How does an operating system perform task switching?

An operating system performs task switching through a process known as context switching, managed by the scheduler.

Context switching is a critical function of a multitasking operating system. It allows the operating system to manage multiple tasks or processes that are running concurrently on a single processor. The operating system can switch between these tasks, giving the illusion that they are running simultaneously, even though only one task is being executed at any given moment.

The process of context switching begins when the operating system's scheduler decides to interrupt the currently running task. This decision could be based on a variety of factors, such as the task's priority level, the amount of time it has been running, or the arrival of a higher-priority task. Once the decision is made, the operating system saves the state of the current task, including the values of its CPU registers and program counter, into a data structure known as a process control block (PCB).

The operating system then loads the PCB of the next task to be executed. This PCB contains all the information needed to resume the task, including the values of its CPU registers and program counter. The operating system loads these values into the CPU, effectively switching the context from the previous task to the new one. The new task then begins executing from the point where it was last interrupted.

This process of saving and loading PCBs allows the operating system to switch between tasks quickly and efficiently. However, it's worth noting that context switching is not without cost. It requires a significant amount of processing power and can lead to performance issues if not managed properly. Therefore, the operating system's scheduler must be designed to minimise the frequency of context switches while still ensuring that all tasks receive their fair share of CPU time.

In summary, task switching in an operating system is achieved through the process of context switching, where the state of a running task is saved and the state of the next task is loaded, allowing the CPU to switch between tasks.