AMODE and RMODE attributes

Every program that runs in z/OS is assigned two attributes, an AMODE (addressing mode) and an RMODE (residency mode):

AMODE: Specifies the addressing mode in which the program is designed to receive control. Generally, the program is also designed to run in that mode, although a program can switch modes and can have different AMODE attributes for different entry points within a program module.
z/OS uses a program's AMODE attribute to determine whether a program invoked using ATTACH, LINK, or XCTL is to receive control in 24-bit or 31-bit addressing mode.
RMODE: Indicates where the program can reside in virtual storage.
z/OS uses the RMODE attribute to determine whether a program must be loaded into virtual storage below 16 MB, or can reside anywhere in virtual storage (above or below 16 MB).

Valid AMODE and RMODE specifications are:

Attribute	Meaning
AMODE=24	24-bit addressing mode
AMODE=31	31-bit addressing mode
AMODE=64	64-bit addressing mode
AMODE=ANY	Either 24-bit or 31-bit addressing mode
RMODE=24	The module must reside in virtual storage below 16 MB. Use RMODE=24 for programs that have 24-bit dependencies.
RMODE=ANY	Indicates that the module can reside anywhere in storage, which includes addresses above the 16 megabyte line.

If you do not specify the AMODE or RMODE in the assembler program or when you link the program, both AMODE and RMODE default to 24.