Operating System Tutorial

Operating System Tutorial Types of Operating System Evolution of Operating System Functions of Operating System Operating System Properties Operating System Services Components of Operating System Needs of the Operating System

Operating Systems

Linux Operating System Unix Operating System Ubuntu Operating System Chrome Operating Systems Fedora Operating System MAC Operating System MS Windows Operating System Solaris Operating System Cooperative Operating System CorelDRAW Operating System CentOS FreeBSD Operating Systems Batch Operating System MS-DOS Operating System Commercial Mobile Operating Systems


Difference Between Multi-programming and Multitasking Difference between C-LOOK and C-SCAN Difference between Rotational Latency and Disk Assess Time Trap vs Interrupt Difference between C-SCAN and SSTF Difference between SCAN and FCFS Difference between Seek Time and Disk Access Time Difference between SSTF and LOOK Difference between Process and Program in the Operating System Difference between Protection and Security in Operating System

How To

How to implement Monitors using Semaphores How to Install a Different Operating System on a PC


What is Kernel and Types of Kernel What is DOS Operating System What is Thread and Types of Thread What is Process Scheduler and Process Queue What is Context Switching What is CPU Scheduling What is Producer-Consumer Problem What is Semaphore in Operating System Monitors in Operating System What is Deadlock What is Paging and Segmentation What is Demand Paging What is Virtual Memory What is a Long term Scheduler What is Page Replacement in Operating System What is BSR Mode What is Convoy Effect What is Job Sequencing in Operating System Why is it critical for the Scheduler to distinguish between I/O-bound and CPU-bound programs Why is there a Need for an Operating System


Process Management Process State Scheduling Algorithm FCFS (First-come-First-Serve) Scheduling SJF (Shortest Job First) Scheduling Round-Robin CPU Scheduling Priority Based Scheduling HRRN (Highest Response Ratio Next) Scheduling Process Synchronization Lock Variable Mechanism TSL Mechanism Turn Variable Mechanism Interested Variable Mechanism Deadlock Avoidance Strategies for Handling Deadlock Deadlock Prevention Deadlock Detection and Recovery Resource Allocation Graph Banker’s Algorithm in Operating System Fixed Partitioning and Dynamic Partitioning Partitioning Algorithms Disk Scheduling Algorithms FCFS and SSTF Disk Scheduling Algorithm SCAN and C-SCAN Disk Scheduling Algorithm Look and C-Look Disk Scheduling Algorithm File in Operating System File Access Methods in Operating System File Allocation Method Directory Structure in Operating System N-Step-SCAN Disk Scheduling Feedback Queue in Operating System Contiguous Memory Allocation in Operating System Real-time Operating System Starvation in Operating System Thrashing in Operating System 5 Goals of Operating System Advantages of Operating System Advantages of UNIX Operating System Bit Vector in Operating System Booting Process in Operating System Can a Computer Run Without the Operating System Dining Philosophers Problem in Operating System Free Space Management in Operating System Inter Process Communication in Operating System Swapping in Operating System Memory Management in Operating System Multiprogramming Operating System Multitasking Operating Systems Multi-user Operating Systems Non-Contiguous Memory Allocation in Operating System Page Table in Operating System Process Scheduling in Operating System Segmentation in Operating System Simple Structure in Operating System Single-User Operating System Two Phase Locking Protocol Advantages and Disadvantages of Operating System Arithmetic operations in binary number system Assemblers in the operating system Bakery Algorithm in Operating System Benefits of Ubuntu Operating System CPU Scheduling Criteria in Operating System Critical Section in Operating System Device Management in Operating System Linux Scheduler in Operating System Long Term Scheduler in Operating System Mutex in Operating System Operating System Failure Peterson's Solution in Operating System Privileged and Non-Privileged Instructions in Operating System Swapping in Operating System Types of Operating System Zombie and Orphan Process in Operating System 62-bit operating system Advantages and Disadvantages of Batch Operating System Boot Block and Bad Block in Operating System Contiguous and Non - Contiguous Memory Allocation in Operating System Control and Distribution Systems in Operations Management Control Program in Operating System Convergent Technologies in Operating System Convoy Effect in Operating System Copy Operating Systems to SSD Core Components of Operating System Core of UNIX Operating System Correct Value to return to the Operating System Corrupted Operating System Cos is Smart Card Operating System Cosmos Operating Systems Examples Generation of Operating System Hardware Solution in Operating System Process Control Block in Operating System Function of Kernel in Operating System Operating System Layers History of Debian Operating Systems Branches and Architecture of Debian Operating Systems Features and Packages of Debian Operating Systems Installation of Operating System on a New PC Organizational Structure and Development in Debian Operating Systems User Interface in Operating System Types Of Memory in OS Operating System in Nokia Multilevel Paging in OS Memory Mapping Techniques in OS Memory Layout of a Process in Operating System Hardware Protection in Operating System Functions of File Management in Operating System Core of Linux Operating System Cache Replacement Policy in Operating System Cache Line and Cache Size in Operating System What is Memory Mapping? Difference Between Network Operating System And Distributed Operating System What is the difference between a Hard link and a Soft Link? Principles of Preemptive Scheduling Process Scheduling Algorithms What is NOS? What is the Interrupt I/O Process? What is Time Sharing OS What is process termination? What is Time-Sharing Operating System What is Batch File File system manipulation What is Message-passing Technique in OS Logical Clock in Distributed System

