AT> (PDS) A dATa set on an IBMmainframe thAT contains members, each of which acts like a separATe dATa set. Partitioned dATa sets are more space-efficient than individual dATa sets, because they can put more than one dATa set on a track. They are also used to hold libraries, with one function per member. The syntax for a member is NAME.OF.PDS(MEMBER) although some systems (such as Phoenix) could use NAME.OF.PDS:MEMBER Original PDSes were of fixed size, and needed frequent compression to recover space after deleting or changing members. Newer PDS/E Extended PDSes do not have this problem. (2003-12-05)