The present invention provides a data storage device including a random access memory and a controller. The random access memory has a cache area. The controller loads a part of data mapping sets of the data mapping table on a plurality of sectors of the cache area, wherein any of the data mapping sets that has been read less than a predetermined number of times is defined as an infrequent data mapping set, and any of the data mapping sets that has been read more than the predetermined number of times is defined as a frequent data mapping set.