In AMODE 64 applications, exception handlers are registered using the __set_exception_handler() C runtime library function. When no exception handler is registered, program checks and ABENDs cause POSIX/ANSI signals to be raised. These signals can be caught by user-written signal catchers, where suitable recovery can be done. When an exception handler is registered, no signal is generated when a program check or ABEND occurs. Instead, the active exception handler is invoked. Since program checks and ABENDs do not generate signals, the blocked/unblocked/ignored/caught settings for SIGABND, SIGFPE, SIGILL, and SIGSEGV make no difference. When an exception handler is active, all non-program-check and non-ABEND signal processing still occurs as described by POSIX or ANSI. Only signals normally generated by program checks or ABENDs are suppressed.