A computer comprising: a security management computing unit configured to manage an auxiliary storage device unit and an I/O device connected thereto; and a user computing unit configured to communicate with the I/O device via an intercommunication unit for enabling communication between the security management computing unit and the user computing unit, wherein the user computing unit has a separate central processing unit CPU and a separate memory which are isolated from the security management computing unit and the user computing unit is connected to the security management computing unit only via the intercommunication unit, wherein the security management computing unit performs I/O device management, system monitoring and restoration, and a monitoring and control of the user computing unit, wherein the user computing unit executes a user program and an OS while isolated from the security management computing unit, wherein the auxiliary storage device unit includes a security management computing storage area and a user computing storage area, the security management computing storage area directly connected to the security management computing unit only and unexposed to the user computing unit, the user computing storage area used by the user computing unit, and an original version of a user OS executed on the user computing unit is stored in the user computing storage area and a duplicated version of the user OS is stored in the security management computing storage area, and wherein the security management computing unit selectively provides the duplicated version of the user OS stored in the security management computing storage area during a booting of the user computing unit. a security management computing unit configured to manage an auxiliary storage device unit and an I/O device connected thereto; and a user computing unit configured to communicate with the I/O device via an intercommunication unit for enabling communication between the security management computing unit and the user computing unit, wherein the user computing unit has a separate central processing unit CPU and a separate memory which are isolated from the security management computing unit and the user computing unit is connected to the security management computing unit only via the intercommunication unit, wherein the security management computing unit performs I/O device management, system monitoring and restoration, and a monitoring and control of the user computing unit, wherein the user computing unit executes a user program and an OS while isolated from the security management computing unit, wherein the auxiliary storage device unit includes a security management computing storage area and a user computing storage area, the security management computing storage area directly connected to the security management computing unit only and unexposed to the user computing unit, the user computing storage area used by the user computing unit, and an original version of a user OS executed on the user computing unit is stored in the user computing storage area and a duplicated version of the user OS is stored in the security management computing storage area, and wherein the security management computing unit selectively provides the duplicated version of the user OS stored in the security management computing storage area during a booting of the user computing unit.