Question about PCIe lanes with M.2 and GPU

[tjgreenwood1996]

Mobo: ASUS z270e
GPU: GTX 1080
CPU: i7700K

Excuse my ignorance, I'm looking into adding an M.2 as a boot drive and some game storage.
However from what I've seen the 7700K is limited to 16x lanes?

My question is, if I used an M.2 in PCIe 3.0 x4 mode, would it limit my GPU to PCIe 3.0 x8 instead of the usual x16?
Or would the M.2 use the PCIe lanes from the chipset instead of the ones allocated for GPU?

May be a dumb question, but I've reached the limit of what I can decipher from the mobo manual.
Don't want to go messing up my GPU performance when I could just use a SATA SSD, but would like the faster pcie speed if possible...
Thanks!

 

[nitinvaid20]

it will use the PCI lanes from the Chipset

 

[Snipergod87]

Depends on how the PCI-Express lanes are divided up, if they go through the PCH via DMI 3.0 or directly to the CPU, also dropping from 16x to 8x PCI-Express 3.0 will have a less than 1% performance impact.

 

[raisonjohn]

This chart/block diagram is what you need (not found in the manual):

As you can see, all PCIe lanes of your two top PCIe x16 slots for your GPU is controlled by the CPU (16x PCIe lanes), where using the top slot will run at x16 and using the two slots will run at x8/x8 (total of x16).

The M.2 slots, in PCIe-mode, in your motherboard are all controlled by the Z270 chipset. The M.2_1 slot will only share bandwidth with the SATA 1 port if such M.2 slot is in SATA-mode, but will not disable any ports if run in PCIe-mode. The M.2_2 slot will disable two SATA ports (SATA 5 and SATA 6) when running in PCIe X4-mode

 

[tjgreenwood1996]

This chart/block diagram is what you need (not found in the manual):

As you can see, all PCIe lanes of your two top PCIe x16 slots for your GPU is controlled by the CPU (16x PCIe lanes), where using the top slot will run at x16 and using the two slots will run at x8/x8 (total of x16).

The M.2 slots, in PCIe-mode, in your motherboard are all controlled by the Z270 chipset. The M.2_1 slot will only share bandwidth with the SATA 1 port if such M.2 slot is in SATA-mode, but will not disable any ports if run in PCIe-mode. The M.2_2 slot will disable two SATA ports (SATA 5 and SATA 6) when running in PCIe X4-mode

Perfect, exactly what I was looking for!
Thanks so much