You can use the performance data provided by applications, services, and drivers to determine system bottlenecks and fine-tune system and application performance. The easiest way to display the performance data is to use the Performance Monitor application located in the Administrative Tools group.
If you need to collect performance data for your application, the easiest way to do this is to use the interface provided by the Performance Data Helper (PDH) interface. Applications that need more control over performance data collection can use the registry interface directly. This is the method that is used by the functions in PDH.DLL and by the Performance Monitor. It is more efficient for the Performance Monitor to use the registry interface, because it displays counters grouped by object. If you are retrieving individual counters, rather than a group of counters from a particular object, it is just as efficient to use the PDH interface.
This overview discusses both interfaces.
In addition, this overview discusses how to add your own performance counters, by creating an extensible performance DLL. For more information, see Adding Performance Counters.