What happens during a context switch?

• A. The OS schedules the next task without saving any state.
• B. The OS restarts the current task from the beginning.
• C. The OS saves the current processor state and restores the next task's state.
• D. Only memory contents are swapped; registers are not saved.

Answer: (C)

During a context switch, the OS saves the current processor state and restores the next task's state. This keeps each task's progress and data intact while the CPU moves between tasks. The processor state includes general-purpose registers, the program counter (where execution should resume), the stack pointer, and status flags. In many systems, additional state like floating-point or SIMD registers may also be saved. All of this is stored in the task’s control block, and the scheduler then loads the next task’s saved state so it can resume exactly where it left off. If virtual memory is in use, the OS may also switch the memory mappings (page tables/TLB) as part of the switch. This combination enables true multitasking by swapping in and out complete execution contexts.