% DPC Time - The percentage of elapsed time that the Processor spent in Deferred Procedure Calls (DPC). When a hardware device interrupts the Processor, the Interrupt Handler may elect to execute the majority of its work in a DPC. DPCs run at lower priority than Interrupts. This counter can help determine the source of excessive time being spent in Privileged Mode.
% Interrupt Time - The percentage of elapsed time that the Processor spent handling hardware Interrupts. When a hardware device interrupts the Processor, the Interrupt Handler will execute to handle the condition, usually by signaling I/O completion and possibly issuing another pending I/O request. Some of this work may be done in a DPC (see % DPC Time.)
% Privileged Time - 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,
% Processor Time - Processor Time is expressed as a percentage of the elapsed time that a processor is busy executing a non-idle thread. It can be viewed as the fraction of the time spent doing useful work. Each processor is assigned an idle thread in the idle process that consumes those unproductive processor cycles not used by any other threads.
% User Time - 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.