| Socks |
04-24-2008 08:20 PM |
In Windows NT operating systems, the System Idle Process is a kernel thread, which runs when no other runnable thread can be scheduled on a CPU. For example, there may be no runnable thread in the system, or all runnable threads are already running on a different CPU.
The System Idle Process is used by Windows NT to implement CPU power saving. The exact power saving scheme depends on the hardware and firmware capabilities of the system in question. For instance, on x86 processors, the process will run a loop of HLT instructions, which causes the CPU to turn off many internal components and wait until an IRQ arrives.
The CPU time consumed by the System Idle Process is commonly of interest for end users, as it is a measure of the CPU utilization in their system which is easily accessible through Windows' Task Manager program. There are, however, more detailed sources of such information available through Windows' performance monitoring system (accessible with the perfmon program), which includes more finely grained categorization of CPU time spending. A limited subset of the CPU time categorization is also accessible through the Task Manager, which can display CPU usage by CPU, and categorized by time spent in user vs. kernel code. It should be noted, though, that that information is not calculated from information about the System Idle Process, but from the system's global performance counters.
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