ACPI

[2] The specification is central to the Operating System-directed configuration and Power Management (OSPM) system.

Intel, Microsoft and Toshiba originally developed the standard, while HP, Huawei and Phoenix also participated later.

A reference AML interpreter implementation is provided by the ACPI Component Architecture (ACPICA).

At the BIOS development time, AML bytecode is compiled from the ASL (ACPI Source Language) code.

In 1999, then Microsoft CEO Bill Gates stated in an e-mail that Linux would benefit from ACPI without them having to do work and suggested to make it Windows-only.

[21] Other operating systems, including later versions of Windows, macOS (x86 macOS only), eComStation, ArcaOS,[22] FreeBSD (since FreeBSD 5.0[23]), NetBSD (since NetBSD 1.6[24]), OpenBSD (since OpenBSD 3.8[25]), HP-UX, OpenVMS, Linux, GNU/Hurd and PC versions of Solaris, have at least some support for ACPI.

[31] Once an OSPM-compatible operating system activates ACPI, it takes exclusive control of all aspects of power management and device configuration.

Function Fixed Hardware interfaces are platform-specific features, provided by platform manufacturers for the purposes of performance and failure recovery.

This includes RSDP, RSDT, XSDT, FADT, FACS, DSDT, SSDT, MADT, and MCFG, for example.

[44][45] The tables allow description of system hardware in a platform-independent manner, and are presented as either fixed-formatted data structures or in AML.

The AML can be decompiled by tools like Intel's iASL (open-source, part of ACPICA) for purposes like patching the tables for expanding OS compatibility.

[46][47] The Root System Description Pointer (RSDP) is located in a platform-dependent manner, and describes the rest of the tables.

The "It's now safe to turn off your computer" screen in Windows 9x. Most of the computer peripherals are offline, and the only ways to exit this screen are to power off or reset the computer.
The "It's now safe to turn off your computer" screen in Windows NT 4.0. Unlike Windows 9x and later NT releases, most of the essential computer peripherals are working normally, so the user can opt to restart instead of powering off their computer.
The "It's now safe to power off the system" screen in Windows 10 and 11.