Every program or task that runs on a computer system occupies a certain amount of processing time on the CPU.
Common methods are reducing the clock speed along with the CPU voltage and sending parts of the processor into a sleep state.
Many operating systems, for example Windows,[1] Linux,[2] and macOS[3] will run an idle task, which is a special task loaded by the OS scheduler on a CPU when there is nothing for the CPU to do.
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.
This allows non-crucial background programs to only run when it would not affect the performance of other applications.