A system and method for using memory mapped I/O (MMIO) to manage system devices is provided. A parent device in the ACPI namespace uses (MMIO) to identify the memory addresses of its children devices. An existing, but unused, construct of ACPI is used to pass the MMIO information through the operating system (OS) to the device drivers, enabling memory to be reserved by a device, and also remain hidden to the OS. The vendor defined resource data type for long information, also known as the "vendor-long" descriptor, is used to pass the appropriate information through the OS.