Which CPU stage actually performs the operation specified by an instruction?

Which CPU stage actually performs the operation specified by an instruction?

• A. Fetch
• B. Decode
• C. Execute
• D. Store

Answer: (C)

The action specified by an instruction is carried out in the Execute stage. After fetch brings the instruction into the processor and decode interprets the opcode and operands to set up the operation, the Execute stage uses the ALU or other units to perform the actual arithmetic, logic, or address calculation dictated by the instruction. For example, an ADD instruction causes the ALU to compute the sum of two registers. If the instruction involves memory, the necessary calculation or operation happens here as well, such as computing an effective address. Once the operation is done, the result moves to the Store stage to be written to a register or memory location.

The action specified by an instruction is carried out in the Execute stage. After fetch brings the instruction into the processor and decode interprets the opcode and operands to set up the operation, the Execute stage uses the ALU or other units to perform the actual arithmetic, logic, or address calculation dictated by the instruction. For example, an ADD instruction causes the ALU to compute the sum of two registers. If the instruction involves memory, the necessary calculation or operation happens here as well, such as computing an effective address. Once the operation is done, the result moves to the Store stage to be written to a register or memory location.