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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 computer architecture, cycles per instruction (aka clock cycles per instruction, clocks per instruction, or CPI) is one aspect of a processor's performance: the average number of clock cycles per instruction for a program or program fragment. [1] It is the multiplicative inverse of instructions per cycle.
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.
The number of instructions per second is an approximate indicator of the likely performance of the processor. The number of instructions executed per clock is not a constant for a given processor; it depends on how the particular software being run interacts with the processor, and indeed the entire machine, particularly the memory hierarchy.
In simpler CPUs, the instruction cycle is executed sequentially, each instruction being processed before the next one is started. In most modern CPUs, the instruction cycles are instead executed concurrently, and often in parallel, through an instruction pipeline: the next instruction starts being processed before the previous instruction has finished, which is possible because the cycle is ...
In early processors, the TSC was a cycle counter, incrementing by 1 for each clock cycle (which could cause its rate to vary on processors that could change clock speed at runtime) – in later processors, it increments at a fixed rate that doesn't necessarily match the CPU clock speed.
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 ...
Processor clock speeds increased by more than tenfold between 1990 and 1999, and 64-bit processors began to emerge later in the decade. In the 1990s, microprocessors no longer used the same clock speed for the processor and the RAM. Processors began to have a front-side bus (FSB) clock speed used in communication with RAM and other components ...