A method of operating a memory controller is provided. The method includes determining a data state based on an input stream including multiple alphabet letters, converting a part of the input stream, which corresponds to a conversion size, into alphabet letters in a lower numeral system when the data state is determined to be a first state among multiple predetermined data states, inserting one of the converted alphabet letters into the input stream, and outputting each of the alphabet letters in the input stream as is when the data state is determined to be a second state among the predetermined data states.