BIOS interface/API

Recommended by Wim's BIOS...

Hi,

I'm studying x86 BIOS and I'm interested of what kind of power management functionalities/information is embedded into BIOS and what kind of interface there is in order to obtain this information?

Is there some kind of BIOS table containing processor specific information like supported operating voltages, frequencys etc? I know there is ACPI-BIOS that supports ACPI power management. I think all BIOSs should have a common basic structure, because Windows and Linux are working on the same hardware platform and are able to obtain the hardware specific information from the BIOS. But the question is where could I find information/standard what kind of information is actually embedded into BIOS? And how this information can be obtained by OS? Is it done by calling interrupts, or are the table contents mapped into memory? And is there some BIOS functions in addition to data tables?

Thank you very much in advance for any information!