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虽然我们不必了解CPU是如何控制计算机的,正像我们可以驾驶汽车而不必知道内燃机是如何使汽车开动的一样,但是熟悉一些基本概念和基本技术有助于我们理解高性能CPU为什么能如此高速地运行。 一、流水线传送 这种技术能让CPU模仿工厂里流水线的方式工作,把一条指令分成若干部分,分别由不同的部件来执行。典型的流水线将每一条机器指令分成5步,即取指、译码、取操作数(或译码2)、执行、回写。虽然每条指令仍需要占用5个或更多个时钟周期,但是在理想条件,流水线已经平稳的环境下,平均每个时钟周期可以完成一条指令。 另外,还有一种超级流水线的设计,它将机器指令划分为更多级的操作以减轻每一级的复杂程度。其理论基础是:在流水线的每一步中需要执
Although we do not have to know how the CPU controls the computer, just as we can drive a car without having to know how the internal combustion engine is driving the car, familiarity with some basic concepts and basic techniques helps us to understand why high-performance CPUs are so fast run. First, the pipeline transmission This technology allows the CPU to imitate the way the factory pipeline, an instruction is divided into several parts, respectively, by the implementation of different components. The typical pipeline divides each machine instruction into five steps, fetch, decode, fetch (or decode), execute, write back. Although each instruction still takes 5 or more clock cycles, under ideal conditions, the pipeline has been stable environment, an average of one instruction per clock cycle can be completed. In addition, there is a super-pipelined design that divides machine instructions into more levels of operation to reduce the complexity of each level. The theoretical basis is: need to be implemented in every step of the pipeline