The invention provides a method for moving data internally, performed by a processing unit, including at least the following steps. The processing unit transmits partial copyback read commands to a storage sub-unit through an access interface, where each partial copyback read command is used to direct logic circuits of the storage sub-unit to store partial data of a page of the storage sub-unit in a designated location of a data buffer of the storage sub-unit. The processing unit further transmits a copyback write command to the storage sub-unit through the storage sub-unit for programming the data of the data buffer in a new page of the storage sub-unit.