Windows NT allows you to measure many aspects of its performance and status. This performance data is collected in the Windows NT registry and can be displayed using the Windows NT Performance Monitor (PERFMON.EXE).
The extensible performance counter interface allows applications, drivers, and services to add performance data to the registry, using an extensible performance counter DLL. This performance data can be displayed in Performance Monitor, along with the system performance data. The EXCTRLST utility uses the registry to find the applications, drivers, and services that have registered an extensible performance counter DLL.
For more information, see Performance Data Helper.