Why did my Windows Experience Index rating change?
The range of ratings for the Windows Experience Index has been increased to 7.9, but in some cases you might notice that ratings for the same hardware have gone down when compared to older versions of Windows. That's because the Windows Experience Index has added some new tests that measure more factors when assessing your computer’s performance. Even though your rating has gone down, you might not see any decrease in actual performance. For more information, see What is the Windows Experience Index?