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Example of an active Secure Boot as detected by rEFInd boot manager. The UEFI specification defines a protocol known as Secure Boot, which can secure the boot process by preventing the loading of UEFI drivers or OS boot loaders that are not signed with an acceptable digital signature.
GRUB 2, elilo and systemd-boot serve as conventional, full-fledged standalone UEFI boot managers (a.k.a. bootloader managers) for Linux. Once loaded by a UEFI firmware, they can access and boot kernel images from all devices, partitions and file systems they support, without being limited to the EFI system partition.
BIOS and UEFI can not only load multiple operating systems from a non-volatile device, they can also initialize system hardware for the loaded operating systems. Examples of first-stage bootloaders include BIOS, UEFI, coreboot, Libreboot, and Das U-Boot.
If UEFI Secure Boot is supported, a "shim" or "Preloader" is often booted by the UEFI before the bootloader or EFI-stub-bearing kernel. [11] Even if UEFI Secure Boot is disabled this may be present and booted in case it is later enabled. It merely acts to add an extra signing key database providing keys for signature verification of subsequent ...
Examples of first-stage (hardware initialization stage) boot loaders include BIOS, UEFI, coreboot, Libreboot and Das U-Boot. On the IBM PC, the boot loader in the Master Boot Record (MBR) and the Partition Boot Record (PBR) was coded to require at least 32 KB [ 51 ] [ 52 ] (later expanded to 64 KB [ 53 ] ) of system memory and only use ...
The architecture of the rootkit safeguard can also prevent the system from running the user's own software changes, which makes UEFI controversial as a legacy BIOS replacement in the open hardware community. Also, Windows 11 requires UEFI to boot, [87] with the exception of IoT Enterprise editions of Windows 11. [10]
The GUID Partition Table is specified in chapter 5 of the UEFI 2.8 specification. [2] GPT uses 64 bits for logical block addresses, allowing a maximum disk size of 2 64 sectors. For disks with 512‑byte sectors, the maximum size is 8 ZiB (2 64 × 512‑bytes) or 9.44 ZB (9.44 × 10²¹ bytes). [ 1 ]
An example is Rockbox as a firmware replacement for portable media players. There are many homebrew projects for various devices, which often unlock general-purpose computing functionality in previously limited devices (e.g., running Doom on iPods ).