What are instruction cycles, machine cycles, and clock cycles?

1、 Instruction cycle ： Is the time to take out an instruction and execute it . Generally, it consists of several machine cycles , Is to get instructions from 、 The total time required to analyze an instruction until it is executed .

The instruction cycle type has the instruction cycle of non access instruction 、 Instruction cycle of fetch instruction 、 Instruction cycle of memory instruction 、 Instruction cycle of null operation instruction and branch instruction .

2、 Machine cycle ： In the computer , For ease of management , The execution of an instruction is often divided into several stages , Complete a task at each stage . for example , Take command 、 Memory read 、 Memory writing, etc , Each of these tasks is called a basic operation .

3、 Clock cycle ： Also known as oscillation period , Defined as the reciprocal of the clock frequency . The clock cycle is the most basic in a computer 、 The smallest unit of time . In a clock cycle ,CPU Just complete one basic action . A clock cycle is an amount of time . The clock cycle represents SDRAM Maximum frequency of operation .

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The reason why computers can work automatically , Because CPU Can take an instruction from the memory of the program and execute it ; Then there is the instruction , Execution instruction , It's all over again , It forms a closed cycle . Unless a shutdown command is encountered , Otherwise the cycle will continue .

The machine cycle consists of several cycles S cycle ( State Period ) form . It is usually specified by the shortest time to read an instruction word in memory CPU cycle ,( That is to say The time required for a computer to complete one or more micro operations through an internal or external bus )), It is generally made up of 12 Clock cycles ( Oscillation period ) form , Also by 6 State cycle composition .

The clock cycle represents SDRAM Maximum frequency of operation . Smaller clock cycles mean higher operating frequencies . about PC100 Specifications of memory , Its operating clock cycle should not be higher than 10 nanosecond . The conversion relationship between nanosecond and operating frequency is :1000 / Clock cycle = Working frequency . for example , Nominal 10 Nanosecond PC100 Memory chip , The expression of its working frequency should be 1000 / 10 = 100MHZ, This indicates that the rated working frequency of this memory chip is 100MHZ.