When the CPU fetches an instruction, what does it retrieve?

When the CPU fetches an instruction, it retrieves the next instruction from main memory. This process is fundamental to how the CPU operates within the fetch-execute cycle, which consists of fetching, decoding, and executing instructions.

During the fetch phase, the CPU uses the program counter to determine the address of the next instruction to be executed. It then retrieves this instruction from main memory and places it into the instruction register. This ensures that the CPU has the necessary instructions to execute the program.

The other options do not accurately reflect what happens during the fetch phase. While data from secondary storage may be involved later in the processing or when data needs to be loaded into main memory, it is not directly related to fetching an instruction. Memory addresses themselves are part of the process but do not constitute the instruction being fetched. The result from the previous calculation may be relevant for subsequent instructions, but it is not what is retrieved during the instruction fetch phase. Thus, the retrieval of the next instruction from main memory is a precise description of what occurs when the CPU fetches an instruction.