I would appreciate of someone can explain the difference between
a PCI bridge and a PCI switch.
With good ol' PCI, a single bus can have many devices. A PCI bridge
is a device that connects multiple buses together, which is something
that was very seldom needed.
PCI Express looks, for software, very similar to PCI, but is electrically
a point-to-point connection, i.e., a PCIe bus has exactly two devices.
To connect PCIe with PCI, you need a PCI/PCIe or PCIe/PCI bridge.
If you have a single PCIe connector and multiple PCIe devices, you need
a PCIe switch. A single PCIe connection still is between exactly two
devices, so a PCIe switch consists of a (virtual) PCI bridge for the
upstream PCIe connection, and one (virtual) PCI bridge for each
downstream PCIe connection.