Most JES2 code in common storage resides above 16 megabytes in virtual storage, while all JES2 code in private storage resides below 16 megabytes in virtual storage. All JES2 code runs in 31-bit addressing mode, except those sections of JES2 code that deal with calls to restricted MVS™ services (such as the FSI). JES2 uses 31-bit addressing to reduce its use of the common storage area (CSA) below 16 megabytes in virtual storage.

Some JES2 control blocks reside below 16 megabytes in virtual storage, because these control blocks need to references other MVS control blocks that also reside there. (For a list of these control blocks, see z/OS JES2 Installation Exits.)

If you require further information on JES2 when operating in 31-bit addressing mode, to include coding specifics, control block residency, required linkage conventions, or the changes to several assembler instructions (to provide compatibility with the operating system code) see z/OS JES2 Installation Exits and z/OS MVS Programming: Assembler Services Guide.