Which sequence describes the common CPU instruction cycle stages?

Which sequence describes the common CPU instruction cycle stages?

• A. Encode the instruction, then fetch it.
• B. Fetch, Decode, Execute, Access memory if needed, and Write back.
• C. Fetch, Jump, Return.
• D. Decode, Fetch, Execute, Write back.

Answer: (B)

The main idea here is the typical instruction cycle that a CPU goes through to run a instruction: fetch, decode, execute, access memory if needed, and write back. First, fetch reads the next instruction from memory using the program counter, then the PC is advanced to point to the following instruction. Decode interprets the instruction’s opcode to figure out what operation is required and which operands are involved. Execute carries out that operation, with the arithmetic or logic unit performing the computation or action. If the instruction needs data from memory (like a load or a store), the next step handles that access. Finally, write-back places the result into the appropriate destination, such as a register or memory location. Other sequences don’t fit the standard flow: encoding isn’t part of the runtime cycle, and actions like jump or return are specific control-flow operations rather than the generic cycle; and decoding before fetching would leave no instruction to decode.