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Its CPU time "usage" is a measure of how much CPU time is not being used by other threads. In Windows 2000 and later the threads in the System Idle Process are also used to implement CPU power saving. The exact power saving scheme depends on the operating system version and on the hardware and firmware capabilities of the system in question ...
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. The idle task can be hard-coded into the scheduler, or it can be implemented as a separate task with the lowest possible priority.
FreeBSD uses a multilevel feedback queue with priorities ranging from 0–255. 0–63 are reserved for interrupts, 64–127 for the top half of the kernel, 128–159 for real-time user threads, 160–223 for time-shared user threads, and 224–255 for idle user threads. Also, like Linux, it uses the active queue setup, but it also has an idle ...
CPU time (or process time) is the amount of time that a central processing unit (CPU) was used for processing instructions of a computer program or operating system. CPU time is measured in clock ticks or seconds. Sometimes it is useful to convert CPU time into a percentage of the CPU capacity, giving the CPU usage.
The CPU-bound process will get and hold the CPU. During this time, all the other processes will finish their I/O and will move into the ready queue, waiting for the CPU. While the processes wait in the ready queue, the I/O devices are idle. Eventually, the CPU-bound process finishes its CPU burst and moves to an I/O device.
On the other hand, if a new user starts a process on the system, the scheduler will reapportion the available CPU cycles such that each user gets 20% of the whole (100% / 5 = 20%). Another layer of abstraction allows us to partition users into groups, and apply the fair share algorithm to the groups as well.
The concept of CPU-bounding was developed during early computers, when data paths between computer components were simpler, and it was possible to visually see one component working while another was idle. Example components were CPU, tape drives, hard disks, card-readers, and printers.
For example, an IBM PC with an Intel 80486 CPU running at 50 MHz will be about twice as fast (internally only) as one with the same CPU and memory running at 25 MHz, while the same will not be true for MIPS R4000 running at the same clock rate as the two are different processors that implement different architectures and microarchitectures ...