The PCI Express Upstream Switch Port is a term that typically refers to a hardware interface used for managing data flow between devices on a PCI Express (PCIe)PCIe device (like a graphics card, network card, or storage controller) and the CPU or other components in your computer.

When you see the "PCI Express Upstream Switch Port" listed in Device Manager in Windows, it's often related to the PCI Express root port or a PCIe switch in your computer's motherboard. This port is part of the PCIe infrastructure that allows devices to communicate with each other via the PCIe bus.

If Windows is unable to recognize the device properly, you might see an entry like "PCI Express Upstream Switch Port" in Device Manager with an exclamation mark, indicating that the driver is missing or not working correctly.