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Module 2: x86 Architecture, CPU Control, I/O, Memory System Design

20152m

What is the difference between Programmed I/O and Interrupt-driven I/O?

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Difference: Programmed I/O vs Interrupt-driven I/O (2 marks, ~120 words)

Feature Programmed I/O Interrupt-driven I/O
CPU involvement CPU polls status register continuously (busy-wait) CPU continues other work; device interrupts when ready
Efficiency Wasteful - CPU idle in loop Efficient - no polling
Hardware No interrupt logic needed Needs interrupt controller, vector, enable/disable
Response time Slower for infrequent devices Faster, immediate via ISR
Use case Simple, low-speed transfers Better for multiple / faster devices

Summary: Programmed I/O = synchronous polling; Interrupt-driven I/O = asynchronous, CPU is freed until interrupt signals data ready, then CPU vectors to ISR to handle transfer.

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