PCIe lanes - question

[MarSio]

Hi,

I have a question. Intel i9-14900 has 20 PCI Express lanes.

Nvidia 4070ti uses 16 lanes. M.2 SSD used 4 lanes. This already gives 20 lanes. What happens if I have two M.2 SSDs? Will the GPU suffer or the other SSD suffer slower transfer? How is this resolved if there are more SSDs?

Kind regards.

 

[sck451]

There are 20 lanes connected directly to the CPU. There is then a link to the chipset (I think it's PCIe 4.0x8 on Z790, but I wouldn't swear to that); all other connected devices (M.2 slots, other PCIe slots, SATA, most USB) go through that link. On Z790 there are the 20 CPU lanes and then another 28 lanes connected through the chipset.

So the primary SSD (probably the boot drive) will go in the primary slot, connected to the CPU directly, while the others will be in secondary (/tertiary/etc) slots connected through the chipset. Theoretically there is a downside to this latter approach because the lanes are shared, but in reality you'll rarely encounter it.

Edit: You can actually see this in the Intel listing for the 14900: the dedicated chipset lanes are called Direct Media Interface/DMI. This is PCIe by another name: Intel's name for the reserved chipset PCIe lanes.