The fetched instruction is loaded into the instruction register. The instruction contains bits that specify the action to be performed by the processor. The processor interpretes the instruction and performs the required action. In general, the actions fall into four categories:

• Processor-memory: Data may be transfrred from processor to memory or from memory to processor.
                              
• Processor-I/O: Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module.
                           
• Data processing: The processor may perform some arithmatic or logic operation on data.
                                    
• Control: An instruction may specify that the sequence of execution be altered.

The main line of activity consists of alternating instruction fetch and instruction execution activities. After an instruction is fetched, it is examined to determine if any indirect addressing is involved. If so, the required operands are fetched using indirect addressing.