→ A context switch (also sometimes referred to as a process switch or a task switch) is the switching of the CPU (central processing unit) from one processor thread to another.
→ Context switches can occur only in kernel mode. Kernel mode is a privileged mode of the CPU in which only the kernel runs and which provides access to all memory locations and all other system resource
→ Other programs, including applications, initially operate in user mode, but they can run portions of the kernel code via system calls
→ The existence of these two modes in Unix-like operating systems means that a similar, but simpler, operation is necessary when a system call causes the CPU to shift to kernel mode. This is referred to as a mode switch rather than a context switch, because it does not change the current process.
→ Context switch between the processes involves mode switch also.