What Is an EFI File?

EFI Files Are UEFI Boot Loaders and Here's How They Work

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A file with the EFI file extension is an Extensible Firmware Interface file. These files are boot loader executables, exist on UEFI (Unified Extensible Firmware Interface) based computer systems, and contain data on how the boot process should proceed.

On a system with an installed operating system, the boot manager that exists as part of the motherboard UEFI firmware will have an EFI file location stored in the BootOrder variable.

This might actually be another boot manager if you have an installed multi-boot tool but is usually just the EFI boot loader for your operating system.

Most of the time, this EFI file is stored on a special EFI system partition. This partition is usually hidden and does not have a drive letter.

On a UEFI system with Windows 10 installed, for example, the EFI file will be located at the following location, on that hidden partition:

\EFI\boot\bootx64.efi

or

\EFI\boot\bootia32.efi

Note: You'll see the bootx64.efi file if you have a 64-bit version of Windows installed or the bootia32.efi file if you're using a 32-bit version. See 64-bit & 32-bit: What's the Difference? for more on this if you're not sure.

On some Windows computers, the winload.efi file acts as the boot loader and is usually stored in the following location:

C:\Windows\System32\Boot\winload.efi

Note: If your system drive is something other than C or Windows is installed to a folder other than Windows, then the exact path on your computer will differ respectively, of course.

On a system without an installed operating system, with a blank BootOrder variable, the motherboard's boot manager looks in predefined places for an EFI file, like on discs in optical drives and on other connected media. This occurs because, if that field is empty, you don't have a working OS installed and so you're likely going to install one next.

For example, on a Windows 10 installation DVD or ISO image, the following two files exist, which your computer's UEFI boot manager will quickly locate:

D:\efi\boot\bootx64.efi

and

D:\efi\boot\bootia32.efi

Note: Like with the Windows installation drive and path from above, the drive here will be different depending on the media source. In this case, D is the letter assigned to my optical drive. Additionally, as you may have noticed, both 64-bit and 32-bit EFI boot loaders are included on the installation media. This is because the install disc contains both architecture types as installation options.

More Information on EFI Files

EFI files can be opened with EFI Developer Kit and Microsoft EFI Utilities but frankly, unless you're a hardware developer, there's little use in "opening" an EFI file.

Here are some of the default EFI file locations for some non-Windows operating systems:

macOS uses the following EFI file as its boot loader but not in all situations:

\System\Library\CoreServices\boot.efi

The EFI boot loader for Linux will differ depending on the distribution you have installed, but here are a few:

\EFI\SuSE\elilo.efi
\EFI\RedHat\elilo.efi
\EFI\ubuntu\elilo.efi

You get the idea.

If you have more questions about EFI files, see my Get More Help page or information about contacting me on social networks or via email, posting on tech support forums, and more.