Task Manager may not calculate CPU usage correctly on Windows 2000, Windows Server 2003, or Windows XP


When you view the Processes tab in Task Manager, you notice that the sum of the CPU value for the System Idle Process object and the CPU Usage value that is reported in the status bar may be more than 100 percent. Sometimes the sum may be more than 140 percent.

Note The System Idle Process indicates the unused percentage of the CPU.


This issue occurs because Task Manager does not associate deferred procedure calls (DPCs) or interrupts with the processes that request them. This can cause CPU Usage and System Idle Process calculations that are not correct.


To monitor CPU performance more accurately, use System Monitor. To do this, follow these steps:
  1. Click Start, click Run, type perfmon, and then click OK.
  2. In Performance, click the New Counter Set button in the details pane.

    Note Move the pointer over the buttons in the details pane to find the New Counter Set button.
  3. Click the Add button.
  4. In Select counters from list, click %Processor Time, and then click Add.
  5. In Select counters from list, click %Idle Time, and then click Add.
  6. Click Close.
  7. Click the View Report button.


For related information, view the topics that are listed in the following Help and Support content.
  • Windows Server 2003: "Monitoring server performance" topic in Windows Server 2003 Help and Support.
  • Windows XP: "Using Performance" topic in Windows XP Help and Support.
  • Windows 2000: "Monitoring performance" in Windows 2000 Help.