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Line 5: Information about ACPI is stored in the BIOS's memory (for those systems that support ACPI of course). There are 2 main parts to ACPI. The first part is the tables used by the OS for configuration during boot (these include things like how many CPUs, APIC details, NUMA memory ranges, etc). The second part is the run time ACPI environment, which consists of AML code (a platform ~~independant~~independent OOP language that comes from the BIOS and devices) and the ACPI SMM (System Management Mode) code. To begin using ACPI, the operating system must look for the RSDP (Root System Description Pointer). This is covered in [[RSDP]] because it is too verbose to put here. If the RSDP is found and the verification is valid, it contains a pointer to the RSDT (Root System Description Table) and for newer versions of ACPI (ACPI 2.0 and later) there is an additional XSDT (eXtended System ~~Desciption~~Description Table). Both the RSDT and the XSDT contain pointers to other tables. The only real difference between the RSDT and the XSDT is that the XSDT contains 64 bit pointer instead of 32 bit pointers. For the run time part of ACPI the main table to detect is the FADT (Fixed ACPI Description Table) as this contains information needed to enable ACPI.

ACPI: Difference between revisions

ACPI (view source)