APM: Difference between revisions

The APM standard defines three interfaces through which it the APM BIOS and the operating system can communicate. They are the Real Mode Interface, the 16bit Protected Mode Interface, and the 32bit Protected Mode Interface. Only one of the interfaces may be in use at any given time. Before any of the interfaces can be used, the operating system must check if APM is actually supported (many very new computers don't support AMPAPM anymore) and if it is, connect to one of its interfaces. It is a good idea to send a disconnect command prior to connecting to an interface.