The error and event reporting RTAS calls are designed to provide an abstract interface into hardware registers in the system that may contain correctable or non-correctable errors and to provide an abstract interface to certain platform events that may be of interest to the OS. Such errors and events may be detected either by a periodic scan or by an exception trap. These functions are not intended to replace the normal error handling in the OS. Rather, they enhance the OS’s abilities by providing an abstract interface to check for, report, and recover from errors or events on the platform that are not necessarily known to the OS. The OS uses the error and event RTAS calls in two distinct ways: Periodically, the OS calls event-scan to have the system firmware check for any errors or events that have occurred. Whenever the OS receives an interrupt or exception that it cannot fully process, it calls check-exception. The first case covers all errors and events that do not signal their occurrence with an interrupt or exception. The second case covers those errors and events that do signal with an interrupt or exception. It is platform dependent whether any specific error or event causes an interrupt on that platform. R1--1. RTAS must return the event generated by a particular interrupt or event source by either check-exception or event-scan, but not both. R1--2. check-exception and event-scan , on a 64-bit capable platform, must be able to handle platform resources that are accessed using 64-bit addresses when instantiated in 32-bit mode.