Asus P5K/EPU - Manual (Page 46)

2-22 Chapter 2: Hardware information
Primary PCI Express x16 slot
The primary PCI Express x16 slot supports PCI Express x16 graphic cards that
comply with the PCI Express specifications.
Universal PCI Express slot (max. x4 mode)
This motherboard also supports a Universal PCI Express slot with a maximum
speed of 2 GB/s. The operating frequency of this slot changes, depending on the
type of PCI Express card you install. Refer to the table below for details.
The figure shows two graphics cards installed on the primary PCI Express x16 slot
and the Universal PCI Express slot.
If you install two VGA cards, we recommend that you plug the rear chassis
fan cable to the motherboard connector labeled CHA_FAN1 for better thermal
environment. See page 2-30 for the connector location.
• Some PCI Express graphics cards cannot operate on x4/x1 mode. We
suggest that you install these cards on the primary PCI Express slot (blue)
to increase system stability.
• Some PCI Express devices cannot operate on x4/x1 mode.
Options for Universal
PCI Express slot
PCI Express operating speed
Auto Automatically optimizes performance and
functionality according to devices installed
x4 mode [fast] User gets the best performance but this mode
disables the PCI Express x1 slot
x1 mode [compatible] Always runs at PCI Express x1 speed