Idle (CPU)

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A computer processor is described as idle when it is not being used by any program.


On processors that have a halt instruction that stops the CPU until an interrupt occurs, such as x86's HLT instruction, it may save significant amounts of power and heat if the idle task consists of a loop which repeatedly executes HLT instructions.

Most operating systems[which?] will display an idle task, which is a special task loaded by the OS scheduler only when there is nothing for the computer to do. The idle task can be hard-coded into the scheduler, or it can be implemented as a separate task with the lowest possible priority. An advantage of the latter approach is that programs monitoring the system status can see the idle task along with all other tasks;[citation needed] an example is Windows NT's System Idle Process.


Some programs are designed to make use of CPU Idle Time, meaning that they run at a low priority so as not to impact programs that run at normal priority. This allows non-crucial background programs to only run when it would not affect the performance of other applications. Programs like this may cause the CPU to be at 100% utilization all the time which causes the CPU to consume more power, since most modern CPUs can enter power-save modes when they are completely idle.

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