UEFIboot

UEFIboot refers to the process of starting a computer using the Unified Extensible Firmware Interface (UEFI) firmware and its associated boot ecosystem. Under UEFI, the firmware initializes hardware, reads boot entries stored in non-volatile RAM, and locates bootloaders on an EFI System Partition (ESP) on a GPT disk. The ESP contains one or more .efi executables, such as a boot manager or OS loader, which the UEFI firmware can execute directly, transferring control to the operating system.

Compared with traditional BIOS boot, UEFI supports 64-bit code, full pre-boot environments, and larger disk support through GUID Partition Table. It also enables faster startup, graphical or mouse-enabled boot menus, and features such as Secure Boot, which verifies bootloaders' signatures before execution. Boot entries can be managed by the firmware or by the OS using standard interfaces, and the mechanism to chain-load OS loaders is flexible, enabling multiple bootloaders to be installed on the ESP.

Common implementations include a Windows Boot Manager (Bootmgfw.efi), which loads Windows, Linux bootloaders such as GRUB2 (grubx64.efi), or systemd-boot (formerly gummiboot). Secure Boot works with authentication keys to prevent unauthorized code during early startup. Some systems also provide Compatibility Support Module (CSM) or legacy BIOS compatibility to boot non-UEFI systems, though pure UEFI boot is increasingly standard.