systems and programs for improving the efficiency of a sorting process in a computer system are disclosed . data is provided in an input file external to the central processing unit of the computer system . in one embodiment , the implemented process involves investigating the contents of the input file in order to identify presorted portions thereof ; incorporating the identified presorted portions of the input file into a second file external to the central processing unit , performing this step by rearranging directory information , without physically transferring the presorted portions from the input file . in sort processes involving both a string generation phase and a merge phase , the techniques described may be used in either or both phases , as well as in any output phase . rearrange directory information rather than physically transferring data provides for greater efficiency in disk i / o .