Compiling and linking for running under IMS

For best performance in the IMS environment, use the RENT compiler option. It causes COBOL to generate reentrant code. You can then run your application programs in either preloaded mode (the programs are always in storage) or nonpreload mode, without having to recompile with different options.

IMS allows COBOL programs to be preloaded. This preloading can boost performance because subsequent requests for the program can be handled faster when the program is already in storage (rather than being fetched from a library each time it is needed).

You must use the RENT compiler option to compile a program that is to be run preloaded or as both preloaded and nonpreloaded. When you preload a program object that contains COBOL programs, all of the COBOL programs in that program object must be compiled with the RENT option.

In an application with any mixture of Enterprise COBOL, IBM® COBOL, and VS COBOL II programs, the following compiler options are recommended:

Table 1. Recommended compiler options for applications with mixed COBOL programs
Enterprise COBOL	IBM COBOL	VS COBOL II
RENT	RENT	RENT and RES

You can place programs compiled with the RENT option in the LPA or ELPA. There they can be shared among the IMS dependent regions.

To run beyond the 16-MB line, your application program must be compiled with RENT and RMODE(ANY).

With IMS, the data for IMS application programs can reside beyond the 16-MB line, and you can use DATA(31) and RENT for programs that use IMS services.

The recommended link-edit attributes for proper execution of COBOL programs under IMS are as follows:

Link as RENT program objects that contain only COBOL programs compiled with the RENT compiler option.
To link program objects that contain a mixture of COBOL RENT programs and other programs, use the link-edit attributes recommended for the other programs.