The server program can create subspaces by issuing the IARSUBSP macro with the CREATE parameter. IARSUBSP CREATE allows you to name the subspaces yourself, have the system generate the subspace names, or have the system generate subspace names only when the name you provide is not unique within the address space. See the IARSUBSP macro description in z/OS MVS Programming: Authorized Assembler Services Reference EDT-IXG for more information about naming subspaces.

Be aware that, if you choose to let the system generate the subspace names for you, you must still supply three characters for the system to use.