Boot to UEFI Mode or Legacy BIOS Mode

Boot into UEFI mode or legacy BIOS-compatibility mode when installing Windows from your USB, DVD, or network location.
If you install Windows using the wrong mode, you won’t be able to use the features of that firmware mode without reformatting the drive.

Applies To: Windows 8, Windows 8.1, Windows Server 2012, Windows Server 2012 R2 and the latest Windows 10

Select the firmware mode during bootup

Boot the PC. As the firmware starts to run, press the key that opens the boot device menu. For example, press the Esc, F2, F9, F12, or other key to enter the firmware or boot menus.

On the boot device menu, select the command that identifies both the firmware mode and the device. For example, select UEFI USB Drive or Network - BIOS.

Note:
You might see separate commands for the same device. For example, you might see UEFI USB Drive and BIOS USB Drive. Each command uses the same device and media, but boots the PC in a different firmware mode.

If a boot device option does not appear for your device:

Check the options in the firmware menus to enable or disable BIOS-compatibility mode.
To use BIOS-compatibility mode, check for options in the firmware menus to disable UEFI SecureBoot features.
For older PCs (Windows® 7-era or earlier), look for options to Boot from file, and browse to the \EFI\BOOT\BOOTX64.EFI file on that device.

When you boot Windows PE on a UEFI PC, you may need to check whether the PC is booted in UEFI mode or legacy BIOS-compatibility mode.
For example, running Windows Setup through Windows PE requires you to be in the correct firmware mode.Use any of these methods to help make sure that Windows is installed using the correct firmware mode
For many operations, such as applying Windows images using Diskpart and DISM, the firmware mode might not make a difference.

If you install Windows by using Windows Setup or the Windows installation DVD or Bootable USB drive, use preformatted hard drive on your destination PCs
Use the GPT file format for UEFI mode or MBR file format for BIOS mode.

When Windows Setup runs, if the PC is booted to the wrong mode, Windows will fail to install. For more info, see Windows Setup: Installing using the MBR or GPT partition style. If this is a frequent problem, you can remove the boot files for UEFI mode or BIOS mode to prevent the PC from booting in the wrong mode. If the PC firmware is set up to boot in the wrong mode, the media will immediately fail to boot, allowing you to immediately retry booting the PC into the correct mode.
You can remove the UEFI or BIOS boot files from either Windows PE or Windows Setup. For example, if you only include boot files for UEFI mode on the Windows installation DVD, and during manufacturing you accidentally attempt to boot the PC to BIOS mode, the PC will immediately fail to boot, and you can begin troubleshooting right away.
- UEFI: To prevent Windows Setup or Windows PE from booting in BIOS mode, remove the bootmgr file on the root of the media.
- BIOS: To prevent Windows Setup or Windows PE from booting in UEFI mode, remove the efi folder on the root of the media.
From Windows PE, you can check the GetFirmwareEnvironmentVariable function. For more info, see WinPE: Boot in UEFI or legacy BIOS mode.
What is UEFI?
Applies to Windows 8.1, Windows RT 8.1 and Windows 10

UEFI (Unified Extensible Firmware Interface) is a standard firmware interface for PCs, designed to replace BIOS (basic input/output system). This standard was created by over 140 technology companies as part of the UEFI consortium, including Microsoft. It's designed to improve software interoperability and address limitations of BIOS. Some advantages of UEFI firmware include:
- Better security by helping to protect the pre-startup—or pre-boot—process against bootkit attacks.
- Faster startup times and resuming from hibernation.
- Support for drives larger than 2.2 terabytes (TB).
- Support for modern, 64-bit firmware device drivers that the system can use to address more than 17.2 billion gigabytes (GB) of memory during startup.
- Capabililty to use BIOS with UEFI hardware.
Note:

        All 64-bit versions of PCs running Windows with a logo from the Windows Certification Program will use UEFI instead of BIOS. To learn more about your PC's support of UEFI, see the product info that came with your PC.

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Switching from BIOS to UEFI

The UEFI interface is much better looking than the old BIOS screen (a sample of an old BIOS is shown below), but I have found it to be a bit slower in use. Quickest navigation is by mouse, but my system is not always responsive to mouse clicks. This isn’t a major issue as I spend very little time in the UEFI, and the other benefits are huge.

In addition to better interoperability, UEFI firmware provides several technical advantages:
- Compatibility with operating systems that support only BIOS
- Ability to boot from large disks
- CPU-independent architecture
- CPU-independent drivers
- Flexible pre-OS environment
- Modular design
Two of the most notable Windows features for UEFI systems are the following:
- Multicast deployment, which enables large scale network-based image deployment in manufacturing and enterprise settings.
- Fast boot and resume from hibernation, which improves user experience.
The rich UEFI interface provides ample room for innovation in the development of operating system features. Along with the other members of the Unified EFI Forum, Microsoft is investigating the following:
- Rootkit prevention
- Network authentication
UEFI Support
Operating systems started to support the platform interface design by 2007, but most Windows versions, such as Vista with SP1 and Windows Server 2008, only offered support on the 64-bit editions. Unfortunately, we found that industry support for UEFI is still very weak, and there are some shortcomings on the storage end.

OLD BIOS

Check whether the PC is booted in UEFI mode or legacy BIOS-compatibility mode.
Here is an OLD BIOS (blue Screen) UEFI mode is name as Secure Boot ..

For most PCs, you can disable Secure Boot through the PC’s BIOS.

You may need to disable Secure Boot to run some PC graphics cards, hardware, or operating systems such as Linux or previous version of Windows.

Secure Boot helps to make sure that your PC boots using only firmware that is trusted by the manufacturer.

For most PCs, you can disable Secure Boot through the PC’s firmware (BIOS) menus. For logo-certified Windows RT 8.1 and Windows RT PCs, Secure Boot is required to be configured so that it cannot be disabled.

ASUS EFI

Gigabyte New UEFI

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