An auxiliary storage device for a computing unit connected thereto, the auxiliary storage device comprising: a central processing unit, CPU, which is separately equipped from the computing unit and configured to independently protect data stored in the auxiliary storage device independent of the computing unit and to independently monitor access to the data; a memory unit connected to the CPU; a storage medium unit connected to the CPU; an input and output, I/O device connected to the CPU; a mode selection switch which is connected to the I/O device and configured to select any one of a normal mode and a recovery mode by providing a permission signal in hardware; and a communication interface unit configured to provide a connection between the CPU and the computing unit, wherein the storage medium unit comprises a user area in which an operating system, OS, is stored and in which writing and reading of the computing unit is always possible, and a recovery area in which a duplicated copy or backup of the OS, a duplicated copy or backup of various types of application programs, and a duplicated copy or backup of user files are stored and in which the writing and reading of the computing unit is allowed only when the mode selection switch is in a recovery mode, when the mode selection switch is in the normal mode, access of the computing unit to the recovery area is completely blocked, and when the mode selection switch is in the recovery mode, the access of the computing unit to the recovery area is selectively allowed by the CPU and the duplicated copy or backup of the OS, the various types of application programs and the user files stored in the recovery area are provided to the computing unit. a central processing unit, CPU, which is separately equipped from the computing unit and configured to independently protect data stored in the auxiliary storage device independent of the computing unit and to independently monitor access to the data; a memory unit connected to the CPU; a storage medium unit connected to the CPU; an input and output, I/O device connected to the CPU; a mode selection switch which is connected to the I/O device and configured to select any one of a normal mode and a recovery mode by providing a permission signal in hardware; and a communication interface unit configured to provide a connection between the CPU and the computing unit, wherein the storage medium unit comprises a user area in which an operating system, OS, is stored and in which writing and reading of the computing unit is always possible, and a recovery area in which a duplicated copy or backup of the OS, a duplicated copy or backup of various types of application programs, and a duplicated copy or backup of user files are stored and in which the writing and reading of the computing unit is allowed only when the mode selection switch is in a recovery mode, when the mode selection switch is in the normal mode, access of the computing unit to the recovery area is completely blocked, and when the mode selection switch is in the recovery mode, the access of the computing unit to the recovery area is selectively allowed by the CPU and the duplicated copy or backup of the OS, the various types of application programs and the user files stored in the recovery area are provided to the computing unit.