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

(NON)CONNECTED

The DEFAULT(NONCONNECTED) option indicates that the compiler assumes that any aggregate parameters are NONCONNECTED. References to elements of NONCONNECTED aggregate parameters require the compiler to generate code to access the parameter's descriptor, even if the aggregate is declared with constant extents.

The compiler does not generate these instructions if the aggregate parameter has constant extents and is CONNECTED. Consequently, if your application never passes nonconnected parameters, your code is more optimal if you use the DEFAULT(CONNECTED) option.

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