Open EFI File
An EFI file extension is a system file used by both Intel-based computing systems and Apple-based computing devices such as AppleTV.
The EFI file contains system-level data that runs between the operating system and the firmware.
Basically, an EFI file is an interface used to stage firmware updates, boot operating systems, and run pre-boot programs.
Using EFI files, systems can hand over the pre-boot process to a controlled environment.
EFI files are sometimes included with firmware updates and are loaded into the device's EFI system partition during the boot process.
In this case, the executable content of the EFI file safely executes the procedures necessary to update the device.
The EFI specification, originally developed by Intel, was evolved into the UEFI specification, which stands for "Unified Extensible Firmware Interface", thus becoming a standard.
The UEFI standard is maintained by the UEFI Forum.
Software for working with an EFI file
EFI files are developed and work with a Development Kit: