Dumb question on 6th gen I7 and PCI-Express lanes...

[The Internal]

So... my i7-6700k is in the mail already. However, it occurred to me that the 6700k only has 16x PCI-express lanes.
I plan on slapping the i7-6700k in a Gigabyte GA-Z170N-Gaming 5.

If I put a Samsung 950 Pro SSD (which uses 4x PCI-express lanes), does that mean I'll knock the 6700k down to 12 lanes available for my GPU (looking at the 1080 for this build) / limit it's bandwidth?

I'm planning on doing VR and possibly some 4k gaming with it, so I'm concerned I may have overlooked a potential bottleneck.

 

[Tsumi]

If you put the SSD on one of the slots that is connected directly to the CPU, yes, it will. Actually, switch the GPU to 8 lanes, as it can only function in x16 or x8. That being said, PCI-E 3.0 x8 is unlikely to bottleneck at GTX 1080.

However, your motherboard has PCI-E lanes available from the southbridge. Connect it to one of the slots connected to the southbridge, and you won't affect the lanes available to your GPU.

 

[needmorecarnitine]

I thought Z170 has 20 lanes

 

[The Internal]

I have no idea if the M.2 slot is connected directly to the CPU or through a chipset / controller on this motherboard. Does anyone know?

I thought Z170 has 20 lanes

According to intel ARK, Z170 is listed as supporting 20 lanes, though the 6700k is listed as only supporting 16 lanes.

 

[Tsumi]

I thought Z170 has 20 lanes

I have no idea if the M.2 slot is connected directly to the CPU or through a chipset / controller on this motherboard. Does anyone know?



According to intel ARK, Z170 is listed as supporting 20 lanes, though the 6700k is listed as only supporting 16 lanes.

The Z170 chipset does indeed have 20 PCI-E lanes. However, that is the chipset itself, not the CPU. The chip that is on the motherboard, that connects to the CPU via DMI 3.0. The chipset and the CPU have their own PCI-E controllers. The reason the Z170 chipset has 20 PCI-E lanes is because Intel is using something called Flex I/O. The picture below will demonstrate more clearly. Picture courtesy of Anandtech.

The first 3 PCI-E lanes can be used as USB ports or PCI-E lanes. #4 can be used as USB, Ethernet, or PCI-E. Lanes 9-12, 13-16, and/or 17-20 can be used for internal PCI-e storage devices, which are your M.2 PCI-E connected devices. That is where your 20 PCI-E lanes comes from, it is not at all related to the 16 GPU PCI-E lanes from the CPU.

 

[The Internal]

Thanks for the graph, Tsumi, but that still didn't answer the question...

Does using a Samsung Pro 950 M.2 (in PCI-E 4x mode) reduce the max lanes between the CPU and GPU to less than 16? Will "shared" or "flex" lanes negatively impact the GPU if a M.2 device is used? I'd also be using at least one additional drive, so it leads me to believe LGA 1151 simply can't support full-speed 16x GPU speeds with a M.2 and an SSD. Is that the case? Is it even an issue?

 

[Tsumi]

I did answer your question. You simply didn't read enough to understand my answer. Or you were too distracted by the big picture to properly read my answer. You would also have gotten your answer if you properly tried to understand the picture. Something happened where understanding wasn't happening.

I told you that the M.2 in Z170 boards is connected to the chipset. I also told you the chipset is not related in any way to the GPU PCI-E connections. If you look at the picture, the Intel PCIe Storage Device are your SATA-Express and M.2 connections. Using Device #1 on PCI-E slots 9-12 leaves 13-18 for use with SATA ports. Using Device #1 and #2 disables SATA 0-3, but you still have 4 and 5. Of course, the range of connections available is entirely up to the motherboard manufacturer. It's called Flex-IO for a reason.

 

[Trimlock]

Laymens terms:

Your GPU slots are connected directly to the CPU using the x16 lanes. Not all PCIe slots are connected to the CPU. The primary GPU slot will always be connected to the CPU.

Your IO SLOTS (example m.2) use the chipset PCIe lanes that connects to the CPU via the DMI channel. These don't use your 16 dedicated lanes.

Some m.2 slots do use the PCIE lanes that connects directly to the CPU. If you want to know that then look up your motherboard and see if it does. If it does then your GPU will run at x8.

I don't think x8 will choke your 1080.