Provided is a manner of switching between the operating environment of a primary OS and the operating environment of a secondary OS. In certain embodiments, a HDD keeps a runtime image of the secondary OS generated in a system memory. A DMA space for allowing the secondary OS to operate is formed in a physical address space where a memory image of the primary OS is active. The runtime image of the secondary OS is transferred to the DMA space. The operation of the memory image of the primary OS is stopped and the runtime image of the secondary OS is executed in the DMA space. Before activating the memory image of the primary OS, the runtime image of the secondary OS is saved to the HDD again.