The Legac-e Information Site

Introduction

The quality gurus of the 1980s preached the benefits of solving small problems rather than large ones by encouraging people to avoid "eating the elephant" or "boiling the ocean".

This was not a new concept to programmers who a decade earlier had begun to break large programs into smaller units by adopting a technique known as Modular Programming.

Combining multiple modules into a composite program was one of the roles of the Linkage Editor (program name IEWL), which is now known as the Program Binder (program name HEWL).

Introduction

By definition internal sub-routines are part of the program entity both at a source and object level and there are no additional issues to consider. In this context internal sub-routines are those invoked with BAS/BASR in Assembler or PERFORM in COBOL.

External sub-routines will be invoked by CALL/LINK/XCTL in Assembler or CALL in COBOL.

With external sub-routines there is a choice as to whether to combine them into a single loadable program, which is the responsibility of the Linkage Editor/Program Binder, or to allow the sub-routines to be loaded independantly which is known as Dynamic Linkage.

Even with the Dynamic Linkage option, the Linkage Editor/Program Binder is still required after the compile stage to ensure that the machine readable code is executable.

Further reading associated with this module should include:

• " z/OS MVS Program Management: User's Guide and Reference".