which x16 pci-e slot for GPU?

[WhiteFireDragon]

i know that h55 chipsets are greatly neutered for SLI/xfire because the second pci-e slot won't run the full bandwidth. but if i only use one of the pci-e slot, then does it matter which one i use? i want to use the bottom one because of wire management configurations, but i think the GPU will only get x4 instead of x16, so can anyone confirm this? mobo is gigabyte H55M-S2H if that helps.

 

[ihira]

refer to motherboard user guide?

 

[J32P]

It's recommended that you use PCIe slot 1 as your motherboard will state.

That said, use any slot you want to, there will be little difference even if you use the x8 slot.


It shouldn't go to only x4 unless your MB is one I'm unfamiliar with, it should be x8.

 

[noquarter]

The limitation on the slower slots isn't just a result of how many cards you have in there, it's because they only trace 4 PCI-e lanes out to the 3rd slot, and 8 PCI-e lanes to the 2nd slot, it saves money. (assuming an x16/x8/x4 mobo)

In mobos that are x16/x0 -> x8/x8 there are usually 16 lanes to slot 1 and 8 of those lanes also go to slot 2 so using slot 2 steals away those 8 lanes from slot 1.

Your mobo you definitely don't want to use the bottom slot though, it's a PCI-e 1.0 x4 slot which is the same bandwidth as a PCI-e 2.0 x2 slot.

 

[Machine-code]

I was about to start a thread with the same question.

I have a Rampage II Gene and both PCIe slots are x16. The manual recommends using the first slot. Can I use the second slot instead without taking a performance hit.

Why does the manufacturer tell you this if both slots are x16? I would really like to use the first slot to mount some fans to cool the toasty NB. thanks

 

[Hornet]

x58 boards should have at least 2 PCIE 16x slots with full physical connection, and you should be able to use any of these slot with no performance hit

 

[Machine-code]

Thanks. Parts of my manual don't apply to my MB. I think parts of the manual are copied from other manuals hence their advice to use the first slot.

 

[WhiteFireDragon]

yeah i just verified with my manual that the gigabyte H55M mobo only has the first slot at x16 and the bottom slot at x4.

so for x58 chipsets with 4 pci-e slots, i can use all 4 for the full x16 or is it only the top two since it doesn't have the nf200 chip? this is the EVGA x58 LE mobo. and would i have to reinstall video drivers if it's already running on the first slot and i switch it down one or two slots?

 

[Hornet]

yeah i just verified with my manual that the gigabyte H55M mobo only has the first slot at x16 and the bottom slot at x4.

so for x58 chipsets with 4 pci-e slots, i can use all 4 for the full x16 or is it only the top two since it doesn't have the nf200 chip? this is the EVGA x58 LE mobo. and would i have to reinstall video drivers if it's already running on the first slot and i switch it down one or two slots?

No, you can't have full x16 if you use all 4. x58 only have 2 x16 lanes, so if you use all 4 slots, each card will only have PCIE x8 lanes

You can use two x16 slot, which one it is depends on your motherboard.

My Gigabyte UD7 board layout is:
PCI-E16 1_1 - x16
PCI-E16 1_2 - x8
PCI-E16 2_1 - x16
PCI-E16 2_2 - x8

So I have to use the first and 3rd slot to get x16 for both cards

Most board with 4 PCIE 16 slot should have such layout, unless there is extra space between the first and 2nd slot, as these x16 slots are expected to be used for dual slot graphic card. So it makes no sense to put 2 x16 slot next to each other

But anyway, consult the board's manual to see which slot you should use for 2 card setup

 

[rennyf77]

evga x58 le won't do 16/16 cf or sli. here are the speeds of the four slots top to bottom. 16x, 4x, 8x, 8x. these speeds won't change regardless of where you slot your cards. i don't know why they did this but that's how it works. i just realized earlier to day that my 5870 cf array was running in 16/4 as i wanted some space between the cards. moving the bottom card right underneath the top card leaves me with a 16/8 cf array.

 

[WhiteFireDragon]

ah ok, i guess slot placement is very different on every board. i always thought that if you only use 1 card, you get the full x16 no matter which slot you put it in on x58 chipsets, so this is wrong? the lanes never changes and are locked to each slot?

 

[InvisiBill]

ah ok, i guess slot placement is very different on every board. i always thought that if you only use 1 card, you get the full x16 no matter which slot you put it in on x58 chipsets, so this is wrong? the lanes never changes and are locked to each slot?

Yes, that's wrong.

The limitation on the slower slots isn't just a result of how many cards you have in there, it's because they only trace 4 PCI-e lanes out to the 3rd slot, and 8 PCI-e lanes to the 2nd slot, it saves money. (assuming an x16/x8/x4 mobo)

Sometimes the physical slots share lanes, so it just "steals" them from the other slot if you install a card. Other times, they don't physically connect as many lanes to all slots, so those slots simply can't use more lanes.

This is one benefit of the original EVGA X58 having one less PCIe slot. While the newer ones are 16-4-8-8, the original is 16-16-8.

 

[noquarter]

Sometimes the physical slots share lanes, so it just "steals" them from the other slot if you install a card. Other times, they don't physically connect as many lanes to all slots, so those slots simply can't use more lanes.

Yea, I even used the word steal in the 2nd line of my post you mustn't have read before quoting Regardless the slower slots have less lanes traced to them even when they steal those lanes from the primary slot, making it impossible to run at 16x.