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Idle is a state that a computer processor is in when it is not being used by any program. Every program or task that runs on a computer system occupies a certain amount of processing time on the CPU. If the CPU has completed all tasks it is idle. Modern processors use idle time to save power.
In multiprocessor computer systems, software lockout is the issue of performance degradation due to the idle wait times spent by the CPUs in kernel-level critical sections. Software lockout is the major cause of scalability degradation in a multiprocessor system, posing a limit on the maximum useful number of processors.
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. In a multiprocessor system, there is one idle thread associated with each CPU core. For a system with hyperthreading enabled, there is an idle thread for each logical processor.
An idle computer has a load number of 0 (the idle process is not counted). Each process using or waiting for CPU (the ready queue or run queue) increments the load number by 1. Each process that terminates decrements it by 1. Most UNIX systems count only processes in the running (on CPU) or runnable (waiting for CPU) states.
typical thermal power, which is measured under normal load (for instance, AMD's average CPU power) maximum thermal power, which is measured under a worst-case load; For example, the Pentium 4 2.8 GHz has a 68.4 W typical thermal power and 85 W maximum thermal power. When the CPU is idle, it will draw far less than the typical thermal power.
The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch–execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
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 ...