When IBM® introduces a new version or a new release of an existing version, the new version or release supports all MVS™ macros from previous versions and releases. Programs assembled on an earlier level of MVS that issue macros will run on later levels of MVS.

In most cases, the reverse is also true. When you assemble programs that issue macros on a particular version and release of MVS, those programs can run on earlier versions and releases of MVS, provided you request only those functions that are supported by the earlier version and release. This is useful for installations that write applications that might be assembled on one level of MVS, but run on a different level.

As MVS supports new architectures, addressability changes. To take best advantage of the new architectures, some macros have more than one possible expansion. You are required to have the macro expand according to the environment in which the program runs. This topic is described in this introductory information.

The problem of compatibility is not the same as selecting a macro version through the PLISTVER parameter to ensure the correct parameter list size for a macro. For selecting a parameter list version number, see Specifying a macro version number.