IBM THINKPAD G40 Series Service And Troubleshooting Manual page 51

Solving computer problems
Solution: This problem may occur when the ac adapter is not attached. To
prolong battery life with the higher frequency of Intel's Pentium 4/Celeron
processors, the ThinkPad G40 implements the Dynamic CPU Throttling
feature, which reduces CPU frequency dynamically: 1) when the system
operates in battery mode; 2) when the system increases power consumption;
3) when system temperature increases.
To avoid or reduce this problem, do one or all of the following:
1. Attach the ac adapter.
2. Close applications not being used.
3. Try to lower system temperature by increasing the fan speed with the
Battery MaxiMiser Wizard with Fan Control.
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Chapter 2. Solving computer problems