EFI
also: UEFI, Unified EFI, Extensible Firmware Interface
EFI (Extensible Firmware Interface) is a modern firmware standard that replaces the legacy BIOS, providing a standardized interface between the operating system and hardware during boot.
EFI is a specification that defines how firmware communicates with the operating system before the kernel loads. Unlike BIOS, which is limited to 16-bit real mode and 1MB of addressable memory, EFI operates in 32-bit or 64-bit protected mode, allowing it to handle larger disks and more complex hardware initialization.
EFI systems use UEFI (Unified EFI, the modern standard) and boot from GPT (GUID Partition Table) partitions instead of MBR. The EFI firmware reads a bootloader from a special EFI System Partition (usually /boot/efi on Linux) formatted as FAT32.
Example: When you boot a modern Linux system with EFI, the firmware loads GRUB2 or another bootloader from /boot/efi/EFI/, which then loads the kernel. You can check if your system uses EFI by running [ -d /sys/firmware/efi ] && echo EFI || echo BIOS.