Secondary storage device using nonvolatile semiconductor memory

A secondary storage device using a nonvolatile semiconductor memory which permits rewriting of data on a block area-by-block area basis and is provided with spare block areas, comprising:

• logical-physical correspondence storing means for storing correspondence between logical block numbers identifying respective pieces of information to be stored and physical block numbers identifying respective block areas constituting the nonvolatile semiconductor memory;
• first writing means, responsive to a request to write information accompanied by a logical block number, for writing into a spare first block area the information with respect to which the write request has been made;
• physical block number reading means for referring to said logical-physical correspondence storing means to read out a physical block number corresponding to the logical block number accompanying the information with respect to which the write request was made;
• first erasing means for erasing information stored in a second block area with the physical block number read out by said physical block number reading means and treating the second block area as a spare block area;
• first correspondence modifying means for associating the physical block number of a first block area with the logical block number accompanying the information with respect to which the write request was made, and for causing said logical-physical correspondence storing means to store a correspondence of thus-associated physical and logical block numbers;
• searching means for searching all block areas in the nonvolatile semiconductor memory except spare block areas for an alternate block area when a number of repetitions of erasure in the second block area has reached a predetermined reference value;
• second writing means for writing into the second block area information stored in the alternate block area located by said searching means;
• second correspondence modifying means for associating a physical block number of the second block area with the logical block number of the information stored in the alternate block area and causing said logical-physical correspondence storing means to store the correspondence of the thus-associated physical and logical block numbers;
• and
• second erasing means for erasing the information stored in the alternate block area and treating the alternate block area as a spare block area.