User Time is the percentage of processor time spent in User Mode in non-Idle threads. All application code and subsystem code execute in User Mode. The graphics engine, graphics device drivers, printer device drivers, and the window manager also execute in User Mode. Code executing in User Mode cannot damage the integrity of the Windows NT Executive, Kernel, and device drivers. 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.