A data storage device includes a non-volatile memory device which includes a memory cell array; and a memory controller which includes a buffer memory. The operating method of the data storage device includes storing data in the buffer memory, and determining whether the data stored in the buffer memory is data accompanying a buffer program operation of the memory cell array. When the data stored in the buffer memory is data accompanying the buffer program operation, the method further includes determining whether a main program operation on the memory cell array is required, and when a main program operation on the memory cell array is required, determining a program pattern of the main program operation on the memory cell array. The method further includes issuing a set of commands for the main program operation on the memory cell array to the multi-bit memory device based on the program pattern.