ACPI Specification Version 6.1 (January 2016, 6.2 MB, 1082 pages) [2]
All versions of the ACPI specification are available at: http://uefi.org/specifications [3]

Runtime BIOS Fixups for ACPI Tables (July 2013) [4]
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) [5]
Describes the Intel Processor driver capabilities bit definitions.

Processor Clocking Control Interface Specification (Version 1.0, 23 February 2009) [6]
Technical description of the Processor Clocking Control (PCC) Interface.

BIOS Boot Specification (Version 1.01, 11 January 1996) [7]
Technical description of how the BIOS should identify boot devices.

Multi-processor Startup for ARM Platforms (Version 1, 23 September 2014) (.docx) [8]
Protocol for starting multiple ARM processors.

Core System Resources Table - CSRT (November 14, 2011) (.doc) [9]
Definition of CSRT ACPI table for shared hardware functions.