Asus P5K64 WS - Manual (Page 44)

2-18 Chapter 2: Hardware information
2.5.4 PCI slots
The PCI slots support cards such as
a LAN card, SCSI card, USB card,
and other cards that comply with PCI
specifications. The figure shows a LAN
card installed on a PCI slot.
2.5.5 PCI Express slots
This motherboard has four PCI Express
slots that support PCI Express graphic
cards complying with the PCI Express
specifications.
This motherboard supports two ATI
CrossFire™ PCI Express graphics
cards that comply with the PCI Express
specifications.
We recommend that you install a VGA card on the primary (blue) PCI Express
slot, and install any other PCI Express device on the Universal PCI-E slot
(black).
Primary PCI Express x16 slot
The primary PCI Express x16 slot supports PCI Express x16 graphic cards that
comply with the PCI Express specifications.