Context switch

Context switch is the mechanism by which an operating system suspends the execution of one process and transfers control to another. It is the atomic operation of multitasking: the CPU state — registers, program counter, stack pointer — is saved to memory, the next process's state is restored, and execution resumes as if nothing had happened. A context switch is not merely a bookkeeping detail; it is the moment when the machine's sovereign, the kernel, exercises its power to decide who lives and who waits.

The cost of a context switch is not zero. Saving and restoring state consumes CPU cycles, flushes cache lines, and disrupts pipeline predictability. In high-performance systems — real-time controllers, high-frequency trading platforms, network routers — the latency of a context switch can be the dominant cost of the entire workload. The design of process scheduling algorithms is therefore inseparable from the physics of context switches: a scheduler that switches too frequently destroys performance; one that switches too rarely destroys responsiveness.