A method of operating a data processing system includes compressing a first part of uncompressed data, and determining whether to compress a second part of the uncompressed data based on an expected data size of the compressed first part and an actual data size of the compressed first part. The method further includes transmitting one of first transmission data and second transmission data to an external memory device based on a result of the determining. The first transmission data includes the compressed first and second parts, and the second transmission data includes the first and second parts of the uncompressed data.