n. A privileged CPU mode. Sometimes called supervisor mode. Parts of the operating system,
such as the scheduler, device drivers, and the memory manager, usually execute in kernel mode, whereas application code executes in user mode. The transition from user mode to kernel mode is typically made somewhere inside an OS system call when a software interrupt instruction is executed.
Many of the statically linked single–memory space RTOSes used in embedded systems never place the processor into user mode. Thus, the threads running on top of such an RTOS can execute any CPU instruction, even those, such as disable interrupts, that could bring the RTOS to its knees. Note that some processors support multiple levels of privilege, in what are then typically called protection rings.Contrast with user mode.