Instruction Cycle In a digital computer the instructions are stored in the memory. When an instruction is executed it goes through a sequence of operations called an instruction cycle. The total time taken by the computer in executing an instruction is called an instruction cycle. It may contain different subcycle such as machine cycle. An instruction under execution may take one or more machine cycle for its execution depending upon the format of the instruction. Figure shows the steps taken by an instruction during its execution. All these steps together constitute an instruction cycle. Phases of Instruction cycle: 1. Fetch an instruction from memory. 2. Decode the instruction. 3. Read the effective address from memory if the instruction has an indirect address.