Question More than 16 PCIe 3.0 lanes on Z77 motherboard?

[edwjohn3]

Hello,

I have recently added an NVMe SSD to my ASRock Z77 Extreme4 motherboard (CPU is an i5 3570k). The motherboard does not have an m.2 slot so I have connected the drive to the board's second PCIe x16 slot via an m.2-PCIe adapter card. I am now booting Windows 10 from the NVMe SSD. It seems to be working perfectly and I am getting CrystalDiskMark sequential read and write speeds 5x those of my SATA SSD.

My issue is this. It was my understanding that with this CPU/motherboard there are a total of 16 combined lanes of PCIe 3.0 available to the two 16x slots. So I was expecting that when I installed the SSD into the second slot, my Vega 56 would drop down to 8x mode. However, the AMD graphics drivers and GPU-Z are both reporting that the graphics card is still running in 16x mode, and ADATA's SSD Toolbox utility is telling me that the SSD is running in PCIe 3.0 4x mode. This adds up to 20 lanes of simultaneous usage which I do not think is possible.

Does anyone have any thoughts on what might be going on or if there are any utilities that will more accurately report exactly how many lanes and what generation of PCIe each device is using? I am getting 2800 MB/s of sustained read and write from the SSD so I don't think it is running in PCIe 2.0 mode.

ASRock Z77 Extreme4 running UEFI version 2.90P
i5 3570k @ 4.2 Ghz
AMD Radeon RX Vega 56 in primary PCIe x16 slot
16 GB DDR3
ADATA XPG SX8200 Pro 1TB NVMe SSD in secondary PCIe x16 slot

Thanks

 

[karenjoly]

There are lots of lanes available. The cpu has 16 and the chipset likely another 24. The cpu lanes here go through pcie2.The manual says that video cards in pcie 2 and 3 run both at x8, so who you gonna believe ? Anyway manual says nothing about M.2 adapters. Finally what adapter ?

 

[edwjohn3]

I looked up the specifications of the Z77 chipset. It is capable of providing up to 8 lanes of PCIe 2.0 connectivity, so the only gen3 lanes would be coming from the CPU.

The adapter I'm using is this: https://www.newegg.com/Product/Prod...ilverstone_m.2_adapter-_-15-256-024-_-Product

 

[edwjohn3]

I downloaded AIDA64, which is reporting that the GPU is running in x8 mode as expected.