Asus MAXIMUS IV EXTREME-Z User Manual page 50

5. PCIe x16 Lane switch
These slide switches allows you to enable and disable the corresponding
PCIe x16 slots. When one of the installed PCIe x16 cards is out of order, you
can use the slide switch to find out the faulty one without removing the cards.
6. LN2 Mode switch
With LN2 mode activated, the ROG motherboard is optimized to remedy the
cold-boot bug during POST at an extremely low temperature and help the
system boot successfully.
2-18 Chapter 2: Hardware information