Which statement is correct regarding CPU operation and instruction execution?

Question

Which statement is correct regarding CPU operation and instruction execution?

1. A. The Program counter stores the address of the current instruction, executed by the CPU.
2. B. An interrupt is processed only after the completion of the entire program.
3. C. The instruction register stores the current instruction being decoded or executed. (Correct answer)
4. D. All machine instructions require the same number of clock cycles to execute.

Correct Answer

Option C — C

Detailed Solution & Explanation

The correct answer is Option C.

Key Points

• the instruction register stores the current instruction being decoded or executed.
• (Note: the provisional key showed B; the final JKSSB key is C.)
• The Instruction Register (IR) holds the instruction currently being decoded and executed by the control unit — that statement is correct.

Additional Information

• (A) The Program Counter (PC) stores the address of the NEXT instruction to be fetched, not the current one — so this statement is subtly wrong.
• (B) An interrupt is serviced almost immediately (after the current instruction finishes), not only after the entire program completes — that is the whole point of interrupts.
• (D) Different machine instructions take different numbers of clock cycles; they are not all equal.

Exam Tip

• keep the two registers straight — PC = address of next instruction, IR = the instruction itself, right now.