uefi EFI files, most commonly referred to as, Extensible Firmware Interface files, are a type of file extension most commonly used for creating an environment in order to boot up the OS. EFI file extensions are usually hidden in the OS in a special EFI system partition and are considered to be UEFI boot loaders. EFI files exist in UEFI file systems and contain data which dictates, how the boot process should occur, or how the booting phases should be executed/initiated. The EFI format was originally developed in the 1990s when the first generation of the Intel HP Itanium systems were being built. It was designed as part of the "Intel Boot Initiative" to tackle server platforms which were large in size; later on, it came to be known as the "Extensible Firmware Interface (EFI)"