Within the z/OS operating system, the terms "partitioned data set", "partitioned data set/extension", and "library" are synonymous and refer to a type of data set that can be used for the storage of other data sets (usually programs in the form of source, object or load modules). A library must be stored on direct access storage and be wholly contained in one volume. It contains independent, consecutively organized data sets, called members. Each member has a unique name, not more than 8 characters long, which is stored in a directory that is part of the library. All the members of one library must have the same data characteristics because only one data set label is maintained.
You can create members individually until there is insufficient space left for a new entry in the directory, or until there is insufficient space for the member itself. You can access members individually by specifying the member name.
Use DD statements or their conversational mode equivalent to create and access members.
You can delete members by means of the IBM utility program IEHPROGM. This deletes the member name from the directory so that the member can no longer be accessed, but you cannot use the space occupied by the member itself again unless you recreate the library or compress the unused space using, for example, the IBM utility program IEBCOPY. If you attempt to delete a member by using the DISP parameter of a DD statement, it causes the whole data set to be deleted.