The LDTM determines whether to use the ASCII or Unicode data movement mode for mappings that read from a flat file or relational source. The LDTM determines the data movement mode based on the character sets that the mapping processes. When a mapping processes all ASCII data, the LDTM selects the ASCII mode. In ASCII mode, the Data Integration Service uses use one byte to store each character, which can optimize mapping performance. In Unicode mode, the service uses two bytes for each character.