What is WEI (Windows Experience Index) Score in Windows 7 OS ?

Windows Experience Index (WEI) is common way to measure and express the capabilities of a computer's hardware and software configuration.
Windows Experience Index or WEI is displayed as a number named as base score.
High values in WEI means high performance, speed and more enhanced system which results your operating system to perform difficult task easier and enables some resource intensive components on your computer like Aero features.

For Windows 7 installed OS, the Windows Experience Index (WEI) score changes between 1.0 and 7.9 according to your installed computer's hardware and software configuration properties.
Windows Experience Index or WEI is calculated for each individual core components of your computer and OS. And the overall WEI base score is determined by the lowest score of all components.

In order to display Windows Experience Index (WEI) score of your Windows 7 or Windows Vista operating system running PC;
open "Control Panel > System and Security > Action Center" menu.
Then among left side links, click on View Performance Information link.
This will display the Windows 7 Performance Information and Tools screen.
You can see your Windows 7 PC or Windows Vista PC WEI score (Windows Experience Index) on the right as seen in the following screenshot.

If your base score is outdated then you can recalculate your WEI by "Re-run the assessment" link buton.