The CPU continually reads instructions stored in main memory and executes…

The idea

This statement describes the core behaviour of the CPU: it repeatedly fetches instructions held in main memory and carries them out. Main memory (RAM) stores both the program's instructions and the data being worked on. The CPU does not hold the whole program inside itself; instead it reads one instruction at a time, using the program counter to track the address of the next instruction. Each instruction is fetched, decoded by the control unit, and executed, then the cycle repeats. This is why the Fetch-Execute cycle is described as continuous. A correct multiple-choice answer should recognise that instructions come from main memory and are processed one at a time in a repeating cycle, rather than being stored permanently in the CPU or executed all at once.

What earns the marks

• Instructions are stored in main memory (RAM) and read by the CPU.
• The CPU processes instructions one at a time in a repeating cycle.
• The program counter holds the address of the next instruction to be fetched.
• The control unit decodes each instruction before it is executed.

Common mistakes and how to put them right

• Thinking the CPU permanently stores the program.

  Put it right: Instructions are held in main memory and fetched as needed.

• Believing all instructions execute simultaneously.

  Put it right: They are processed one at a time in sequence.

• Ignoring the role of the program counter.

  Put it right: It tracks the address of the next instruction.

Exam tips

• Read each option carefully and eliminate those that contradict the idea of a repeating cycle.
• Check whether an option confuses storage location (main memory) with the processor.
• Link your reasoning to the Fetch-Execute stages to justify the chosen option.