Advantages and Disadvantages of various Disk scheduling algorithms
Prerequisite – Disk Scheduling Algorithms
1. First Come First Serve (FCFS) :
Advantages –
- First Come First Serve algorithm has a very simple logic, it executes the process requests one by one in the sequence they arrive.
- Thus, First Come First Serve is very simple and easy to understand and implement.
- In FCFS eventually, each and every process gets a chance to execute, so no starvation occur.
Disadvantages –
- This scheduling algorithm is nonpreemptive, which means the process can’t be stopped in middle of execution and will run it’s full course.
- FCFS being a nonpreemptive scheduling algorithm, the short processes which are at the back of the queue have to wait for the long process at the front to finish
- The throughput of FCFS is not very efficient.
- FCFS is implemented on small systems only where input-output efficiency is not of utmost importance.
2. Shortest Seek Time First (SSTF) :
Advantages –
- The total seek time is reduced compared to First Come First Serve.
- SSTF improves and increases throughput.
- Less average waiting time and response time in SSTF.
Disadvantages –
- In SSTF there is an overhead of finding out the closest request.
- Starvation may occur for requests far from head.
- In SSTF high variance is present in response time and waiting time.
- Frequent switching of the Head’s direction slows the algorithm.
3. SCAN :
Advantages –
- Scan scheduling algorithm is simple and easy to understand and implement.
- Starvation is avoided in SCAN algorithm.
- Low variance Occurs in waiting time and response time.
Disadvantages –
- Long waiting time occurs for the cylinders which are just visited by the head.
- In SCAN the head moves till the end of the disk despite the absence of requests to be serviced.
4. C-SCAN :
Advantages –
- C-SCAN Algorithm is the successor and the improved version of the SCAN scheduling Algorithm.
- The Head move from one end to the other of the disk while serving all the requests in between.
- The waiting time for the cylinders which were just visited by the head is reduced in C-SCAN compared to the SCAN Algorithm.
- Uniform waiting time is provided.
- Better response time is provided.
Disadvantages –
- More seek movements are caused in C-SCAN compared to SCAN Algorithm.
- In C-SCAN even if there are no requests left to be serviced the Head will still travel to the end of the disk unlike SCAN algorithm.
5. LOOK :
Advantages –
- If there are no requests left to be services the Head will not move to the end of the disk unlike SCAN algorithm.
- Better performance is provided compared to SCAN Algorithm.
- Starvation is avoided in LOOK scheduling algorithm.
- Low variance is provided in waiting time and response time.
Disadvantages –
- Overhead of finding the end requests is present.
- Cylinders which are just visited by Head have to wait for long time.
6. C-LOOK :
Advantages –
- In C-LOOK the head does not have to move till the end of the disk if there are no requests to be serviced.
- There is less waiting time for the cylinders which are just visited by the head in C-LOOK.
- C-LOOK provides better performance when compared to LOOK Algorithm.
- Starvation is avoided in C-LOOK.
- Low variance is provided in waiting time and response time.
Disadvantages –
- In C-LOOK an overhead of finding the end requests is present.
Last Updated :
16 Apr, 2020
Like Article
Save Article
Share your thoughts in the comments
Please Login to comment...