Disclosed is a memory system which includes a nonvolatile memory device including a memory cell array having a plurality of word lines including a first set of word lines storing first data having a high bit error rate, and a second set of word lines storing second data having low bit error rate less than the high bit error rate, and a memory controller that during a program operation maps logical addresses for a portion of the first data and a portion of the second data onto a selected word line selected from the plurality of word lines.