To understand the Root Complex, you have to visualize the "PCIe Fabric" as an inverted tree.

These are the Endpoints . An endpoint is any functional device at the end of a PCIe link, such as a GPU or a Sound Card.

Modern root complexes (e.g., in Intel Core 12th–14th gen or AMD Ryzen) provide dedicated lanes (x16 for GPU, x4 for NVMe) directly to the CPU. This reduces contention and delivers near-theoretical PCIe 4.0/5.0 speeds.

It handles the flow of data packets. It ensures that a "Read" request from the CPU reaches the correct SSD and that the "Data" packet finds its way back.