Definition of polling in I/O handling: Polling means the CPU repeatedly checks device status within the normal instruction flow, not that it pauses execution to run a separate I/O routine automatically.

Introduction / Context:Polling and interrupts are two fundamental I/O servicing methods. Polling is software-driven status checking performed by the CPU at regular intervals or in loops. Interrupts are hardware-driven events that suspend the current instruction stream to service an interrupt handler. This question distinguishes these mechanisms.

Given Data / Assumptions:

• Polling involves reading device status registers to decide when to transfer data.
• Interrupts cause an automatic context switch to a service routine.
• DMA is independent of polling vs. interrupts.

Concept / Approach:In polling, the CPU executes normal code that includes checks like “is transmit buffer empty?” or “has data arrived?” If the condition is met, it performs I/O; otherwise, it continues or waits in a controlled loop. There is no automatic diversion by hardware. In interrupts, hardware signals the CPU to pause the current flow and jump to an ISR, then return after servicing.

Step-by-Step Solution:

Verification / Alternative check:Trace program counters: in polling, execution follows the main path; in interrupts, the PC saves the current location and jumps to the ISR upon an interrupt request.

Why Other Options Are Wrong:

• “Pauses to execute an interrupt routine” describes interrupts, not polling.
• “Correct only with DMA/RTOS/serial” imposes irrelevant constraints; polling is general.

Common Pitfalls:Confusing busy-wait polling with blocking delays; assuming polling cannot meet real-time needs (it can, if loop timing is bounded); overlooking CPU usage overhead of continuous polling vs. interrupt efficiency.

Final Answer:Correct: polling is active status checking in the main program flow