A Machine cycle, also known as instruction cycle or a processor cycle. In computer architecture, it is also sometimes called as (fetch-decode-execute cycle). The Machine cycle consist of a sequence of three steps, which includes fetch, decode and execute. But actually there are four steps in the Machine cycle, the fourth one is Store.
In the fetch process, the control unit of the microprocessor retrieve the instruction from the main memory (RAM), that is stored at the address indicated by the Program counter.
The Control unit in the CPU decodes the instruction in the Instruction register. Decoding the instruction in the IR involves the splitting the operand field into its components depending upon the Opcode.
After the Instruction and data is fetched and decoded the instruction is executed by the ALU (arithmetic logical unit) of the CPU. The output of the instruction is generated at this stage. This whole process of generating the output is known as execution (execution cycle).
After the Output is generated the computer stores the results in the memory for later use.
As soon as the instruction is executed and results are saved, machine cycle is restarted and begins with fetch cycle again.