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What is Context Switching?
Context switching is a fundamental concept in multitasking operating systems that allows multiple tasks or processes to share a single processor. In a multitasking environment, the operating system allocates a specific amount of time to each task, allowing them to execute concurrently. However, since there can only be one task running on the CPU at a time, the operating system needs to efficiently switch between these tasks to give an illusion of parallel execution.
Switching in a multitasking environment
In a multitasking environment, such as a modern operating system, several processes or tasks may be running concurrently. These processes can be user applications, system services, or even parts of the operating system itself. Since there is a limited number of CPU cores available, the tasks have to share the CPU’s processing power.
The operating system schedules these tasks based on their priority and assigns a time slice, also known as a quantum or time quantum, to each task. A time slice represents the maximum amount of time a task can utilize the CPU before being preempted and leaving the CPU available for another task. The smaller the time slice, the more frequently tasks will be switched.
When a task’s time slice expires, the operating system performs a context switch. This is the process of saving the task’s current execution state and loading the state of the next task. The execution state of a task includes the values of its registers, program counter, stack pointer, and other relevant information. The operating system stores this information in a data structure called the task control block (TCB).
During a context switch, the operating system performs the following steps:
1. Save the current task’s execution state, including registers and program counter, to its TCB.
2. Select the next task to be executed based on its priority or scheduling algorithm.
3. Load the execution state of the selected task from its TCB into the CPU registers.
4. Resume the execution of the selected task from where it left off.
Context switching involves overhead due to the need to save and restore the execution state of tasks. However, it allows for the efficient utilization of CPU resources and enables the execution of multiple tasks simultaneously despite having a single processor.
Context switching is vital for balancing system responsiveness, ensuring fairness among tasks, and preventing a single task from monopolizing the CPU for an extended period. Understanding context switching is crucial for developers and system administrators to optimize system performance and resource allocation.
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