Computer systems in which at least two operating systems coexist independently from each other, and that swap between the operating systems. Provides methods to have at least two operating systems coexist independently of each other and swap the operating systems. A computer system includes a memory allocation component to be called by a power-on self test (POST) routine in order to allocate RAM for the operating systems when the computer system starts up, and backup and restore component to be called by a suspension routine in order to backup and restore the data specific to the operating systems, wherein each of the operating systems can transfer itself to the memory area belonging to itself, turn an allocated memory area into a physical RAM, and call the suspension routine to swap to other operating systems by setting swap parameters. The computer system can swap between operating systems easily and conveniently.