Accordning to Reference.com, fetch, decode and execute is the basic operation or instruction cycle of a computer's central processing unit in retrieving instructions from programs through the random access module and hard drive. This process is continuously repeated while a computer is in operation.
Fetch is the first step in a sequence of actions performed by the CPU to determine where a request to execute a program or action originated. It relays a series of binary codes to the hard drive and the RAM to process the fetch code for execution. The fetch code also tells the CPU where a program is stored in the hard drive and transfers the instructions to the RAM for execution.
The next sequence is called the decoding action, in which the CPU identifies which computer components are required and assigns them to execute a requested function. This sequence also identifies and provides the required parameters to execute a request successfully.
The execution sequence is the phase in which the CPU directs components how to complete tasks and continuously communicates with them until instructions gathered from the fetch and decode phases are successfully executed.
To speed up operation, modern CPU architecture incorporates an instruction pipeline designed for multiple instruction-cycle executions at the same time.