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In computing, the clock multiplier (or CPU multiplier or bus/core ratio) sets the ratio of an internal CPU clock rate to the externally supplied clock. This may be implemented with phase-locked loop (PLL) frequency multiplier circuitry. A CPU with a 10x multiplier will thus see 10 internal cycles for every external clock cycle. For example, a ...
Common methods are reducing the clock speed along with the CPU voltage and sending parts of the processor into a sleep state. On processors that have a halt instruction that stops the CPU until an interrupt occurs, such as x86 's HLT instruction, it may save significant amounts of power and heat if the idle task consists of a loop which ...
Clock rate or clock speed in computing typically refers to the frequency at which the clock generator of a processor can generate pulses used to synchronize the operations of its components. [1] It is used as an indicator of the processor's speed. Clock rate is measured in the SI unit of frequency hertz (Hz).
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).
Instructions per second (IPS) is a measure of a computer's processor speed. For complex instruction set computers (CISCs), different instructions take different amounts of time, so the value measured depends on the instruction mix; even for comparing processors in the same family the IPS measurement can be problematic.
In an example from 2011, typical PC processors like the Intel Core 2 and the AMD Athlon 64 X2 run with a clock of several GHz, which means that one clock cycle is less than 1 nanosecond (typically about 0.3 ns to 0.5 ns on modern desktop CPUs), while main memory has a latency of about 15–30 ns.
A phase-locked loop in the CPU then multiplies the FSB clock by a factor in order to get the CPU speed. [1] Example: A Core 2 Duo E6600 processor is listed as 2.4 GHz with a 1066 MHz FSB. The FSB is known to be quad-pumped, so its clock frequency is 1066/4 = 266 MHz. Therefore, the CPU multiplier is 2400/266, or 9×.
The CPU's clock speed and VCore are automatically decreased when the computer is under low load or idle, to save battery power, reduce heat and noise. The lifetime of the CPU is also extended because of reduced electromigration, which varies exponentially with temperature. [1] The technology is a concept similar to Intel's SpeedStep technology.