Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide

LINKAGE

This suboption tells the compiler the default linkage to use when the LINKAGE suboption of the OPTIONS attribute or option for an entry has not been specified.

The compiler supports various linkages, each with its unique performance characteristics. When you invoke an ENTRY provided by an external entity (such as an operating system), you must use the linkage previously defined for that ENTRY.

As you create your own applications, however, you can choose the linkage convention. The OPTLINK linkage is strongly recommended because it provides significantly better performance than other linkage conventions.

Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide