Abstract: The present invention sorts very large volumes of data records by forming successive lists of sorted record start address by character rank from a LSD (least significant digit) of a sort field to a MSD (most significant digit) of such field with each list being formed in the order of the preceeding list. The present invention forms the lists by placing record start addresses in a collated list of virtual pockets wherein successive occurrences of like characters are linked to the next pocket memory position of such character so as to form the list in a memory requiring only the same number of addresses as there are records being sorted. The invention thus very materially reduces the size of pocket memory required for this type of data sorting.