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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 ...
Running a processor at high clock speeds allows for better performance. However, when the same processor is run at a lower frequency (speed), it generates less heat and consumes less power. In many cases, the core voltage can also be reduced, further reducing power consumption and heat generation. By using SpeedStep, users can select the ...
ACPI 1.0 (1996) defines a way for a CPU to go to idle "C states", but defines no frequency-scaling system. ACPI 2.0 (2000) introduces a system of P states (power-performance states) that a processor can use to communicate its possible frequency–power settings to the OS. The operating system then sets the speed as needed by switching between ...
The same is true for newer processors: When a single-core Intel CPU was 20% underclocked, the PC's performance was down only 13% with a 49% power reduction. [3] In general, the power consumed by a CPU with a capacitance C, running at frequency f and voltage V is approximately [4] =.
In PCs, the CPU's external address and data buses connect the CPU to the rest of the system via the "northbridge". Nearly every desktop CPU produced since the introduction of the 486DX2 in 1992 has employed a clock multiplier to run its internal logic at a higher frequency than its external bus, but still remain synchronous with it. This ...
This involves comparing the timer tick of the operating system (the tick that usually is 100–1000 times per second) and the speed of the CPU. 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.
Typically, the CPU time used by a program is measured by the operating system, which schedules all of the work of the CPU. Modern multitasking operating systems run hundreds of processes. (A process is a running program.) Upon starting a process, the operating system records the time using an internal timer.
The feature was relatively common on systems running 286 to 486 CPUs, [7] and less common on Pentium era computers. The frequency displays largely disappeared or were reprogrammed to display "HI"/"LO", "99", or were replaced with a three-digit display when CPU speeds reached 100 MHz, since most systems only had a two-digit display.