In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point, and then restoring a different, previously saved, state.[1] This allows multiple processes to share a single central processing unit (CPU), and is an essential feature of a multitasking operating system.

Some operating systems also require a context switch to move between user mode and kernel mode tasks

For example, in the Linux kernel, context switching involves loading the corresponding process control block (PCB) stored in the PCB table in the kernel stack to retrieve information about the state of the new process. CPU state information including the registers, stack pointer, and program counter as well as memory management information like segmentation tables and page tables (unless the old process shares the memory with the new) are loaded from the PCB for the new process. To avoid incorrect address translation in the case of the previous and current processes using different memory, the translation lookaside buffer (TLB) must be flushed. This negatively affects performance because every memory reference to the TLB will be a miss because it is empty after most context switches.[3][4]

Furthermore, analogous context switching happens between user threads, notably green threads, and is often very lightweight, saving and restoring minimal context. In extreme cases, such as switching between goroutines in Go, a context switch is equivalent to a coroutine yield, which is only marginally more expensive than a subroutine call.