This documentation is archived and is not being maintained.

UEFI Firmware

Updated: October 20, 2013

Applies To: Windows 8, Windows 8.1, Windows Server 2012, Windows Server 2012 R2

This section talks about things to consider when installing and deploying Windows on Unified Extensible Firmware Interface (UEFI)-based PCs.

When the PC starts, the firmware interface controls the booting process of the PC, and then passes control to Windows or another operating system.

UEFI is a replacement for the older BIOS firmware interface and the Extensible Firmware Interface (EFI) 1.10 specifications.

More than 140 leading technology companies participate in the Unified EFI Forum, including AMD, AMI, Apple, Dell, HP, IBM, Insyde, Intel, Lenovo, Microsoft, and Phoenix Technologies. For more info, see UEFI specifications.

Firmware that meets the UEFI 2.3.1 specifications provides the following benefits:

  • Faster boot and resume times.

  • Ability to use security features such as Secure Boot and factory encrypted drives that help prevent untrusted code from running before the operating system is loaded. For more information, see Secure Boot Overview and Factory Encrypted Drives.

  • Ability to more easily support large hard drives (more than 2 terabytes) and drives with more than four partitions.

  • Compatibility with legacy BIOS. Some UEFI-based PCs contain a Compatibility Support Module (CSM) that emulates earlier BIOS, providing more flexibility and compatibility for end users. To use the CSM, Secure Boot must be disabled.

  • Support for multicast deployment, which allows PC manufacturers to broadcast a PC image that can be received by multiple PCs without overwhelming the network or image server.

  • Support for UEFI firmware drivers, applications, and option ROMs.

Additional advantages are described in the Intel EFI and UEFI Overview and Specifications.

The following Windows editions include support for UEFI:

  • Windows 8.1 and Windows® 8 support native UEFI 2.0 or later on 32-bit (x86), 64-bit (x64), and ARM-based PCs. They also support BIOS-based PCs, and UEFI-based PCs running in legacy BIOS-compatibility mode.

    Some features such as Secure Boot require UEFI 2.3.1 Errata C or higher.

  • Windows Server 2012 R2 and Windows Server® 2012 support native UEFI 2.0 or later on 64-bit systems. Some features such as Secure Boot require UEFI 2.3.1.

  • Windows® 7, Windows Vista® with Service Pack 1 (SP1), Windows Server® 2008 R2 and Windows Server® 2008

    • Support UEFI 2.0 or later on 64-bit systems. They also support BIOS-based PCs, and UEFI-based PCs running in legacy BIOS-compatibility mode.

    • Support on Class 2 systems running in legacy BIOS-compatibility mode by using a CSM, so they can use the legacy BIOS INT10 features.

    • Are not supported on Class 3 systems, because these operating systems assume the presence of legacy BIOS INT10 support in the firmware, which is not available in a Class-3 UEFI implementation.

    • Windows Server® 2008 R2 and Windows Server® 2008 also support EFI 1.10 on Itanium-based systems.

  • While in UEFI mode, the Windows version must match the PC architecture. A 64-bit UEFI PC can only boot 64-bit versions of Windows. A 32-bit PC can only boot 32-bit versions of Windows. In some cases, while in legacy BIOS mode, you may be able to run 32-bit Windows on a 64-bit PC, assuming the manufacturer supports 32-bit legacy BIOS mode on the PC.

  • Windows supports a subset of the functionality that is defined in the UEFI specification. Windows implementations do not explicitly check against higher revisions of the firmware

  • For additional UEFI requirements, see UEFI Installation Media Format and default boot behavior and UEFI Requirements: Boot time, Runtime, Hibernation State (S4).

Before you install Windows on a UEFI-based PC, note the following:

  • For some platforms or hardware configurations, you may need to perform additional steps to make sure that Windows is installed in UEFI mode or in legacy BIOS-compatibility mode. For more information, see Boot to UEFI Mode or Legacy BIOS mode.

  • UEFI hard disks require the GUID partition table (GPT) partition structure, instead of the master boot record (MBR) partition structure that is used in BIOS.

    When you install Windows by using the Windows product DVD, Windows Setup detects whether the PC was booted in UEFI mode or BIOS-compatibility mode, and it configures Windows based on this selection.

    For information about preconfiguring GPT partitions, see Hard Drives and Partitions Overview.

  • Windows Preinstallation Environment (Windows PE) can be configured to support both UEFI mode and BIOS-compatibility mode.

    While the PC is in UEFI mode, the Windows PE version must match the PC architecture. A PC in 64-bit UEFI firmware mode can only boot 64-bit versions of Windows PE. A PC in 32-bit UEFI firmware mode can only boot 32-bit versions of Windows PE. On PCs that support both UEFI mode and legacy BIOS mode, you may be able to run 32-bit Windows PE on a 64-bit PC by changing BIOS menu settings from “UEFI mode” to “BIOS mode”, assuming the manufacturer supports legacy BIOS mode.

    For instructions, see WinPE: Create USB Bootable drive or WinPE: Install on a Hard Drive (Flat Boot or Non-RAM).

  • Note to firmware manufacturers: Do not use tools or applications to alter Windows-specific boot files, including files in the C:\boot and C:\EFI folders. Altering these files could interfere with the PC’s ability to boot up, to resume from hibernation, or to run system recovery tools. Instead, use tools such as BCDboot to set the boot order. For more info, see BCDboot Command-Line Options.