What is a context switch and when does it occur?

A context switch refers to the process of saving and restoring the state of a process or thread in a computer system. It occurs when the operating system interrupts the execution of a currently running process and switches to another process that is ready to run.

There are several scenarios in which a context switch may occur:

1. Preemptive multitasking: In a preemptive multitasking system, the operating system can interrupt a running process to allocate CPU time to another process. This interruption triggers a context switch, where the state of the currently running process is saved, and the state of the new process is restored.

2. Interrupt handling: When an interrupt occurs, such as a hardware interrupt or a software interrupt, the operating system suspends the execution of the current process and switches to the interrupt handler routine. This involves saving the state of the interrupted process and restoring the state of the interrupt handler.

3. Process scheduling: The operating system may decide to switch to a different process based on its scheduling algorithm. This can happen when a higher-priority process becomes ready to run, or when a time slice allocated to a process expires. In such cases, the current process's state is saved, and the state of the newly selected process is restored.

During a context switch, the operating system saves the current process's state, which typically includes the program counter, registers, and other relevant information. It then restores the saved state of the new process, allowing it to resume execution from where it left off. Context switches are essential for efficient multitasking and resource allocation in an operating system.