Microsoft KB Archive/189803

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PRB: PMPI FanThrottleToleranceAc/Dc Not Implemented Under Win98

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Q189803

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The information in this article applies to:


 * Microsoft Win32 Software Development Kit (SDK), on platform(s):
 * Microsoft Windows 98

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SYMPTOMS
The FanThrottleToleranceAc and FanThrottleToleranceDc members, which are defined as part of the Power Management Profile Interface (PMPI), are not implemented on Windows 98.

CAUSE
Windows 98 does not implement support for passive cooling mode, which is required to support the FanThrottleToleranceAc/Dc functionality.

STATUS
Microsoft has confirmed this to be a problem in Windows 98.

MORE INFORMATION
FanThrottleToleranceAc and FanThrottleToleranceDc are defined as members of the USER_POWER_POLICY structure in the "Windows Power Management Configuration Tools Design Notes and Reference" white paper, Version 1.0, published May 1, 1998 by Microsoft. In this document, the following functionality is described:

FanThrottleToleranceAc/Dc When the system is running on AC/battery power, the lowest acceptable relative speed at which to run any processor, in order to prevent a fan from coming on. A value of 80 would mean it is acceptable to reduce processor speed down to 80 percent of optimum speed for the purposes of keeping the fan off. A value of 100 indicates that the processor performance is more important than the fan. Any value other than 100 indicates that the preference is to slow the processor as allowed before running the fan. Range: 0-100.

However, regardless of the value of FanThrottleToleranceAc/Dc, the CPU is never throttled prior to turning on the fan for cooling.