5.1.6 LOOK Disk Scheduling Algorithm in operating system with example and graphics understanding

Disk Scheduling in Operating System

We are considering external drive here as a disk like CD, DVD, USB Hard disk, USB Pen drive.

Components used in disk
Sectors, track, spindle for rotation, platters, arm, arm assembly, read write head etc.

Structure of Disk
if we look about structure of disk then platters moving around spindle or rotating with respect to spindle. arms are located upside and downside of every platters. Heads are located on every arms for reading and writing purpose. This type of arrangement allowing to read and write from both side of platter. Tracks are divided on platter and there is a further division lead to sectors on every tracks.

Why Disk Scheduling
In this arrangement when head moves on platter for reading data from disk and writing data on disk, it that moment it will consume some amount of time for performing this activity.
According to goals of operating system we want to reduce access time for data, it means we requires fastest execution, as well as parallel we are expanding our memory also.
So to reduce amount of time for reading and writing activity from disk there is need to establish few policies for it and these policies are known as disk scheduling techniques or methods.
There are various techniques for disk scheduling like,
FCFS First come first serve Scheduling
SSTF Shortest seek time first Scheduling
SCAN Scheduling
C-SCAN Scheduling
LOOK Scheduling
C-LOOK Scheduling
1 What is Disk Scheduling

2 FCFS First Come First Serve Scheduling

3 SSTF Shortest Seek Time First Scheduling

4 SCAN Scheduling

5 C-SCAN Scheduling

6 LOOK Scheduling

7 C-LOOK Scheduling