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 and which controls the non-volatile memory device. The operating method of the data storage device includes storing data in the buffer memory according to an external request, 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 determined program pattern.