Data storage device and operating method for flash memory

A data storage device and operating method for a FLASH memory are disclosed. The data storage device includes a FLASH memory and a controller. The FLASH memory includes a first block and a second block. The first and second blocks each includes a plurality of pages. The controller executes a firmware to determine whether a data segment from a host is a complete page segment. When the data segment is a complete page segment, the controller stores the data segment into the first block. When the data segment is an incomplete page segment, the controller stores the data into segment the second block.