A host system may couple to a PCIe subsystem. During setup of the PCIe subsystem, the BIOS in the host system may first be informed that the devices to be coupled are not PCIe devices, and certain amount of memory is required for these devices. The BIOS may therefore not attempt to configure the devices, and may instead allocate the required memory space. When the operating system boots up, it may not attempt to configure the devices, loading a custom driver instead of an existing PCI driver to configure the bus. Once loaded, the custom driver may configure the devices, then inform the OS that there are PCIe devices in the system at the specified addresses, which may cause the OS to load and execute existing PCIe device drivers to operate/use the devices. The proprietary driver may also be used to handle traffic between the PCIe drivers and the OS.