_OSC Method and PCI Express in Windows Vista
The ACPI Operating System Capabilities (_OSC) method is used to communicate features or capabilities available in the platform which the operating system may take control of. This method is defined by ACPI 3.0 firmware specification and used in Microsoft Windows Vista.
Windows Vista and later versions of Windows operating systems use the capabilities defined in the PCI Express Base Specification and exposed in the ACPI 3.0 specification for controlling hot-plug insert/remove, Power Management Events (PME), and the PCI Express register features.
If the platform indicates in _OSC that control of any feature is not possible, or if the _OSC method is not implemented, then Windows Vista will not take control of any of the PCI Express features. This is new behavior from previous Beta releases of Windows Vista, in which these features were always managed by the operating system, regardless of the _OSC settings or presence.
This new PCI Express control will be present in Windows Vista beginning with the next CTP release. This change has the potential for degraded performance if the _OSC method is not present in the scope of a PCI root bus or if the firmware does not transfer control for PCI Express features as requested by the operating system.
Important: System manufacturers are encouraged to perform comprehensive test passes on their PCI Express-capable systems using the next CTP release. This testing will ensure compatibility of ACPI, PCI Express, and Windows implementations in firmware, hardware, and operating system capabilities.
