A flash memory device includes physical pages that store data sectors therein. The method of operating the flash memory device includes receiving write data sectors to be stored in the flash memory device, pairing the write data sectors with write data sectors and with written data sectors previously stored in physical pages of the flash memory device based upon a matching and deduplication operation to define data sector pairs and a difference therebetween, and rewriting to the physical pages of the flash memory device, in a partial-page writing mode, to store the difference between the write data sector and its respective paired data sector. The partial-page writing mode is performed on a respective physical page after a previous programming and before erasing. The written data sectors included in the data sector pairs only partially occupy the corresponding physical page of the flash memory device. The difference between the write data sector and its respective paired data sector is stored in an unoccupied portion of the corresponding physical page of the flash memory device.