Scan Algorithm (Elevator Algorithm)
The Scan Algorithm, often referred to as the Elevator Algorithm, is a disk scheduling approach in which the disk arm moves in a particular direction, satisfying all the requests encountered along its path, before reversing its direction. This method is akin to the operation of an elevator, which moves to the last floor in one direction, and then reverses its path.
C-Scan Algorithm
The C-Scan (Circular Scan) algorithm is an enhancement of the Scan scheduling algorithm. It follows a specific pattern in which the disk arm moves in one direction, servicing requests until it reaches the last cylinder. Then, it jumps to the last cylinder in the opposite direction without servicing any requests. Finally, it reverses direction and begins servicing the remaining requests.
Advantages of C-Scan (Circular Scan)
- Improved Version of SCAN: C-Scan is an improved and more efficient version of the SCAN scheduling algorithm.
- Optimized Movement: The disk arm efficiently moves from one end of the disk to the other, serving all the requests in between.
- Reduced Waiting Time: C-Scan minimizes waiting time for cylinders recently visited by the disk arm, improving overall efficiency.
- Uniform Waiting Time: This algorithm ensures a more uniform waiting time for requests, leading to predictable performance.
- Better Response Time: C-Scan offers better response times for I/O requests, enhancing the user experience.
Disadvantages C-Scan (Circular Scan)
- Increased Seek Movements: C-Scan may result in more seek movements compared to the basic SCAN algorithm, which could lead to increased wear and tear on the disk.
- Unnecessary Travel: Even when no more requests need to be serviced, the disk arm continues to travel to the end of the disk in C-Scan, which can be inefficient compared to the SCAN algorithm.
In summary, the Scan and C-Scan algorithms are disk scheduling methods that aim to efficiently service I/O requests. While C-Scan is an improved version of Scan with advantages such as reduced waiting time and better response times, it may involve more seek movements and unnecessary travel of the disk arm.