Microsoft debuted its Windows Experience Index (WEI) tool in Windows Vista as a way to measure the relative performance of the components in your PC. As such, each key hardware device in the PC, including the microprocessor, RAM, graphics (for the UI and for more advanced tasks), and hard disk, is assessed and awarded a sub-score; and the lowest scoring component is used as the basis for the system's overall WEI score. In general, a higher-scoring PC will perform better, overall, than a lower-scoring PC. Likewise, a higher-scoring component on one PC likely performs better than a lower-scoring component on a second PC.

In Microsoft's bizarre rating system, components can achieve a score of between 1.0 and 7.9. In Windows Vista, this range extended only to 5.9, but Microsoft says it has increased the range due to the evolution of hardware capabilities in the time since Windows Vista was released. Equally bizarre, Microsoft has actually changed how it rates hardware since Windows Vista, so identical hardware components could actually receive different subscores on each OS, making Vista-to-Windows 7 comparisons impossible.

Fun fact: Microsoft's changing of the WEI score range to 7.9 is akin to Spinal Tap's Nigel changing his amp's volume level to extend to 11. "Why don't you just make 10 louder and make 10 be the top number, and make that a little louder?," director Marty DiBergi asks Nigel in the classic movie "This is Spinal Tap." "These go to 11," Nigel insists, after mulling it over. Exactly.

Testing your PC

As with Windows Vista, Windows 7 undergoes a hardware performance test during the final phases of Setup. Unlike with Windows Vista, however, the Windows 7 performance test is not lengthy and does not hold up Setup for an unacceptable amount of time. Regardless, you will almost certainly have to manually re-run the performance test after first installing Windows 7, as any hardware changes--including post-Setup driver installs--will reset the system's findings.

To manually re-run the WEI performance test, you will need to follow a circuituitous route to the tool. Open the Start Menu, right-click on Computer, and choose Properties. Then, in the System window, click the link next to Rating. It will read, "Your Windows Experience Index needs to be refreshed," "System rating unavailable," or "Windows Experience Index," depending on the status of the test. When you do so, the Performance Information and Tools window appears.

Windows 7 Feature Focus: WEI
Performance Information and Tools provides your WEI score.

Tip: You can access this tool more quickly using Start Menu Search: Open the Start Menu and type performance and then select Performance Information and Tools from the search results that appear.

If you need to re-run the test, a prominent Refresh Now button will be present near the top right of the window. Otherwise, you can click the link titled "Re-run the assessment" in the bottom right of the window. The test takes a few minutes and you should leave your PC alone during this time.

Understanding the score and sub-scores

As noted previously the Windows Experience Index tests five key hardware components in your PC. These include:

Processor. This is the microprocessor at the heart of your PC. WEI tests the number of calculations the processor can make per second.

Memory (RAM). This is the random access memory that stores the operating system and applications at run-time. WEI tests the memory operations this hardware can perform per second.

Graphics. WEI breaks down the graphical capabilities of your system into two separate sub-scores. This first sub-score is for desktop performance, specifically that of the Windows Aero user experience.

Gaming graphics. The second graphics-based subscore, contrary to its name, is actually for 3D business and gaming graphics performance.

Primary hard disk. The final subscore measures the data transfer rate of the system's primary hard disk; i.e. the disk on which Windows (and, presumably, your applications) is installed.

Each component is assessed a subscore. The lowest subscore is used as your system's base score, or "score."

Secret: Why isn't the WEI score not an average score of the component subscores instead? Microsoft feels that a PC can perform only as well as the weakest link in the system. I think they have a point.

One of the problems with the WEI is that it's largely arbitrary. You may be distressed by the low scores of some components and believe that you require an upgrade to run Windows 7 effectively. However, this is rarely the case. On my desktop system, which features a massively performant quad-core microprocessor (with a WEI subscore of 7.1) and a whopping 8 GB of RAM, the overall base score is just 3.3 because I never upgraded the integrated graphics in the system. But I don't play video games on this PC and the graphics hardware is more than adequate for Aero and the work I do each day. In fact, this system runs rings around any PC I've ever used.

You may also be surprised to discover that upgrading certain components doesn't change the WEI base score, or specific subscores, by much if it all. For example, upgrading the RAM on a ThinkPad laptop recently raised the Memory (RAM) subscore by only a few tenths of a point. And it didn't raise the base score at all, since the RAM wasn't the lowest-scoring component. On the other hand, upgrading from integrated graphics to a dedicated 3D graphics card--even a very inexpensive one--should provide dramatic bumps to the two graphics subscores.

Another issue with the WEI is that, because it runs only once and while you are not actually using the PC, it doesn't provide a meaningful measurement of the performance capabilities of your system over time. (Instead, you can use the hugely useful Reliability Monitor--see my Windows Vista Feature Focus for more information).

Put simply, WEI does not measure the overall performance of your PC. It only measures the relative performance of the individual hardware components in the PC.

Given this, what's the point of WEI? According to Microsoft, WEI is all about how the hardware components in the PC interact with Windows 7. So while a lower base score is obviously "worse" than a higher base score, what this number really measures is how and whether the PC's components enable certain Windows features. Microsoft provides the following information about interpreting a computers base score:

1.0 to 1.9 - Basic performance. Even a component with a 1.0 subscore meets the Windows 7 minimum requirements.

2.0 to 2.9 - Enhanced performance. Windows Aero may be available.

3.0 to 3.9 - Windows Aero will be enabled.

4.0 to 4.9 - Good performance with high-resolution displays and multiple displays.

5.0 to 5.9 - Capable of running high-end video games, 3D modeling applications, and high-end video editing applications.

6.0 to 6.9 - Supports DirectX 10 graphics with high frame rates at high resolutions.

7.0 to 7.9 - Highest performance level available. Reserved for systems with SSD hard drive, high-end graphics card, and multi-core (i.e. 8 or more) processor.

Secret: Still not convinced that the WEI subscores and score are essentially meaningless? Well consider this: They can easily be faked. That's right. Now we can all go to 11!

Final thoughts

When the Windows Experience Index appeared in Windows Vista, it seemed designed specifically to reassure consumers who were worried about the supposedly heady hardware requirements of the then-new OS. Today, there isn't a PC being sold that can't run Windows Aero (including all low-end netbooks), and of course Windows 7 runs better on lower-end hardware than does Windows Vista. It's hard to understand, then, what the point is of continuing to measure relative hardware performance when the provided scores don't, in fact, relay any meaningful information about the performance of your PC. When you couple this with the removal of some tools that would be quite helpful for measuring and changing PC performance--the Software Explorer from Windows Defender come immediately to mind--the continuation of Windows Experience Index in Windows 7 is all the more confusing. That Microsoft has actually spent time arbitrarily updating the scoring system is even more curious.

Forced to guess, it appears that WEI is actually designed primarily as a tool for Microsoft to obtain valuable data about the hardware on which Windows is run. It offers only negligible value to consumers, and has likely caused more than a few unnecessary hardware upgrades.