Privileged Time is the percentage of processor time spent in Privileged Mode in non-Idle threads. The Windows NT service layer, the Executive routines, and the Windows NT Kernel execute in Privileged Mode. Device drivers for most devices other than graphics adapters and printers also execute in Privileged Mode. Unlike some early operating systems, Windows NT uses process boundaries for subsystem protection in addition to the traditional protection of User and Privileged modes. These subsystem processes provide additional protection. Therefore, some work done by Windows NT on behalf of your application may appear in other subsystem processes in addition to the Privileged Time in your process.