A memory system includes a memory cell array having a plurality of memory sectors. Each memory sector includes a plurality of memory cells. The memory system further includes a controller configured to write data to the memory cell array in response to a writing signal. The controller is further configured to refresh a memory sector among the plurality of memory sectors each time a writing signal is provided. When N (N is a positive integer) memory cells are programmed, a programming current is less than or equal to about 0.75 mA*N.