Fetch, Decode, Execute Cycle

• Fetch, Decode, Execute (FDE) cycle

  The process by which a processor retrieves and processes instructions and data from memory
• Fetch

  1. The address of the next instruction to be processed is copied from the Program Counter (PC) to the Memory Address Register (MAR)

  2. The PC is incremented to point to the next instruction that will be needed when the cycle starts again

  3. The instruction stored at the location held by the MAR is copied to the MDR
• Decode

  The Control Unit decodes the instruction and sends control signals to the component within or outside the CPU that needs to act
• Execute

  1. The operation indicated by the instruction is performed by the appropriate component

  2. The Arithmetic Logic Unit (ALU) performs the operation given by the Control Unit

  3. The value stored by the Program Counter or Memory Address Register might be changed