When the CPU switches to another process, the system must save the state of the old process and load the saved state for the new process. This is known as a context switch. When a context switch occurs, the kernel saves the context of the old process in its PCB $($Process Control Board$)$ and loads the saved context of the new process scheduled to run. The more complex the OS and PCB$,$ the longer the context switch.

Interrupts cause the operating system to change a CPU core from its current task and to run a kernel routine. Such operations happen frequently on general$-$purpose systems. When an interrupt occurs, the system needs to save the current context of the process running on the CPU core so that it can restore that context when its processing is done, essentially suspending the process and then resuming it$.$ The context is represented in the PCB of the process.It includes the value of the CPU registers, the process state and memory$-$management information. Generally, we perform a state save of the current state of the CPU core, be it in kernel or user mode, and then a state restore to resume operations.