Context Switching in Operating System Last Updated : 07 Apr, 2025 Comments Improve Suggest changes Like Article Like Report Context Switching in an operating system is a critical function that allows the CPU to efficiently manage multiple processes. By saving the state of a currently active process and loading the state of another, the system can handle various tasks simultaneously without losing progress. This switching mechanism ensures optimal use of the CPU, enhancing the system's ability to perform multitasking effectively.Example of Context SwitchingSuppose the operating system has (N) processes stored in a Process Control Block (PCB). Each process runs using the CPU to perform its task. While a process is running, other processes with higher priorities queue up to use the CPU and complete their tasks.Switching the CPU to another process requires saving the state of the current process and restoring the state of a different process. This task is known as a context switch. When a context switch occurs, the kernel saves the context of the old process in its PCB and loads the saved context of the new process scheduled to run. Context-switch time is pure overhead because the system does no useful work while switching. The switching speed varies from machine to machine, depending on factors such as memory speed, the number of registers that need to be copied, and the existence of special instructions (such as a single instruction to load or store all registers). A typical context switch takes a few milliseconds.Context-switch times are highly dependent on hardware support. For example, some processors (such as the Sun UltraSPARC) provide multiple sets of registers. In this case, a context switch simply requires changing the pointer to the current register set. However, if there are more active processes than available register sets, the system resorts to copying register data to and from memory, as before. Additionally, the more complex the operating system, the greater the amount of work that must be done during a context switch.Need of Context SwitchingContext switching enables all processes to share a single CPU to finish their execution and store the status of the system's tasks. The execution of the process begins at the same place where there is a conflict when the process is reloaded into the system.The operating system's need for context switching is explained by the reasons listed below.One process does not directly switch to another within the system. Context switching makes it easier for the operating system to use the CPU's resources to carry out its tasks and store its context while switching between multiple processes.Context switching enables all processes to share a single CPU to finish their execution and store the status of the system's tasks. The execution of the process begins at the same place where there is a conflict when the process is reloaded into the system.Context switching only allows a single CPU to handle multiple processes requests parallelly without the need for any additional processors.Context Switching TriggersThe three different categories of context-switching triggers are as follows.InterruptsMultitaskingUser/Kernel switchInterrupts: When a CPU requests that data be read from a disc, if any interruptions occur, context switching automatically switches to a component of the hardware that can handle the interruptions more quickly.Multitasking: The ability for a process to be switched from the CPU so that another process can run is known as context switching. When a process is switched, the previous state is retained so that the process can continue running at the same spot in the system.Kernel/User Switch: This trigger is used when the OS needed to switch between the user mode and kernel mode.When switching between user mode and kernel/user mode is necessary, operating systems use the kernel/user switch.What is Process Control Block(PCB)? The Process Control block(PCB) is also known as a Task Control Block. it represents a process in the Operating System. A process control block (PCB) is a data structure used by a computer to store all information about a process. It is also called the descriptive process. When a process is created (started or installed), the operating system creates a process manager.Working Process Context Switching State Diagram of Context SwitchingIn the context switching of two processes, the priority-based process occurs in the ready queue of the process control block. Following are the steps:The state of the current process must be saved for rescheduling. The process state contains records, credentials, and operating system-specific information stored on the PCB or switch.The PCB can be stored in a single layer in kernel memory or in a custom OS file.A handle has been added to the PCB to have the system ready to run.The operating system aborts the execution of the current process and selects a process from the waiting list by tuning its PCB.Load the PCB's program counter and continue execution in the selected process.Process/thread values can affect which processes are selected from the queue, this can be important. 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The term was defined by David Patterson, Ga 15 min read PracticeLast Minute Notes – Operating SystemsAn Operating System (OS) is a system software that manages computer hardware, software resources, and provides common services for computer programs. It acts as an interface between the user and the computer hardware.Table of Content Types of Operating System (OS): ThreadsProcessCPU Scheduling Algor 15+ min read Operating System Interview QuestionsAn operating system acts as a GUI between the user and the computer system. In other words, an OS acts as an intermediary between the user and the computer hardware, managing resources such as memory, processing power, and input/output operations. Here some examples of popular operating systems incl 15+ min read Operating Systems - GATE CSE Previous Year QuestionsThe Operating System(OS) subject has high importance in GATE CSE exam because:large number of questions nearly 10-12% of the total asked significant weightage (9-11 marks) across multiple years which can also be seen in the below given table:YearApprox. Marks from OSNumber of QuestionsDifficulty Lev 2 min read Like