For the last couple of normal desktop platforms from Intel. The CPU itself has a PCIe controller that drives up to 16 PCIe lanes and an additional 8 PCIe lanes are driven by the PCIe controller on the PCH. The PCH is linked to the CPU through a DMI. It is a similar setup on the last couple of AMD platforms but their southbridge use a PCIe link to talk to CPU.
Gigabyte X670 AORUS-ELITE AX, Raphael 7950X, 2x16GiB of G.Skill TRIDENT DDR5-5600, Sapphire RX 6900XT, Seasonic GX-850 and Fractal Define 7 (W)
Ivy Bridge 3570K, 2x4GiB of G.Skill RIPSAW DDR3-1600, Gigabyte Z77X-UD3H, Corsair CX-750M V2, and PC-7B