Sign in with
Sign up | Sign in
Your question
Solved

Whats best for sli PCI-E x16 both or x16/x8

Last response: in Graphics & Displays
Share
March 7, 2014 9:40:58 AM

I see motherboards with two PCI-E x16 and PCI-E x16 and the second slot is x8.
Should I buy the one with two PCI-E X16 slots? Does it affect performance when doing sli?

More about : whats sli pci x16 x16

a b V Motherboard
March 7, 2014 9:43:12 AM

Best is 2 x16.
There will be very little difference with x16 +x8, but if you are planning for SLI/xfire, you are aiming for very high performance, so I'd say that every percent counts.
And the motherboards with dual x16 are not that expensive.
m
0
l

Best solution

a b V Motherboard
March 7, 2014 9:52:23 AM

You are correct that two x16 lanes will give the best performance. However, all multi GPU will only ever have the need for dual x8 lanes, for now. The performance difference between two x16 lanes and two x8 lanes is very minimal, at best. Something like 1600 CL9 RAM vs 1866 CL9 RAM.

And motherboards with dual x16 lanes are actually quite expensive, and are usually associated with Extreme series CPUs (Two x8 lanes on an AMD board is quite rare, so talking about Intel here), so along with getting an expensive extreme series CPU, you'll need that expensive extreme series motherboard.

Most boards will support dual x8 lanes. A x16/x8 board is.. nonexistent? Because I believe if you're using SLI, it'll be using dual x8 lanes.
Share
Related resources
a b V Motherboard
March 7, 2014 10:01:31 AM

That is right. The real world question is: x16 + x4 or Dual x8.
And the real world answer is - it does not matter. The performance drop is minimal.
m
0
l
March 7, 2014 10:07:32 AM

enemy1g said:
You are correct that two x16 lanes will give the best performance. However, all multi GPU will only ever have the need for dual x8 lanes, for now. The performance difference between two x16 lanes and two x8 lanes is very minimal, at best. Something like 1600 CL9 RAM vs 1866 CL9 RAM.

And motherboards with dual x16 lanes are actually quite expensive, and are usually associated with Extreme series CPUs (Two x8 lanes on an AMD board is quite rare, so talking about Intel here), so along with getting an expensive extreme series CPU, you'll need that expensive extreme series motherboard.

Most boards will support dual x8 lanes. A x16/x8 board is.. nonexistent? Because I believe if you're using SLI, it'll be using dual x8 lanes.


So I cant get a mobo that is x16 + x8 if Im going to sli. The slots have to match?
If so Ill go with the x16 x2
m
0
l
March 7, 2014 10:10:25 AM

You can if you can find one, but the x16 drops to x8 in SLI anyway.
m
0
l
a b V Motherboard
March 7, 2014 10:11:14 AM

The performance difference between a motherboard running at x16/x4 is noticeable. That is a fact. A motherboard running at x8/x8 is considered optimal without breaking the bank for a minimal performance increase.

Motherboards will not run in x16/x8, it's either going to run in x16/x4 (these boards are usually for single GPU setups), or x8/x8 (multi GPU setups).
m
0
l
a b V Motherboard
March 7, 2014 10:53:14 AM

No one can answer this question correctly without more information. We need to know which chipset your considering because that will tell us the number of PCI-e lanes it supports. Each speed multiple takes up a lane. So, a PCI-e 16x slot can use up to 16 lanes, and 8x slot uses 8 lanes, etc.

For instance, the Intel Z87 chipset for the 4770k supports 16 PCI-e lanes. That means you can run SLI/Crossfire in an 8x8 configuration max. It doesn't matter what your PCI-e slots actually are. The result is that, even though you have 4 slots that are PCI-e v3.0x16, your expansion will not go beyond two video cards running in SLI or Crossfire at 8x each. It's just a limitation on the processor's chipset.

Another more important thing to consider is whether your processor can deliver information to the cards fast enough. That will likely be a bottleneck before the bandwidth of PCI-e, which has headroom to spare. So, pairing even an Intel i5-4670k with two gtx 780ti cards would likely result in a CPU bottleneck in certain use scenarios because of the processor being unable to feed both 8x PCI-e slots quickly enough. Just something to keep in mind.

Expansion turns out to be one of the primary reasons people buy into the Extreme platforms (e.g. X79 on the LGA2011 socket). For instance, the 3930k, 3960x, and 3970x, as well as this year's 4930k and 4960x, all support 40 PCI-e lanes. That gives you two GPUs running at 16x with 8 extra lanes left over. It's also part of the reason why SLI doesn't scale well past 2 cards. Another reason for poor scaling is that the SLI bridge's bandwidth is limited only to 1 GB/s, which is nothing compared to PCI-e v 3.0.

But I digress. Point is, the number of PCI-e lanes is an important consideration when you want multiple video cards or lots of expansion generally.
m
0
l
!