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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.
The final result comes from dividing the number of instructions by the number of CPU clock cycles. The number of instructions per second and floating point operations per second for a processor can be derived by multiplying the number of instructions per cycle with the clock rate (cycles per second given in Hertz) of the processor in question ...
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.
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.
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 ...
Seymour Cray's CDC 6600 from 1964 is often mentioned as the first superscalar design. The 1967 IBM System/360 Model 91 was another superscalar mainframe. The Intel i960CA (1989), [3] the AMD 29000-series 29050 (1990), and the Motorola MC88110 (1991), [4] microprocessors were the first commercial single-chip superscalar microprocessors.
An early example is the “Dual CPU” version of the four-bit COP400 that was introduced by National Semiconductor in 1981. This single-chip microcontroller contains two ostensibly independent CPUs that share instructions, memory, and most IO devices. In reality, the dual CPUs are a single two-thread barrel processor.
If the OS timer and the CPU run on two independent clock crystals the situation is ideal and more or less the same as the previous example. But even if they both use the same clock crystal the process /program that does the clock drift measurement is "disturbed" by many more or less unpredictable events in the CPU such as interrupts and other ...