Extensible Firmware Interface File
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What is an EFI file?
An EFI file is a system file used by Intel-based computer systems and computer devices such as AppleTVs. It contains system-level data that executes between the operating system and the firmware. EFI files are used for staging firmware updates, booting operating systems, and running pre-boot programs.
Using EFI files, systems can hand off the pre-boot process to a controlled environment. For example, EFI files are sometimes included with firmware updates and are loaded into the device's EFI System partition during the boot process. Here, the executable content in the EFI file safely runs the procedures necessary to update the device.
When you start a PC that does not yet have an installed operating system, the PC searches its disc drives and connected media for an EFI file it can use to boot and install an operating system. For example, the Windows 10 installation package contains the following EFI files, which your PC will search for as it begins installing Windows 10:
NOTE: The EFI specification, originally developed by Intel, was updated to the UEFI specification, which stands for "Unified Extensible Firmware Interface." The UEFI standard is maintained by the UEFI Forum.
How to open an EFI file
Typically, EFI files are not meant to be opened. Hardware developers and other advanced PC users can open EFI files using the EFI Developer Kit (cross-platform).