Interesting Stuff From Microsoft Hardware Developer Documentation

The Information below is taken from Microsoft Hardware Developement Document, Specifically Processor Power Management

Artificial Processor Performance State Domains

When Windows Vista and Windows Server 2008 were developed, several dual-core and dual-logical processor designs were prevalent in the marketplace. These CPUs typically provide one set of performance state controls that are shared across both cores or both logical processors, which implies that a control dependency exists. However, the system firmware for systems that have these CPUs targets earlier operating systems or otherwise predates the release of Windows Vista and therefore generally does not provide the ACPI 3.0 dependency objects. To support these popular processors without first requiring a platform BIOS update, Windows 7 creates an “artificial” processor performance state dependency domain for the operating system to use. Windows synthesizes a dependency domain for all logical processors in the same physical package. This is the default behavior for Windows 7, and therefore the _PSD object is not required to be present in the ACPI namespace to realize multiprocessor performance states on systems that are equipped with these dual-core processors.

For future systems that might provide two processor cores that share the same physical package but that have independent PPM controls, the default behavior of creating an artificial control dependency domain can be overridden in the following two ways:

· Include a _PSD object in the ACPI namespace that describes a separate dependency domain number for each logical processor or for each processor core.

· Create a DWORD value that is named PerfEnablePackageIdle under the following registry key and set its value to 1:

HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Throttle