Why 16x-4x rather than 16x-16x in crossfire


Oct 5, 2011
i just got done building a gaming rig, and noticed my second graffics card is running 4x. its an asus sabertooth 990fx, and i'm running radeon 6770's in crossfire. ( 6770, i know, but i had one in my old computer and salvaged it and decided it was cheaper to buy another one and run xfire, rather than buy a higher end card) is there something i have to do in the bios to set it up as 16x. i am running the cards in slot 1 and 3, which are both 16x.
According to your user manual, page 2-15, inserting your vid cards in slots 1 & 3 should auto-result in 16-16 operation. A quick scan of the bios section of your manual did not show me a related bios setting, so it should all happen automatically.

Are you *certain* you are using slots 1 and 3? Please note that slot #3 may NOT be the third PCIE slot. The first physical slot is almost certainly the real "Slot 1", but check the identifier on the board near the socket and find the slot labelled "PCIe 2.0 x16_3" or something similar.