Intel SpeedStep Technology

Intel SpeedStep Technology allows you to customize the clock frequency on your notebook.When the notebook is plugged into the AC power the processor will run in Maximum Performance mode. When you unplugged your notebook from the power outlet & running on batteries, the processors would switch to a low frequency or low performance mode.So, the notebook will run in Battery Optimized performance mode.
The low frequency use less electrical power and the battery life could be increased.
If you wish you can change the settings in BIOS or in Power options under control panel.

Enhanced SpeedStep Technology
SpeedStep Technology was introduced by Intel for the bigger concern of battery life in notebook computers.Later Intel came up with Enhanced SpeedStep Technology.
Enhanced SpeedStep Technology switch between a low frequency to high frequency state as needed by the application.

Windows XP Power Schema
In Windows XP, you can access the power profiles by going to Control Panel -> Power Options -> Power Schemes. There are different power shemas available. Based on your need you can select the right one. Even you can have your own power schema and save it.You can find the Windows XP built in shemas in the below table.

Built In Schemas	Behavior
Home/Office Desk	Plugged Behavior Highest Performance State. Unplugged Behavior Switch Performance State based on need.
Portable/Laptop	Plugged Behavior Switch Performance State based on need. Unplugged Behavior Switch Performance State based on need.
Presentation	Plugged Behavior Switch Performance State based on need. Unplugged Behavior Lowest Performance State.
Always On	Plugged Behavior Highest Performance State. Unplugged Behavior Highest Performance State.
Minimal Power Management	Plugged Behavior Switch Performance State based on need. Unplugged Behavior Switch Performance State based on need.
Max Battery	Plugged Behavior Switch Performance State based on need. Unplugged Behavior Lowest Performance State.

Try to check the frequency switch in your laptop with & w/o power. Don't run any application so that you can see the difference. Start - My computer - Properties -( processor frequency which is in MHZ)