One of the goals of PCIe when they were designing it was to avoid the “bus” architecture classic PCI had as that forced every device on the bus to run at the sp

One of the goals of PCIe when they were designing it was to avoid the “bus” architecture classic PCI had as that forced every device on the bus to run at the speed of the slowest device. PCIe, OTOH, takes a “star” network topology (more a "tree" though) with point to point connections. Thanks to the use of switches, each point can run at the maximum speed they support (limited by the switches speed). Basically, it’s like USB (as @dragontamer said). Just as you can turn a single USB port into 7 more downstream ports through a USB switch, you can do the same with a PCIe switch.