A memory device includes a memory array, a bit line driving circuit, a word line driving circuit, a read/write circuit, a controller, and a reference driving circuit. The memory array includes several memory units. The bit line driving circuit is configured to interpret a memory bit address and to drive a bit line. The word line driving circuit is configured to interpret a memory word address and to drive a word line. The read/write circuit is configured to read, set, or reset the memory units. The controller is configured to switch the memory array to work in a single memory unit mode or a dual memory unit mode. The reference driving circuit is configured to drive a reference line, wherein the reference line comprises several reference units, and the reference line and the reference units are located in the memory array.