Q: Under Vista Ultimate, my computer earned a Windows Experience Index of 5.9. (I expected that because I own a Dell Precision M6400 mobile workstation that’s maxed out in performance. When I did an upgrade install of Windows 7 RC (Build 7100), I was disappointed to see the Performance Experience Index remain at 5.9. I thought it would increase to 7.9. Is there a problem with Windows 7 RC on an upgrade install?

A: First, a little background. Microsoft introduced the Windows Experience Index with Windows Vista. It’s a number that lets shoppers see how PCs matches up against each other in terms of speed, memory, processing power, and graphics. To see your PC’s Windows Experience Index, click the Start button, right-click Computer and choose Properties. By comparing numbers on the showroom floor, shoppers can more easily see the strengths and weaknesses of different PCs.

The Windows Experience Index shown to the left lists this PC as rating 4.4. In Windows Vista, PCs ranked anywhere from 1.0 to 5.9, and your PC ranked at the top. However, Microsoft changed the rankings with Windows 7, ranking PCs on a scale between 1.0 and 7.9.

Although your PC ranked tops on Windows Vista’s scale, several things could be responsible for it not reaching the top of Windows 7’s scale:

• Drivers. Manufacturers tweak their drivers with each release of Windows, and it’s possible one of your PC’s parts is still using a beta driver. When a newer driver arrives that’s optimized for Windows 7, your PC might earn a higher score.
• Laptop. Your PC may be top-of-the line, but it’s a laptop, and laptops can never compete with top-of-the-line PCs. Today’s more powerful desktop PCs might have nudged your laptop out of the top ranks and into a slightly lower ranking.
• Age. Microsoft designed the Windows Experience Index to change constantly over the years, adjusting for newer PCs and their faster performance. What ranked at the top of the scale last year probably won’t rank at the top of the scale in Windows 7.

So, although the difference in scores could lie with a beta driver, the ranking probably stems from your laptop being about a year old. It’s a workhorse, no doubt, but it’s no longer as powerful as the PCs hitting today’s market.