Disk Scheduling: As we know that on a single Computer we can Perform Many Operations at a Time so that Management is also necessary on all the Running Processes those are running on the System at a Time. With the help or Advent of the Multi-programming we can Execute Many Programs at a Time. So fir Controlling and providing the Memory to all the Processes Operating System uses the Concept of Disk Scheduling.
In this the Time of CPU is divided into the various Processes and also determines that all the processes will Work Properly. So that Disk Scheduling Will Specifies that at which time which Process will be executed by the CPU. So that the Scheduling means to Execute all the Processes those are given to a CPU at a Time.
The Scheduling is used for Divide the Total Time of the CPU between the Number or Processes So that the Processes can execute Concurrently at a Single Time. For Sharing the Time or For Dividing the Total Time of the CPU, the CPU uses the following the Scheduling Techniques.
1) FCFC or First Come First Serve: In this Jobs or Processes are Executed in the Manner in which they are entered into the Computer. In this Operating System Creates a Queue which contains the Sequence Order in which they are to be Executed and the Sequence in which the CPU will Execute the Process.. In this all the Jobs are performed according to their Sequence Order as they have entered. In this the Job which had Requested first will firstly performed by the CPU. And the Jobs those are entered Later will be Executed in to their Entering Order.
1) SSTF or Shortest Seek Time First :- in this Technique The Operating System will Search for the Shortest time means this will search which job will takes a Less Time of CPU for Running. And After Examining all the jobs, all the Jobs are arranged in the Sequence wise or they are Organized into the Priority Order. The Priority of the Process will be the Total Time which a Process will use For Execution. The Shortest Seek Time Will Include all the Time means Time to Enter and Time to Completion of the Process. Means the Total Time which a Process Will Take For Execution.
4) C-Scan Scheduling: - In the C-Scan all the Processes are Arranged by using Some Circular List. Circular List is that in which there is no start and end point of the list means the End of the List is the Starting Point of the list. In the C-Scan Scheduling the CPU will search for the Process from Start to end and if an End has Found then this again start from the Starting Process. Because Many Times When a CPU is executing the processes then may a user wants to enter some data means a user wants to enter Some data So that at that Situation the CPU will Again Execute that Process after the Input Operation. So that C-Scan Scheduling is used for Processing Same Processes again and Again.
5) Look Scheduling :- In the Look Scheduling the CPU Scans the List from Starting to End of the Disk in which the various Processes are Running and in the Look Scheduling the CPU will Scan the Entire Disk from one End to the Second end.
1) Round Robin. : In the Round Robin Scheduling the Time of CPU is divided into the Equal Numbers which is also called as Quantum Time. Each Process which is Request for Execution will Consumes the Equal Number of Times of the CPU and after the Quantum Time of First Process, the CPU will automatically goes to the Next Process. But the Main Problem is that after the Completion of the Process the Time Will also be Consumed by the Process. Means if a Process either or not have Some Operations To perform the Time of CPU will also be Consume by the CPU , So this is the Wastage of the Time of the CPU.
2) Priority Scheduling : In this Each Process have Some Priorities Assign To them , Means each and Every Process will be Examined by using the Total Time Which will be Consumed by the Process. The Total Time of the Process, and Number of times a Process needs Some Input and Output and Number of Resources will be Examines to set the Priorities of the Processes. So that all the Processes are Arranged into the Form of these Criteria’s and After that they will be Processed by the CPU.
3) Multilevel Queue: The Multilevel Queue is used when there are multiple queues for the various different processes as we know that there are many different types of Works those are to be performed on the Computers at a Time. So that for organizing the various or different Types of Queues the CPU Maintains the Queues by using this Technique. In this all the queues are Collected and Organized in the Form of Some Functions which they are requesting to perform. So that the various Types of Queues are maintained which contains all the Processes which have Same Type.