From a high-level perspective, each version of Windows XP was exactly the same no matter what hardware it ran on. Yes, the set of device drivers running on each system could be vastly different, but from the user's perspective, it didn't matter whether you were running a bare-bones budget PC or a 64-bit behemoth: The look and feel of XP, and the programs and features that were available, didn't change.

On the surface, that seems more than a little strange because there's a huge performance gulf between a box that meets only the minimal requirements for running Windows and a top-end machine with a fast 64-bit processor, scads of RAM, and a state-of-the-art GPU. Unfortunately, this situation meant that all too often the system opted for lowest-common-denominator settings that worked for low-end machines but did nothing to take advantage of high-end hardware.

Fortunately, this one-size-fits-all approach to Windows will be history after Windows Vista ships. That's because Vista tailors certain aspects of itself depending on the capabilities of the system on which it's installed. Vista interface will change depending on the graphics hardware on the machine, with low-end machines getting the straightforward Classic interface, midrange adapters getting the regular Aero theme, and high-end GPUs getting the full Aero Glass treatment.

But Vista also scales other aspects up or down to suit its hardware home. With games, for example, Vista enables certain features only if the hardware can support them. Other features that are scaled for the computer's hardware are TV recording (for example, how many channels can be recorded at once?) and video playback (for example, what is the optimal playback size and frame rate that doesn't result in dropped frames?).

The tool that handles all of this not only for Vista itself, but also for third-party programs, is the Windows System Assessment Tool, or WinSAT. This tool runs during setup and whenever you make major performance-related hardware changes to your system. It focuses on four aspects of your system performance: graphics, memory, processor, and storage. For each of these subsystems, WinSAT maintains a set of metrics stored as an assessment in XML format.

Vista then needs to examine only the latest assessment to see what features the computer can support. Note, too, that third-party programs can use an application programming interface that gives them access to the assessments, so developers can tune program features depending on the WinSAT metrics.

Five metrics are used:

• Processor - This metric determines how fast the system can process data. The Processor metric is measured in megabytes per second processed.
• Memory (RAM) - This metric determines how quickly the system can move large objects through memory. The Memory metric is measured in megabytes per second.
• Primary hard disk - This metric determines how fast the computer can write to and read from the hard disk. The Storage metric is measured in megabytes per second.
• Graphics - This metric determines the computer's capability to run a composited desktop like the one created by the Desktop Window Manager. The Graphics metric is expressed in frames per second.
• Gaming Graphics - This metric determines the computer's capability to render 3D graphics, particularly those used in gaming. The Gaming Graphics metric is expressed in effective frames per second.