Which sequence describes how the CPU processes an instruction?

• A. Execute, decode, fetch
• B. Fetch, decode, execute
• C. Decode, fetch, execute
• D. Fetch, execute, decode

Answer: (B)

The CPU handles each instruction in three steps: fetch, then decode, then execute. It starts by fetching the instruction from memory using the program counter, bringing the opcode and operands into the instruction register. Next, it decodes what that instruction means—figuring out which operation to perform and which data or registers are involved. Finally, it executes the instruction, carrying out the operation with the ALU or other CPU components, and then moves the program counter to the next instruction.

This order makes sense because you must know what to do before you do it, and you can only know the operation once you’ve read and interpreted the instruction. Fetching after executing or decoding before fetching would leave the CPU without the necessary data to perform the operation.