ACPI Specification Version 6.1 (January 2016, 6.2 MB, 1082 pages)
All versions of the ACPI specification are available at: http://uefi.org/specifications
Runtime BIOS Fixups for ACPI Tables (July 2013)
Describes methods for the BIOS to perform runtime modifications to ACPI tables before handoff to the OS.
Intel Processor Vendor-Specific ACPI: Interface Specification (December 2014)
Describes the Intel Processor driver capabilities bit definitions.
Processor Clocking Control Interface Specification (Version 1.0, 23 February 2009)
Technical description of the Processor Clocking Control (PCC) Interface.
BIOS Boot Specification (Version 1.01, 11 January 1996)
Technical description of how the BIOS should identify boot devices.
Multi-processor Startup for ARM Platforms (Version 1, 23 September 2014) (.docx)
Protocol for starting multiple ARM processors.
Core System Resources Table - CSRT (November 14, 2011) (.doc)
Definition of CSRT ACPI table for shared hardware functions.