In synchronousdigitalelectronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. A clock signal oscillates between a high and a low state, normally with a 50% duty cycle. In other words, the signal is a square wave. The circuits using the clock signal for synchronization may become active at either the rising or falling edge, or both (see for example DDR SDRAM), of the clock signal.
Most integrated circuits of sufficient complexity require a clock signal in order to synchronize different parts of the chip and to account for propagation delays. As chips get more complex, the problem of supplying accurate and synchronized clocks to all the circuits becomes more and more difficult. The preeminent example of such complex chips is the microprocessor, the central part of modern computers.
The speed of a clock signal in a computer is called the clock rate or clock frequency.
A clocksignal oscillates between a high and a low state, normally with a 50% duty cycle, and is usually a square wave.
Such sine wave clocks are often differential signals, because this type of signal has twice the slew rate, and therefore half the timing uncertainty, of a single-ended signal with the same voltage range.
The clocksignal is usually distributed across a chip by a recursive H tree.
In computer architecture, Instructions Per Clock (Instruction Per Cycle or IPC) is a term used to describe one aspect of a processor's performance: the average number of individual assembler instructions executed for each clockcycle.
The number of instructions per second for a processor can be derived by multiplying the instructions per clock and the clock speed (measured in cycles per second or Hz) of the processor in question.
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.
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