指令周期，又称机器周期或读取－运行周期（fetch-and-execute cycle）是指CPU要运行指令经过的步骤。

• 取得指令：CPU内有程序计数器（PC），它保存了下个要运行的指令的地址。处理器按PC保存的地址，经主内存取得指令的内容，PC加1，经数据总线将指令存入指令暂存器（IR）。
• 解码指令：将IR内的指令译成机器语言。
• 运行指令
• 保存结果

前两步称为取指周期，后两步为运行周期。

An instruction cycle (sometimes called fetch-decode-execute cycle) is the basic operation cycle of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction requires, and carries out those actions. This cycle is repeated continuously by the central processing unit (CPU), from bootup to when the computer is shut down.