PCIE lanes question help

[PCMaster2165]

I recently bought a powerful HP laptop which has an RTX 3060 (using 16 pcie lanes), 2 thunderbolt ports (I assume 2 x 4 lanes each), and two nvme ssd slots with one populated (I assume 4 lanes each). The CPU (i7 12700H) supports 28 lanes. If my math is correct it’s currently using all of them: (16 + (2x4) + 4) = 28. What will happen if I buy another SSD to fill the second nvme slot and use another 4 lanes? Where will they come from? Thanks for the help in advance. Here is the laptop: https://www.hp.com/ca-en/shop/product.aspx?id=378x7ua&opt=abl&sel=ntb

 

[Eigenvektor]

Usually some of the CPU's PCIe lanes go to the chipset, which then provides additional lanes, essentially bifurcating whatever it gets

[cleric_warlock]

It's hard to answer this question conclusively since I'm not sure how to go about finding the chipset diagram for your laptop. Whether or not your performance is impacted with the extra NVME ssd entirely depends on which components are routed to the cpu lanes vs which are routed to the chipset lanes that do not compete for bandwidth with the components hooked up to the cpu lanes. It's safe to assume that the ssd that's already there and the gpu are probably on cpu lanes, but i have no idea about the other components because I have no idea where to find the chipset diagram. If you're comfortable opening the laptop up to get a good look at the mobo, you might be able to see the traces that the lanes leave and inspect where they go.

[GOTSpectrum]

2 minutes ago, Eigenvektor said:

Usually some of the CPU's PCIe lanes go to the chipset, which then provides additional lanes, essentially bifurcating whatever it gets

To add to this, 

 

It's usually pretty handy to know which slots/ports are from the chipset as they have to share the bandwidth it has across all is it's devices. This means having multiple high performance devices on these lanes may cause issues like reduced frame rates, file transfer times ect ect depending on exactly which devices are sharing the bandwidth and the exact nature of the device.

 

 

[WoodenMarker]

4 minutes ago, cleric_warlock said:

no idea where to find the chipset diagram.

^

@PCMaster2165 Contact HP. 

[PineyCreek]

CPU has some PCI-E lanes then more come from the chipset.  The ones directly leading to the CPU are considered faster (lower latency?).  On desktops that's usually the top x16 slot and the top M.2 NVMe slot I think...varies per CPU/chipset.

 

ARK page for 12700H says 28 PCI-E lanes, CPU on PCI-E 4.0, Chipset on 3.0.

 

M.2. SSD is on 4.0, x4 lanes. In the spec sheet their secondary storage is listed using the same NVMe options, so highly likely your assumption about 16 (GPU) + 4 + 4 (2 NVMe on 4.0) is correct.  Probably safe to assume the dGPU is on x16?  I can't find a full chipset diagram either though.  iGPU isn't counted in CPU PCI-E lanes.
https://support.hp.com/us-en/document/ish_6507941-6507994-16

 

Note I'm basing this entirely on the specs of the drives listed for both primary and secondary being 4.0 and Intel's ARK page saying the lanes coming from the associated chipset are 3.0.  Perhaps the remaining x4 4.0 are going to the chipset as well.