MODULE 4 (STORAGE MANAGEMENT)

disk scheduling

• It is usually done by the OS to schedule I/O requests arriving for the disk.

• Goal: to minimize seek time (time taken to reach up to desired track).

FCFS/FIFO

is the easiest disk scheduling algorithm among all the scheduling algorithms.

FCFS/FIFO

each input/output request is served in the order in which the requests arrive.

FCFS/FIFO

In this algorithm, starvation does not occur because ____ address each request.

SSTF (Shortest Seek Time First)

In this type of disk scheduling, the job which has less seek time will be executed first.

SCAN

In this algorithm, we move the disk arm into a specific direction (direction can be moved towards large value or the smallest value).

SCAN

Each request is addressed that comes in its path, and when it comes into the end of the disk, then the disk arm will move reverse, and all the requests are addressed that are arriving in its path.

SCAN

is also called an elevator algorithm because its working like an elevator.

C-SCAN

stands for Circular-SCAN

C-SCAN

is an enhanced version of SCAN disk scheduling.

C-SCAN

the disk head starts to move at one end of the disk and moves towards the other end and service the requests that come in its path and reach another end. After doing this, the direction of the head is reversed. The head reaches the first end without satisfying any request and then it goes back and services the requests which are remaining.

Look

is an enhanced version of SCAN disk scheduling. 

Look

is the same as SCAN disk scheduling, but in this scheduling, instead of going till the last track, we go till the last request and then change the direction.

C-look

means circular-look.

C-look

It takes the advantages of both the disk scheduling C-SCAN, and Look disk scheduling.

C-look

the disk arm moves and service each request till the head reaches its highest request, and after that, the disk arm jumps to the lowest cylinder without servicing any request, and the disk arm moves further and service those requests which are remaining.