UEFI
also: EFI, Unified Extensible Firmware Interface
UEFI (Unified Extensible Firmware Interface) is a modern firmware standard that initializes hardware and boots the operating system, replacing the older BIOS. It supports larger disks, secure boot, and faster startup times.
UEFI is the firmware layer that runs before your operating system loads. It performs hardware initialization, device detection, and hands control to the bootloader. Unlike its predecessor BIOS, UEFI uses the GPT (GUID Partition Table) instead of MBR, allowing support for disks larger than 2TB and more than four primary partitions.
UEFI provides several modern features: Secure Boot (which verifies bootloader signatures to prevent malware), graphical boot menus, mouse support, and faster boot times. It also includes UEFI Shell, an interactive pre-boot environment for troubleshooting and system configuration.
When installing Linux, you'll typically choose between UEFI or Legacy BIOS mode. Most modern systems default to UEFI. You can check your system's boot mode on Linux with ls /sys/firmware/efi—if it exists, you're running in UEFI mode.