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Extended PSS ACPI Method Specification

Updated: April 19, 2007

The Extended PSS (XPSS) method is an ACPI method that allows platform firmware to generically describe a Model Specific Register (MSR)-based interface for processor performance state controls. This enables the use of the generic processor driver included with Windows, without requiring a specific Windows processor driver developed by Microsoft and designed expressly for the target platform.

This information applies for the following operating systems:
Windows Vista
Windows Server 2008

Included in this white paper:

  • Background
    • Processor Driver Support in Windows
    • Rationale for Extending the _PSS
  • Requirements for Using the XPSS
  • The XPSS (Extended Performance States)
  • Implementing the XPSS Interface
  • Getting Help
  • Resources

Please read the license agreement before continuing.



IMPORTANT—READ CAREFULLY: This Microsoft License Agreement ("Agreement") is a legal agreement between you (either an individual or a single entity) and Microsoft Corporation for the version of the Microsoft document identified above which you are about to download ("Specification"). BY DOWNLOADING, COPYING OR OTHERWISE USING THE DOCUMENT, YOU AGREE TO BE BOUND BY THE TERMS OF THIS AGREEMENT. IF YOU DO NOT AGREE TO THE TERMS OF THIS AGREEMENT, DO NOT DOWNLOAD, COPY, OR USE THE DOCUMENT. The Document is owned by Microsoft or its suppliers and is protected by copyright laws and international copyright treaties, as well as other intellectual property laws and treaties. THE DOCUMENT IS LICENSED, NOT SOLD.


  1. Provided that you comply with all terms and conditions of this Agreement, Microsoft grants to you the following non-exclusive, worldwide, royalty-free, perpetual, non-transferable, non-sublicensable, limited license under any copyrights or patents that cover the Extended PSS (XPSS) ACPI method described in the Specification and that are owned or licensable by Microsoft without payment of consideration to third parties,

    1. to reproduce copies of the Specification for you and your contractor's internal use for the sole purpose of (1) modifying your firmware and/or BIOS for computing devices ("Firmware") so that it writes to memory the appropriate XPSS ACPI method in the Specification or (2) modifying your software so that it may read from memory the appropriate XPSS ACPI method (the "Purpose"),

    2. to implement the XPSS ACPI method in your firmware and/or BIOS,

    3. to license to third parties directly and indirectly the XPSS ACPI method as part of your Firmware (and any related documentation),

      The foregoing license is granted only to the extent necessary to accomplish the Purpose and to license and/or distribute your Firmware containing the XPSS ACPI method to third parties. The foregoing license shall not extend to any features of your Firmware that (i) are not required to comply with the Specification or (ii) to which there was a practicable alternative to infringing a patent.

  2. Microsoft reserves all other rights it may have in the Specification, its implementation and any intellectual property therein. The furnishing of this Specification does not give you or any other entity any license to any other Microsoft patents, trademarks, copyrights or other intellectual property rights. Microsoft does not grant to you or any other entity any implied licenses or rights whatsoever under this Agreement. Specifically, this Agreement does not grant any express or implied licenses or rights to any enabling technologies that may be necessary to fully utilize the XPSS ACPI method described in the Specification.


  1. You must implement XPSS Interface in its entirety (e.g., all fields) and without modification (e.g., parameter encoding and permissible values as described in the Specification).

  2. Your license rights to the Specification are conditioned upon you not creating, modify, or distributing your Firmware in a way that such creation, modification, or distribution may (a) create, or purport to create, obligations for Microsoft with respect to the Specification (or intellectual property therein) or (b) grant, or purport to grant, to any third party any rights or immunities to Microsoft's intellectual property or proprietary rights in the Specification.

  3. The foregoing license is applicable only to the version of the Specification which you are about to download. It does not apply to any additional versions of or extensions to the Specification.

  4. Without prejudice to any other rights, Microsoft may terminate this Agreement if you fail to comply with the terms and conditions of this Agreement. In such event you must destroy all copies of the Specification and must not further distribute the table values.

3. INTELLECTUAL PROPERTY RIGHTS. All ownership, title and intellectual property rights in and to the Specification, and any copies you are permitted to make herein, are owned by Microsoft or its suppliers.

4. DISCLAIMER OF WARRANTIES. To the maximum extent permitted by applicable law, Microsoft and its suppliers provide the Specification (and all intellectual property therein) and any (if any) support services related to the Specification ("Support Services") AS IS AND WITH ALL FAULTS, and hereby disclaim all warranties and conditions, either express, implied or statutory, including, but not limited to, any (if any) implied warranties or conditions of merchantability, of fitness for a particular purpose, of lack of viruses, of accuracy or completeness of responses, of results, and of lack of negligence or lack of workmanlike effort, all with regard to the Specification, any intellectual property therein and the provision of or failure to provide Support Services. ALSO, THERE IS NO WARRANTY OR CONDITION OF TITLE, QUIET ENJOYMENT, QUIET POSSESSION, CORRESPONDENCE TO DESCRIPTION OR NON-INFRINGEMENT, WITH REGARD TO THE SPECIFICATION AND ANY INTELLECTUAL PROPERTY THEREIN. THE ENTIRE RISK AS TO THE QUALITY OF OR ARISING OUT OF USE OR PERFORMANCE OF THE SPECIFICATION, ANY INTELLECTUAL PROPERTY THEREIN, AND SUPPORT SERVICES, IF ANY, REMAINS WITH YOU.

5. EXCLUSION OF INCIDENTAL, CONSEQUENTIAL AND CERTAIN OTHER DAMAGES. To the maximum extent permitted by applicable law, in no event shall Microsoft or its suppliers be liable for any special, incidental, indirect, or consequential damages whatsoever (including, but not limited to, damages for loss of profits or confidential or other information, for business interruption, for personal injury, for loss of privacy, for failure to meet any duty including of good faith or of reasonable care, for negligence, and for any other pecuniary or other loss whatsoever) arising out of or in any way related to the use of or inability to use the SPECIFICATION, ANY INTELLECTUAL PROPERTY THEREIN, the provision of or failure to provide Support Services, or otherwise under or in connection with any provision of this AGREEMENT, even in the event of the fault, tort (including negligence), strict liability, breach of contract or breach of warranty of Microsoft or any supplier, and even if Microsoft or any supplier has been advised of the possibility of such damages.

6. LIMITATION OF LIABILITY AND REMEDIES. Notwithstanding any damages that you might incur for any reason whatsoever (including, without limitation, all damages referenced above and all direct or general damages), the entire liability of Microsoft and any of its suppliers under any provision of this Agreement and your exclusive remedy for all of the foregoing shall be limited to the greater of the amount actually paid by you for the Specification or U.S.$5.00. The foregoing limitations, exclusions and disclaimers shall apply to the maximum extent permitted by applicable law, even if any remedy fails its essential purpose.

7. APPLICABLE LAW. If you acquired this Specification in the United States, this Agreement is governed by the laws of the State of Washington. In respect of any dispute which may arise hereunder, you consent to the jurisdiction of the state and federal courts sitting in King County, Washington.

8. ENTIRE AGREEMENT. This Agreement is the entire agreement between you and Microsoft relating to the Specification supersedes all prior or contemporaneous oral or written communications, proposals and representations with respect to the Specification or any other subject matter covered by this Agreement. To the extent the terms of any Microsoft policies or programs for Support Services conflict with the terms of this Agreement, the terms of this Agreement shall control.


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