(PDS) A data set on an IBM mainframe 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.