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Each time the CPU executes an instruction, it takes a series of steps. The complete series of steps is called a machine cycle. A machine cycle can be divided into two smaller cycles. These are instruction cycle and execution cycle. Instruction cycle: In instruction cycle CPU takes two steps-- 1. Fetching: Before the CPU can execute an instruction, the control unit must retrieve or fetch a command or data from the computer\'s memory. 2. Decoding: Before a command can be executed, the control unit must decode the command into instruction set. Execution cycle: In execution cycle CPU also takes two steps-- 1. Executing: When the command is executed, the CPU carried out the instructions in order by converting them into macrocode. 2. Storing: The CPU may be required to store the result of an instruction in memory.