What Is a Clocks Per Instruction Value?


Quick Answer

A clocks per instruction value is a computer science term for the number of time periods a computer uses per total instruction count. Clocks per instruction is a measure of computer performance. A lower value is better because it indicates the computer is very fast and efficient.

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Full Answer

A computer contains a central processing unit, or CPU. CPUs complete instructions according to a discrete number of time periods, indicated by an internal time keeper. One electronic pulse of the CPU's time keeper is equivalent to one time period, cycle or clock. Think of it as a single tick of a conventional wall clock, although the CPU's time keeper runs much faster. During a clock, a CPU can complete one simple instruction, such as adding two numbers together.

Most computer operations require several simple instructions, thus requiring multiple clocks. Instructions come in several categories. Every type of complex instruction has a given number of clocks, no more and no less. If four simple instructions comprise a complex instruction, it receives four clocks. The CPU knows how many clocks a complex instruction requires because it has an internal table listing these values.

Find clocks per instruction by multiplying together the number of instructions of a certain type by the number of clocks they require, then dividing that number by the total number of complex instructions. If this involves many types of complex instructions, multiply each type by its required number of clocks, then add to the products of the other types.

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