1. A protective circuit for protecting hard disk data, comprising: a first hard disk (HD) coupling connected to a hard disk (HD) coupling of motherboard; a second HD coupling connected to a HD; a HD signal processor coupled to the first HD coupling, the second HD coupling, and a microprocessor; a random access memory (RAM) connected to the microprocessor; a nonvolatile semiconductor memory having program codes for converting a read/write instruction of the HD coupling on the motherboard with respect to the HD from a main data space to a virtual data space thereof; and the microprocessor for running the program codes; wherein if data stored in the virtual data space are damaged, the protective circuit of this invention can be applied to recopy the data in the main data space to the virtual data space to revive the latter.