I/O scheduling and buffering in Operating Systems - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding I/O Scheduling Algorithms

Which I/O scheduling algorithm is designed to reduce the average seek time by servicing requests in the order of their position on the disk, moving the disk arm in one direction only until it reaches the end?

A First-Come, First-Served (FCFS)

B SCAN (Elevator Algorithm)

C Shortest Seek Time First (SSTF)

D Circular SCAN (C-SCAN)

💡 Hint

Think of an elevator moving up and down, servicing requests in one direction before reversing.

The SCAN algorithm moves the disk arm in one direction, servicing all requests until it reaches the end, then reverses direction. This reduces seek time compared to FCFS by avoiding unnecessary back-and-forth movement, though SSTF may have lower average seek time but can cause starvation.

📋 Factual

intermediate

Buffering Purpose in I/O Operations

What is the primary purpose of buffering in I/O operations?

A To increase CPU speed during processing

B To permanently save data on disk

C To temporarily store data to handle speed differences between devices

D To encrypt data before transmission

💡 Hint

Consider why data might need a temporary holding place when moving between fast and slow devices.

Buffering temporarily holds data to accommodate differences in speed between the CPU and I/O devices, preventing data loss or CPU waiting.

🔍 Analysis

advanced

Analyzing Effects of Buffering Strategies

Consider a system using double buffering for I/O. What is the main advantage of double buffering compared to single buffering?

A It allows simultaneous reading and writing, reducing idle time

B It halves the memory usage for buffers

C It eliminates the need for I/O scheduling

D It increases the CPU clock speed

💡 Hint

Think about how two buffers can be used to overlap operations.

Double buffering uses two buffers so one can be filled while the other is being emptied, allowing reading and writing to happen at the same time and reducing waiting.

❓ Comparison

advanced

Comparing I/O Scheduling Algorithms

Which of the following statements correctly compares SSTF and C-SCAN scheduling algorithms?

A SSTF always provides fair access to all requests, while C-SCAN can starve some requests.

B Both SSTF and C-SCAN ignore the physical location of requests on the disk.

C SSTF moves the disk arm in a fixed direction, while C-SCAN selects the closest request next.

D C-SCAN moves the disk arm in one direction only, providing more uniform wait times than SSTF.

💡 Hint

Consider how each algorithm moves the disk arm and how that affects wait times.

SSTF selects the closest request next, which can cause starvation for far requests. C-SCAN moves the arm in one direction only, servicing requests in order and then jumping back, providing more uniform wait times.

❓ Reasoning

expert

Impact of Buffer Size on System Performance

A system uses buffering for I/O operations. If the buffer size is increased significantly, which of the following is the most likely effect?

A I/O throughput improves up to a point, but excessive buffer size may increase latency.

B The system will always perform better with larger buffers, with no downsides.

C CPU utilization decreases because larger buffers slow down processing.

D Increasing buffer size causes immediate data loss due to overflow.

💡 Hint

Think about the trade-off between throughput and delay when changing buffer size.

Larger buffers can hold more data, improving throughput by reducing I/O wait times. However, very large buffers can cause delays before data is processed, increasing latency.