Question

What is context switch ? Describe the actions taken by a kernel to context switch between processes

Answer 1

A context switch is a mechanism used by the operating system to change from one process to another to maximize CPU utilization. It involves saving the state of the current process, selecting another process to run, restoring the next process's state, and transferring control to it. Efficient context switching is crucial for system performance in a multitasking environment.

Step-by-step explanation:

A context switch is the process that occurs within a computer's operating system whereby it switches the CPU's focus from one process or thread to another. This is necessary for a multitasking operating system, where it needs to balance multiple processes' usage of the CPU to achieve efficient execution. A context switch can occur for several reasons, such as when a running process needs to wait for a resource, gets interrupted by the system for higher-priority tasks, or when time allocated for its execution elapses (time-slicing).

To perform a context switch, the kernel must carry out several actions to ensure that the system's state is correctly changed from the current process to the next. The following are the main steps taken:

1. The system's state for the currently executing process is saved into its Process Control Block (PCB). This includes the process's current register values, program counter, and other architecture-specific data.
2. The kernel's scheduler selects another process to execute, based on its scheduling algorithm and process priority.
3. The system state for the next process is restored from its PCB. This means the CPU's registers are loaded with the values that were saved when this process was last preempted.
4. The program counter is set to the address of the next instruction to execute for this process, effectively transferring control and allowing the process to continue its execution.

These actions taken by the kernel are essential for the smooth operation of the system, as they allow multiple processes to share the CPU as if each were the only process running. The ability to perform efficient context switches is critical for the perceived performance of the system, especially as the number of processes increases.

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