A. When you install Vista, a score is calculated that evaluates the computer's performance based on five areas: processor, memory, graphics, gaming graphics, and hard disk. Each of these elements has a score, with the lowest of all the scores making your machine's "base score" as the figure shows. Because my gaming graphics score was only 3, my machine's base score is 3, even though all the other elements scored much higher.
If something changes in your machine (e.g., hardware or a newer driver) you can perform a test by clicking the "Update my score" button, which you'll find under the performance score results. This score is also shown on the Games Explorer interface, which shows what a game requires to function. The "Update my score" button calls the Windows System Assessment Tool (Winsat.exe), which runs the tests to calculate the performance scores.