Idle (CPU)
Encyclopedia
A computer processor is described as idle when it is not being used by any program
.
Programs which make use of CPU Idle Time mean that they run at a low priority so as not to impact programs that run at normal priority. Many programs that use CPU idle time cause the CPU to always be 100% utilized, so that the time spent where the CPU would have been idle is instead spent performing useful computations. This generally causes the CPU to consume more power as most modern CPUs can enter power-save modes when they are idle. On modern processors, where a HLT
(halt) instruction saves significant amounts of power and heat, the idle task almost always consists of a loop which repeatedly executes HLT instructions.
Most operating systems 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; an example is Windows NT
's System idle process
.
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
.
Programs which make use of CPU Idle Time mean that they run at a low priority so as not to impact programs that run at normal priority. Many programs that use CPU idle time cause the CPU to always be 100% utilized, so that the time spent where the CPU would have been idle is instead spent performing useful computations. This generally causes the CPU to consume more power as most modern CPUs can enter power-save modes when they are idle. On modern processors, where a HLT
HLT
In the x86 computer architecture, HLT is an assembly language instruction which halts the CPU until the next external interrupt is fired. Such interrupts are used by devices in order to signal to the CPU that an event occurred which the CPU shall react on...
(halt) instruction saves significant amounts of power and heat, the idle task almost always consists of a loop which repeatedly executes HLT instructions.
Most operating systems will display an idle task, which is a special task loaded by the OS scheduler
Scheduling (computing)
In computer science, a scheduling is the method by which threads, processes or data flows are given access to system resources . This is usually done to load balance a system effectively or achieve a target quality of service...
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; an example is Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
's System idle process
System idle process
In Windows NT operating systems, the System Idle Process contains one or more kernel threads which run 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...
.