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How Are PCIe 3.0 Lanes Handled?

E

ElectroPulse

Limp Gawd
Joined
Aug 19, 2013
Messages
129
Hello, all!

My brother is preparing to build a computer in the near future, and has requested my help with it.

He's been eyeing the 6700k, and I've been doing some reading about it.

Currently his plan is 1x graphics card (he's looking at the 980 Ti), and possibly and M.2-based SSD. However, he's mentioned interest in possibly purchasing another identical graphics card down the road to use in SLI to prolong the life of his computer.

Now, with two graphics cards 8x + 8x, and an M.2 in 4x, that maxes out Skylake's 20 lanes. What happens if additional devices are added? (for example, a second M.2 SSD, or a video capture card, or a sound card). Can lanes be shared?

Thanks!
ElectroPulse
 
ElectroPulse said:
Now, with two graphics cards 8x + 8x, and an M.2 in 4x, that maxes out Skylake's 20 lanes. What happens if additional devices are added? (for example, a second M.2 SSD, or a video capture card, or a sound card). Can lanes be shared?

Thanks!
ElectroPulse
Click to expand...

A Skylake CPU has 16 lanes and the Z170 chipset has 20 additional lanes for 36 total. There are some limitations however, such as only being able to use CPU lanes for SLI. That is why you don't see Z170 boards that can do more than 2 way sli without a PLX chip. But basically, CPU lanes will usually be used for graphics, chipset lanes will usually be used for things like M.2 slots, etc.
 
GotNoRice said:
A Skylake CPU has 16 lanes and the Z170 chipset has 20 additional lanes for 36 total. There are some limitations however, such as only being able to use CPU lanes for SLI. That is why you don't see Z170 boards that can do more than 2 way sli without a PLX chip. But basically, CPU lanes will usually be used for graphics, chipset lanes will usually be used for things like M.2 slots, etc.
Click to expand...

Oh! That's how it works? Cool. I'd thought the overall limit was 20. Now that I think about it, that makes complete sense... A controller on the CPU, and the chipset on the board is another controller. No shortage of lanes there then. Thanks for the explanation, I now have a better understanding of how computers work.:)

On a side note, any ideas why there is a limitation of 2-way SLI, but 3-way crossfire? (it's marketed as such on Gigabyte's mobos)
 
limitedaccess said:
Nvidia has a restriction requiring each slot to be x8 or higher for SLI setups.
Click to expand...

To expand on that, Crossfire does not have this restriction, but I would say that 2 VGA cards is really only useful for 4k gaming, 3 and 4 way SLI are likely to cause more issues than it is worth.

I always had bad luck even with 2 way SLI, weird stuttering that made me want to punch the screen.

anyway end result you should be fine with z170 chipset.
 
I basically also feel that way. To me multi-gpu is more of a last resort option. You need a certain amount of performance and either you aren't willing to spend the single GPU performance equivalent or there is none. This applies more so as you add even more GPUs.
 
Ah, interesting.

Yea, I'd read there were some issues with >1 video card, but it didn't sound like there were so many with 2 (sounds like three are loads with >2). Was just curious as to the reasoning behind the statement of supporting 2-way SLI/3-way CrossFire :)
 
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