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

System facilities

The operating system offers error-handling facilities. Various situations can cause a machine interrupt, resulting in an entry to the system supervisor. The PL/I control program can use specified routines to define the action that is taken after any of these interrupts. Alternatively, the PL/I control program passes control to ON-units specified by the PL/I programmer.

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