Fetch Decode Execute

• What happens in the Fetch stage?

  An instruction is fetched from the user and stored into memory.
• What happens in the Decode stage?

  Opcode is interpreted to determine what operation must be performed.
• What happens in the Execute stage?

  The execute operation is performed and results are stored in memory.
• What is the first register used in the FDE cycle?

  The Program Counter (PC)
• What is the second register used in the FDE cycle?

  The Memory Address Register (MAR)
• What is the third register used in the FDE cycle?

  The Memory Data Register (MDR)
• What is the fourth register used in the FDE cycle?

  The Current Instruction Register (CIR)