PCIe is designed to be copatable to the leagcy PCI. It preserves the software model so that:

• BIOS routines (for device discovery & configuration)
• Operating system code (plug-and-play, resource allocation)
• Device drivers (control & data transfer)

all continue to work without modification.

How PCIe Achieved It

• Same Address Spaces:

  • Memory space, I/O space, and Configuration space still exist in PCIe.
  • They are programmed the same way (same registers, same configuration mechanisms).
  • Some spaces are simply extended to allow for more features and larger address ranges.

• Extended Configuration Space:

  • PCIe adds many new registers to support:
    • Power management
    • Advanced error reporting
    • Hot-plugging
    • Quality-of-service
  • But the legacy PCI registers remain intact, so old software can still interact with the device in the familiar way.