System macro instructions are macro instructions provided by IBM for communicating service requests to the control program. You can use these instructions only when programming in assembler language. They are processed by the assembler program using macro definitions supplied by IBM and placed in the macro library when your control program was installed.

You can specify one of three system macro instructions to pass control to the program: LINK, ATTACH, or XCTL.

When you issue one of these instructions, the first load module of DFSORT is brought into main storage. The linkage relationship between your program and DFSORT differs according to which of the instructions you have used. For a complete description of the macro instructions and how to use them, refer to z/OS MVS Programming: Assembler Services Guide, z/OS MVS Programming: Assembler Services Reference ABE-HSP, and z/OS MVS Programming: Assembler Services Reference IAR-XCT.