The present invention provides a method of improving the speed of processing of a system and optimizing system performance in RTOS by searching for a task on which occupancy time is the longest in a system mode and transferring a stack from an armored memory to an embedded memory, and by reallocating the stack pointers. According to the present invention, since a microprocessor which has an expensive and large embedded memory does not have to be mounted, costs of manufacturing in mass production can be lowered.