Why disk scheduling reduces seek time in Operating Systems - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does disk scheduling reduce seek time?

Disk scheduling algorithms aim to reduce the seek time of the disk head. Which of the following best explains how they achieve this?

A By rearranging the order of pending disk requests to minimize the movement of the disk head.

B By increasing the speed of the disk head motor to move faster between requests.

C By reducing the number of disk requests generated by the system.

D By storing all data in memory to avoid disk access altogether.

💡 Hint

Think about how changing the order of requests affects the distance the disk head travels.

Disk scheduling algorithms reorder the sequence of disk access requests to reduce the total distance the disk head must move. This minimizes seek time, which is the time taken to position the head over the correct track.

📋 Factual

intermediate

Which disk scheduling algorithm is designed to reduce seek time by servicing requests in one direction before reversing?

Among the common disk scheduling algorithms, which one services requests in one direction until the end, then reverses direction, helping reduce seek time?

A Shortest Seek Time First (SSTF)

B SCAN (Elevator Algorithm)

C First-Come, First-Served (FCFS)

D Random Scheduling

💡 Hint

Think of an elevator moving up and down, servicing requests along the way.

The SCAN algorithm moves the disk head in one direction servicing all requests until it reaches the end, then reverses direction. This reduces seek time by minimizing back-and-forth movement.

🔍 Analysis

advanced

Analyzing seek time reduction with SSTF algorithm

Given the disk requests at tracks 10, 22, 20, 2, 40, and the disk head currently at track 15, which request will the Shortest Seek Time First (SSTF) algorithm service next to reduce seek time?

A Track 10

B Track 2

C Track 22

D Track 20

💡 Hint

Calculate the distance from the current head position to each request and pick the smallest.

SSTF selects the request closest to the current head position. From track 15, distances are: 10 (5), 22 (7), 20 (5), 2 (13), 40 (25). Both 10 and 20 are 5 tracks away, but SSTF typically picks the closest request found first, here track 10.

❓ Comparison

advanced

Comparing FCFS and SCAN in terms of seek time

Which statement correctly compares the seek time behavior of First-Come, First-Served (FCFS) and SCAN disk scheduling algorithms?

A Both FCFS and SCAN have the same seek time because they process all requests eventually.

B FCFS always results in lower seek time than SCAN because it processes requests in arrival order.

C SCAN increases seek time because it moves the disk head back and forth unnecessarily.

D SCAN generally reduces seek time compared to FCFS by servicing requests in a sorted order along the disk tracks.

💡 Hint

Consider how the order of servicing requests affects the total distance the disk head travels.

SCAN reduces seek time by moving the disk head in one direction and servicing requests in order, minimizing back-and-forth movement. FCFS can cause more random movement, increasing seek time.

❓ Reasoning

expert

Why does reducing seek time improve overall system performance?

Reducing seek time is a goal of disk scheduling. Why does this reduction improve overall system performance?

A Because it reduces the power consumption of the disk drive significantly.

B Because it increases the disk storage capacity by optimizing data placement.

C Because it decreases the time the CPU waits for data, allowing faster processing of tasks.

D Because it eliminates the need for caching data in memory.

💡 Hint

Think about how disk access speed affects the CPU's ability to continue working.

Reducing seek time means the disk can deliver data faster. This reduces the time the CPU waits for data, improving the speed of running programs and overall system responsiveness.