A memory device includes a plurality of memory modules and a plurality of control lines. Each memory module includes a plurality of memory units. Each memory unit includes: a plurality of memory cell groups, each of which includes at least one memory cell; a plurality of first bit lines, each of which is coupled to the at least one memory cell of a respective memory cell group; a second bit line; and a plurality of controllable circuits, each of which has an input terminal coupled to a respective first bit line, an output terminal coupled to the second bit line, and a control terminal. Each control line is coupled to the control terminal of a corresponding controllable circuit of each of at least one memory unit of each memory module. The memory device consumes relatively small power.