Many system macros have the same name under different systems, but generate different object code and have different parameters. For example, the OPEN, CLOSE, GET, and PUT macros have the same name on z/OS and z/VSE but generate different object code.

Wherever the assembled program uses system macros, the system macros for the target system must be used when the program is assembled.

For example, when the assembled program is to be run under z/VSE, the z/VSE system macros must be used, even if the program is assembled under CMS.

Ensure that the macros used during assembly are for the correct release of the operating system upon which the assembled program is to run.