Source : Free On-Line Dictionary of Computing

fetch-execute cycle
     
         The sequence of actions that a
        {central processing unit} performs to execute each {machine
        code} instruction in a program.
     
        At the beginning of each cycle the CPU presents the value of
        the {program counter} on the {address bus}.  The CPU then
        fetches the instruction from {main memory} (possibly via a
        {cache} and/or a {pipeline}) via the {data bus} into the
        {instruction register}.
     
        From the instruction register, the data forming the
        instruction is decoded and passed to the {control unit} which
        sends a sequence of control signals to the relevant {function
        units} of the CPU to perform the actions required by the
        instruction such as reading values from {registers}, passing
        them to the {ALU} to add them together and writing the result
        back to a register.
     
        The program counter is then incremented to address the next
        instruction and the cycle is repeated.
     
        The fetch-execute cycle was first proposed by {John von
        Neumann}.
     
        (1998-06-25)