The browser power meter displays the minimum setTimeout callback interval which indicates the browsers impact on power consumption. The shorter the interval, the less time the CPU can enter longer sleep states therefore consuming more power and impacting battery life.
The web platform allows for periodic callbacks via window.setTimeout() and window.setInterval(). In order to achieve small minimum timeouts on Windows Vista and Windows 7, browser vendors decrease the System Timer Resolution from the default 15.6ms which comes at the cost of power consumption. From Timers, Timer Resolution, and Development of Efficient Code June 16, 2010 Page 3: The default timer resolution on Windows 7 is 15.6 milliseconds (ms). Some applications reduce this to 1 ms, which reduces the battery run time on mobile systems by as much as 25 percent. The increased power consumption also impacts desktop computers resulting in higher energy costs and greater environmental impact.
Internet Explorer 9 RC is aware of the user's power profile and by default does not lower the System Timer Resolution when running on battery. You can see the difference by plugging and unplugging your laptop power cord to watch the above power meter change when the browser change. Please run only one browser at a time when using this demo.
If you would like to explore timer resolutions further, you can run ClockRes to display the current System Timer Resolution and see when and how different browsers change it. You can also run the command "powercfg /energy" from the Windows command line as described in Using PowerCfg to Evaluate System Energy Efficiency to list applications that impact System Timer Resolution.