[TUHS] Re: Question about BSD disklabel history

On Tue, Jan 02, 2024 at 03:48:28PM -0500, Dan Cross wrote: ACPI (Advanced Configuration and Power Interface) predates UEFI. ACPI was released in 1996, and was originally intended to be a replacement for APM (Advanced Power Management). With APM, the OS would crowbar itself into x86 Real mode in order to call into the APM BIOS in order to suspend the laptop, fetch power management events from the APM, etc. Later on, APM grew 32-bit protected mode interfaces, but effectively, the OS would completely lose control of the thread of execution while running APM BIOS code, which made life "exciting" for OS engineers. So ACPI was originally intended to solve a problem, where the OS could incorporate a byte code interpreter to do those things that would be very hardware specific (for example, how to diddle the various random I/O ports on a HP laptop to bring the perpipherals into a low power state, which of course would be completely different on a Dell or IBM laptop. Previously, the APM bios was the abstraction layer; ACPI was the new abstraction layer. UEFI came later. UEFI was the second system disease replacement for EFI (extensible firmware interface), which Intel had developed. EFI was an implementation that attempted to retain full backwards compatibility with the de factor standard originally established by the IBM BIOS. UEFI was an attempt to completely rework the interface between the OS boot code (which before would talk to the BIOS interface) with the all new singing, all dancing UEFI interface. Being a second system, of course it was made horribly complicated, so as to meet all of the requirements that might be dreamed up by the industry committee that put it together. Normally, once the OS has gotten to a certain point in its OS initialization, the OS can "terminate UEFI services". At that point, the OS can no longer call into the UEFI functions --- but it also doesn't have to worry about the UEFI code servicing an interrupt take taking control of the CPU away from the OS. However, the OS can still execute various ACPI functions, assuming the OS has its own AML interpreter. (Of course, the UEFI BIOS has its own AML interpreter --- and scheduler --- and everything else that a simple OS might have.) Ron Minnich has a number of really good presentations about the "joys" of working with UEFI. See the YouTube video, "Replace your Expoit-ridden Firmware with Linux"[1] and prepare to be horrified about what horrors lurks in the heart of UEFI.... [1] https://www.youtube.com/watch?v=iffTJ1vPCSo So you can very much be *not* using UEFI, and still be using ACPI --- either if you are using a pre-2004 computer, or if you are using a more modern platform which uses LinuxBoot. - Ted