What is context switching and what is its overhead?

Context switching is the process of saving the state of a currently running process and loading the state of another process to execute. The OS saves CPU registers, program counter, and memory mappings to the Process Control Block (PCB). Overhead includes: direct cost (saving/restoring state), indirect cost (cache and TLB invalidation, pipeline flush). Frequent context switches reduce efficiency, so modern schedulers balance responsiveness with overhead minimization.