There are many variations of linked lists. We can make the list into a circular list, or ring, by changing the link of the last record from zero to the address of the first record in the list. Now we can reach every item in the list starting at any item in the list. Figure H-7(a) shows a circular list for the StudentNumber order. A two-way linked list has links in both directions. In Figure H-7(b), a two-way linked list has been created for both ascending and descending student orders.
Records ordered using linked lists cannot be stored on a sequential file because some type of direct-access file organization is needed to use the link values. Thus, either indexed sequential or direct file organization is required for linked-list processing.