Chipsets

It's one chip on the motherboard. All other peripheral devices connect to it. In the past, there were two chipsets. In modern systems, much of the northbound chipset moved into the CPU. The memory controller is one such part.

The southbound chipset now connects to peripheral devices. It acts like a switch. It shares the same data bus between many devices.

Faster devices connect to CPU directly

Many faster devices connect to the CPU directly. They skip the chipset. For example, NVMe devices link straight to the CPU.

controller for PCI

For PCI devices, the chipset has no special controllers. It just checks the PCI packets. Then it passes them to the PCI controller in the CPU.