Dell XPS 600 Owner's Manual page 83

NOTE:
If a graphics card is installed in each of the PCI Express x16 card slots in the dual-graphics
configuration, the PCI Express x1 card slot is not accessible for use.
• One PCI Express x1 card slot
PCI Express x16
card
PCI Express x16
card slot
PCI card
PCI Express x1
card
PCI Express x1
card slot
Removing and Installing Parts
83