...

• Thus, the execution of every instruction follows the sequence

  IF

  ID

  EX

  MEM

  WB

  (although not every stage is active in processing every kind of instruction)

• In a straightforward, sequential implementation, some instructions can be completed in less than five steps, by skipping inactive stages

• The PC is written in the MEM stage
• The registers are written in the WB stage
• Backward arrows cause trouble later...