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GATE CSE 2025 Session 1 Q11: Order of steps when an interrupt arrives

Question

Suppose a program is running on a non-pipelined single processor computer system. The computer is connected to an external device that can interrupt the processor asynchronously. The processor needs to execute the interrupt service routine (ISR) to serve this interrupt. The following steps (not necessarily in order) are taken by the processor when the interrupt arrives:

(i) The processor saves the content of the program counter. (ii) The program counter is loaded with the start address of the ISR. (iii) The processor finishes the present instruction.

Which ONE of the following is the CORRECT sequence of steps?

Try it: multiple choice: exactly one correct option

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Answer: A (official GATE 2025 final answer key)

Concept used: Interrupt handling: interrupts are recognised between instructions, and the return address is saved before jumping to the ISR.

First step: The current instruction must complete first; then the PC (return address) is saved before it is overwritten.

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Source: official GATE 2025 Session 1 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key

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