C-SCAN (circular SCAN) in Operating Systems - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does C-SCAN stand for in disk scheduling?

C-SCAN stands for Circular SCAN. It is a disk scheduling algorithm that moves the disk arm in one direction servicing requests, then quickly returns to the start without servicing requests on the return.

intermediate

How does C-SCAN differ from the SCAN disk scheduling algorithm?

Unlike SCAN, which moves the disk arm back and forth servicing requests in both directions, C-SCAN only services requests in one direction and jumps back to the beginning without servicing on the return, providing a more uniform wait time.

intermediate

Why is C-SCAN considered fairer than SCAN for servicing disk requests?

C-SCAN treats the disk as a circular list and services requests in one direction only, so all requests get a more uniform wait time because the arm does not service requests on the return trip, avoiding starvation of requests at the edges.

beginner

Describe the movement of the disk arm in C-SCAN scheduling.

The disk arm moves from the lowest to the highest track servicing requests along the way. After reaching the highest track, it quickly returns to the lowest track without servicing any requests during the return, then repeats the process.

beginner

What is a key advantage of using C-SCAN over FCFS (First-Come, First-Served) in disk scheduling?

C-SCAN reduces the average waiting time and provides more predictable service by moving the disk arm in a single direction and avoiding long delays caused by random request order in FCFS.

In C-SCAN, what happens when the disk arm reaches the highest track?

A It reverses direction and services requests on the way back.

B It services requests randomly.

C It stops until new requests arrive.

D It quickly returns to the lowest track without servicing requests.

In C-SCAN, the disk arm moves in one direction and, upon reaching the highest track, jumps back to the lowest track without servicing requests during the return.

Which of the following is a benefit of C-SCAN over SCAN?

A It ignores requests at the edges.

B It services requests in both directions.

C It provides a more uniform wait time for requests.

D It always services the closest request first.

C-SCAN provides a more uniform wait time by servicing requests in one direction only and jumping back without servicing on the return.

What type of scheduling algorithm is C-SCAN?

A CPU scheduling algorithm

B Disk scheduling algorithm

C Memory management algorithm

D Network scheduling algorithm

C-SCAN is a disk scheduling algorithm used to decide the order of servicing disk I/O requests.

How does C-SCAN treat the disk tracks conceptually?

A As a circular list where the arm moves in one direction only.

B As a stack with last-in, first-out order.

C As random points with no order.

D As a linear list with back and forth movement.

C-SCAN treats disk tracks as a circular list, moving the arm in one direction and jumping back to the start.

Which problem does C-SCAN help to reduce compared to FCFS scheduling?

A Long average waiting time due to random request order

B Disk arm starvation

C CPU overload

D Memory fragmentation

C-SCAN reduces long average waiting times caused by random request order in FCFS by servicing requests in a structured, circular manner.

Explain how the C-SCAN disk scheduling algorithm works and why it is used.

Think about how the disk arm moves and how requests are handled in one direction only.

Compare C-SCAN with SCAN disk scheduling in terms of disk arm movement and fairness.

Focus on the direction of movement and how requests are serviced.