Rational Developer for System z
Enterprise COBOL for z/OS, Version 4.1, Programming Guide


Dynamic link libraries (DLLs)

A DLL is a load module or a program object that can be accessed from other separate load modules.

A DLL differs from a traditional load module in that it exports definitions of programs, functions, or variables to DLLs, DLL applications, or non-DLLs. Therefore, you do not need to link the target routines into the same load module as the referencing routine. When an application references a separate DLL for the first time, the system automatically loads the DLL into memory. In other words, calling a program in a DLL is similar to calling a load module with a dynamic CALL.

This image is a block diagram that shows module and DLL relationships. Link to detail.

A DLL application is an application that references imported definitions of programs, functions, or variables.

Although some functions of z/OS DLLs overlap the functions provided by COBOL dynamic CALL statements, DLLs have several advantages over regular z/OS load modules and dynamic calls:

DLLs are supported by IBM z/OS Language Environment, based on function provided by the z/OS program management binder. DLL support is available for applications running under z/OS in batch or in TSO, CICS, UNIX, or IMS environments.

related references  
PGMNAME  
MVS Program Management: User's Guide and Reference (Binder support for DLLs)


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