A question about PCIe lanes and how they are divided

"There is no one answer here:

The CPU has more than one means of interconnection depending on the CPU series. The CPU's connections can be directed to a PCH chip which can manage a greater number of PCI lanes.

So between the logic board and the CPU and how they work together will set the total number of lanes and then the lanes are distributed to the different slots as well as any dedicated interfaces on the logic board.

Update (01/04/2018)

Lets work off of a real CPU, chip set & logic board. Review these and focus your questions from these documents.

i7-8700K Processor which offers 16 PCIe lanesZ370 Chipset which in its self offers 24 lanesMSI logic board Z370-A-PRO Specs & Z370-A-PRO data sheet

Update (01/05/2018)

George, it’s not that cut & dry! Look at this diagram

As you can see the CPU’s PCI lanes are dedicated for graphics boards in this design."

"So, is there a way I can check how many PCIe lanes I have left on the chipset?

The GPU is obviously using some lanes? And I’m using 4 lanes for my new M.2 SSD.

Is there a way to check how many I have left because I want to add a capture card later and also another SATA adapter as well to get more SATA ports."

A answer to your request, is that there seems to be some usage of PCI-e lanes by motherboard manufacturers… which can be assigned better. For example offers the Asrock 990FX Extreme6 2x actual PCIe x16 slots being fully used while the 3rd x16 slot can at max operate @ x8. The onboard M2 slot uses the same resources as the eSata 3 port. I dunno who ever made usage of those ports but it seems to me, that some of those resources are used for unnecessary items. The same seems to apply to the new X570 chipset, where nothing else then a gfx card can be inserted, without having to suffer a downscaling, of the gen 4 x16 slot? That is really ridiculous and at least a bridge chip should be implemented between 2 x16 slots and the motherboard/CPU. Then the other slot would be free to put in high throughput storage cards. Two onboard M2 slots are already fantastic while more then can be freely added, with riser expansion cards. I want gfx cards to run on x16 to be ensured in the first place. Even when there is no software available yet. I want to c things running how they are meant to, without compromising in stuff, that came with the package, that I could not reject. Free architecture, was what the PC concept was all about, if I&I remembered correctly. Otherwise we would all stil use…. Amiga’s? Namasté

you have two types of pcie lanes, those that come directly from cpu and those that come from chipset, so the 10th gen intel X series cpu’s have 48 lanes which are directly wired to pcie slots so are extremly fast and each motherboard manufacturer decides on how to wire them to cpu, my msi creator x299 motherboard has 4 full sized (x16) pcie slots that run @ x16/0/x16/x8 0r x8/x8/x16/x8 (these are all directly wired to cpu) and these bifurcation (meaning seperating the lanes as needed is done by bios) varies by the type of cpu installed, so when someone says pcie lanes they mostly mean pcie lanes directly connected to cpu, then there is the x299 chipset and it is connected to peripherals like ethernet port, usb ports, sata ports and then it is connected to cpu with x4 pcie lanes, with non hedt cpu’s they only have 16 lanes coming from cpu that connect to pcie slots but during boot the bios determines if a slot should run at x8 or x16 speed based on what else is installed in the pcie slots that are directly wired to cpu, so if one has gpu in pcie slot closest to cpu and no other pcie devices in any other slots then it gets full x16 speed but if a nvme pcie drive is connected to one of those slots then gpu drops to x8 and nvme takes x4 and x4 lanes are remaining and some other pcie device like usb expansion for example can be installed.