A memory device includes a storage unit array and a controller. The storage unit array contains storage units arranged in M rows and N columns and has M word lines and N bit line pairs. Each of the N bit line pairs includes a bit line and a source line. In operation, after obtaining Q rows of data that are to be written into Q rows of storage units in the storage unit array, the controller writes a first value into each of storage units in a column j in P columns of storage units. The controller then determines to-be-written rows in the Q rows of data, and writes in parallel a second value into each of storage units of the to-be-written rows in the storage units in the column j.