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The dynamic power (switching power) dissipated by a chip is C·V 2 ·A·f, where C is the capacitance being switched per clock cycle, V is voltage, A is the Activity Factor [1] indicating the average number of switching events per clock cycle by the transistors in the chip (as a unitless quantity) and f is the clock frequency. [2]
In 2006, a side channel attack was published [5] that exploited clock skew based on CPU heating. The attacker causes heavy CPU load on a pseudonymous server (Tor hidden service), causing CPU heating. CPU heating is correlated with clock skew, which can be detected by observing timestamps (under the server's real identity).
Power consumption due to leakage power emanates at a micro-level in transistors. Small amounts of currents are always flowing between the differently doped parts of the transistor. The magnitude of these currents depend on the state of the transistor, its dimensions, physical properties and sometimes temperature.
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 ...
Constant TSC behavior ensures that the duration of each clock tick is uniform and makes it possible to use the TSC as a wall-clock timer even if the processor core changes frequency. This is the architectural behavior for all later Intel processors. AMD processors up to the K8 core always incremented the time-stamp counter every clock cycle. [6]
TM2 reduces processor temperature by lowering the CPU clock multiplier, and thereby the processor core speed. [2] In contrast, Thermal Monitor 1 inserts an idle cycle into the CPU for thermal control without decreasing multipliers. TM1 and TM2 are associated with DTS/PECI — Digital Temperature Sensor/Platform Environment Control Interface. [3]
The purpose of overclocking is to increase the operating speed of a given component. [3] Normally, on modern systems, the target of overclocking is increasing the performance of a major chip or subsystem, such as the main processor or graphics controller, but other components, such as system memory or system buses (generally on the motherboard), are commonly involved.
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.