Programmed I/O vs interrupt-driven I/O in Operating Systems - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Difference in CPU usage between Programmed I/O and Interrupt-driven I/O

Which statement correctly describes how the CPU is used in Programmed I/O compared to Interrupt-driven I/O?

A In Programmed I/O, the CPU performs other tasks and ignores the device, while in Interrupt-driven I/O, the CPU waits actively for the device.

B Both Programmed I/O and Interrupt-driven I/O require the CPU to wait actively for the device at all times.

C In Programmed I/O, the CPU waits actively for the device, while in Interrupt-driven I/O, the CPU can perform other tasks until interrupted.

D Both Programmed I/O and Interrupt-driven I/O allow the CPU to perform other tasks without waiting.

💡 Hint

Think about whether the CPU is busy checking the device or free to do other work.

Programmed I/O makes the CPU wait and check the device continuously, using CPU time actively. Interrupt-driven I/O lets the CPU do other work and only stops it when the device signals an interrupt.

📋 Factual

intermediate

Main disadvantage of Programmed I/O

What is the main disadvantage of using Programmed I/O compared to Interrupt-driven I/O?

A It requires complex hardware to handle interrupts.

B It causes inefficient CPU usage due to constant polling of the device.

C It cannot handle multiple devices simultaneously.

D It causes data loss because the CPU ignores device signals.

💡 Hint

Consider what happens when the CPU keeps checking the device repeatedly.

Programmed I/O wastes CPU time by constantly checking the device status, even when the device is not ready, leading to inefficiency.

🔍 Analysis

advanced

Impact on system responsiveness

How does Interrupt-driven I/O improve system responsiveness compared to Programmed I/O?

A By allowing the CPU to respond immediately to device signals without wasting time polling.

B By making the CPU poll devices more frequently to detect readiness faster.

C By using a dedicated CPU core solely for I/O operations.

D By disabling all other CPU tasks until the I/O operation completes.

💡 Hint

Think about how the CPU reacts to device readiness in both methods.

Interrupt-driven I/O lets the CPU continue other tasks and only stops it when the device signals readiness, improving responsiveness and efficiency.

❓ Comparison

advanced

Which I/O method is better for high-speed devices?

Considering device speed and CPU efficiency, which I/O method is generally better for high-speed devices and why?

A Interrupt-driven I/O, because it reduces CPU idle time and handles frequent device signals efficiently.

B Programmed I/O, because it allows the CPU to poll the device continuously for immediate data transfer.

C Programmed I/O, because it uses interrupts to notify the CPU only when data is ready.

D Interrupt-driven I/O, because it disables the CPU until the device finishes its operation.

💡 Hint

Think about how frequent device signals affect CPU workload in each method.

High-speed devices generate frequent signals; interrupt-driven I/O handles these efficiently by interrupting the CPU only when needed, avoiding constant polling.

❓ Reasoning

expert

Effect of Programmed I/O on multitasking systems

In a multitasking operating system, what is a likely effect of using Programmed I/O instead of Interrupt-driven I/O?

A Programmed I/O enhances multitasking by prioritizing I/O tasks over CPU tasks automatically.

B Programmed I/O improves multitasking by allowing the CPU to switch tasks only after device polling completes.

C Programmed I/O has no effect on multitasking because I/O operations run independently of CPU scheduling.

D Programmed I/O can cause poor multitasking performance because the CPU spends too much time polling devices, delaying other tasks.

💡 Hint

Consider how CPU time spent polling affects the ability to run multiple tasks smoothly.

Programmed I/O wastes CPU cycles on polling, which reduces the CPU time available for other tasks, hurting multitasking performance.