question about pci-e 16 slots in motherboards

[travisbrummett]

i noticed in all the details for motherboards that have 2 pci-e 16 slots, that it says it has 2 pci-e 16 cards running at 8x. does that mean if i only have one card it runs at 8x and i lose quality from a video card? do they make motherboards with 2 pci-e 16 slots that run at 16x even if theres only one card in there?

 

[pdc76]

some boards share the 16x bandwidth, splitting it into 2 8x slots when using 2 cards (true for both sli and crossfire). there are some boards that will run each slot at the full 16x too. in either case if you only use one card it will run at 16x speed.

 

[travisbrummett]

ok i get it. so when i use 2 cards in a motherboard that has 2 pci-e it will do 32x?

 

[pfig88]

ok i get it. so when i use 2 cards in a motherboard that has 2 pci-e it will do 32x?

nope, they'll either each run at 16x or 8x. 16x is the maximum the PCI-E slots can handle

 

[StrangleHold]

Its a chipset limit they place on PCIe lanes. Like AMD 790FX has 42 PCIe lanes. They kill a certian amount of PCIe lanes on the 790X and 770 ( which is the same chipset as the 760/780, they just have onboard. So the lowend chipsets have less PCIe lanes.

If you run Crossfire on a 790FX chipset you have between the two slots 32 PCie lanes 16X-X16. On a 790X board in Crossfire you have two slots running a 8X -8X for 16 lanes total. But if you run one card all the 770/790X/790FX will run a single slot at X16 lanes.

 

[pfig88]

Its a chipset limit they place on PCIe lanes. Like AMD 790FX has 42 PCIe lanes. They kill a certian amount of PCIe lanes on the 790X and 770 ( which is the same chipset as the 760/780, they just have onboard. So the lowend chipsets have less PCIe lanes.

If you run Crossfire on a 790FX chipset you have between the two slots 32 PCie lanes 16X-X16. On a 790X board in Crossfire you have two slots running a 8X -8X for 16 lanes total. But if you run one card all the 770/790X/790FX will run a single slot at X16 lanes.

Exactly