What is Context Switching

Context Switching is the switching of CPU from one process to another process. Context switching means storing the process state so that we can reload the process when needed, and the execution of the process can be resumed from the same point later. Context Switching is the characteristic of a multitasking operating system. In context switching, one CPU can be shared among several processes. In other words, context switching is the mechanism that permits a single CPU to handle several threads or processes without the need for extra processors.

In context switching, processes are switched so quickly that the user gets the myth that all processes are running simultaneously.

But in the process of context switching, there are lots of steps that we need to follow. We cannot directly change or switch the process from running state to ready state. It is mandatory to save the context of that process. If we do not save the context of the process, while again executing the process, we need to start its execution from the beginning. In reality, the process continues from that state, where the CPU left the process in its previous execution. So, it is required to save the context of the process before placing some other process in the running state. Context means data of CPU registers and program counter anytime.

Context Switching Triggers

The context switching triggers are:

  1. Interrupts
  2. Multitasking
  3. Kernel/user switch

Interrupts: - We require context switching if there is an interruption of CPU to get data from the disk read.

Multitasking: - If the CPU has to move processes in and out of memory so that it can run more than one operation.

Kernel/user switch: - We use kernel/user switch if we require switching between the user mode to the kernel mode.

Steps Involved in Context Switching

With the help of the below figure, we describe the procedure of context switching between the processes, which are P1 and P2.

We can see in the following figure that initially, the P1 process is in running state, and the P2 process is in the ready state. If there occurs some interruption, then it is required to change the state of the P1 process from running to the ready state. When the context of the process P1 is saved, then change the state of the P2 process from ready to the running state. 

What is Context Switching

 There are various steps which are involved in the context switching:

  1. The process P1 context, which is in the running state, will be stored in PCB (Program Control Block). That is called PCB1.
  2. Next, PCB1 is transferred to the appropriate queue, i.e., the I/O queue, ready queue, and the waiting queue.
  3. Then from the ready queue, we choose the new process which is to be executed i.e., the process P2.
  4. Next, we update the PCB (Program Control Block) of the P2 process called PCB2. It includes switching the process state from one to another (ready, blocked, suspend, or exit). If the CPU previously executed process P2, then we get the location of the last executed process so that we can again proceed with the P2 process execution.
  5. In the same manner, if we again need to execute the process P1, then the same procedure is followed.

Information stored in PCB (Program Control Block) for Context Switching

The information stored in PCB for context switching are:

  1. Program counter
  2. Information related Scheduling
  3. Accounting information
  4. Base and limits registers
  5. Changed state