Select the product you need help with
- Internet Explorer
- Windows Phone
- More products
The Laptop Computer May Be Unable to Enter the C3 Processor Power-Saving State
Article ID: 297045 - View products that this article applies to.
This article was previously published under Q297045
Your laptop computer may be unable to enter the C3 processor power-saving state.
This problem can occur because the active bus polling that is required to maintain communication with universal serial bus (USB) devices can prevent the CPU from switching to a C3 power-saving state. By default, the USB polling interval is set for every one millisecond (ms). Even if no devices are connected to the USB controller, the polling operation is still performed and the processor cannot enter a C3 power-saving state.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/322756/ )How to back up and restore the registry in Windows
To resolve this problem, increase the USB polling interval from one ms to five ms. Then, the processor can enter a C3 power-saving state during its inactivity and extend the battery life of the computer. To increase this polling interval, add a registry entry that is dependent upon the operating system:
For Windows Millennium Edition
For Windows 2000
Battery-powered computers that use Advanced Power Management (APM) or Advanced Configuration and Power Interface (ACPI) may experience increased power consumption leading to a more rapid drain of battery power. This type of problem only occurs on computers that use an OHCI USB controller.
Note If you use Windows Vista, you can visit the following Microsoft Web page for help with power consumption and battery life problems:
Fix problems in which power consumption is more than expected or the battery life is short