able to use a 16X card in an 8X slot. But the card has to be designed to allow it. 
A short discussion of the SC420 16X card in 8X slot.