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Unlike the legacy PC BIOS, UEFI does not rely on boot sectors, defining instead a boot manager as part of the UEFI specification. When a computer is powered on, the boot manager checks the boot configuration and, based on its settings, then executes the specified OS boot loader or operating system kernel (usually boot loader [ 62 ] ).
Prior to the development and ubiquitous adoption of the Plug and Play BIOS standard, an add-on device such as a hard disk controller or a network adapter card (NIC) was generally required to include an option ROM in order to be bootable, as the motherboard BIOS did not include any support for the device and so could not incorporate it into the BIOS's boot protocol.
The BIOS boot partition is a partition on a data storage device that GNU GRUB uses on legacy BIOS-based personal computers in order to boot an operating system, when the actual boot device contains a GUID Partition Table (GPT). Such a layout is sometimes referred to as BIOS/GPT boot.
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]
When GRUB is installed on a hard disk, boot.img is written into the boot sector of that hard disk. boot.img has a size of only 446 bytes. A boot sector is the sector of a persistent data storage device (e.g., hard disk , floppy disk , optical disc , etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed ...
BIOS interrupt calls perform hardware control or I/O functions requested by a program, return system information to the program, or do both. A key element of the purpose of BIOS calls is abstraction - the BIOS calls perform generally defined functions, and the specific details of how those functions are executed on the particular hardware of the system are encapsulated in the BIOS and hidden ...
UEFI support in Windows began in 2008 with Windows Vista SP1. [22] The Windows boot manager is located at the \EFI\Microsoft\Boot\ subfolder of the EFI system partition. [23] On Windows XP 64-Bit Edition and later, access to the EFI system partition is obtained by running the mountvol command. Mounts the EFI system partition on the specified drive.
Typically, the system firmware (UEFI or BIOS) will allow the user to configure a boot order. If the boot order is set to "first, the DVD drive; second, the hard disk drive", then the firmware will try to boot from the DVD drive, and if this fails (e.g. because there is no DVD in the drive), it will try to boot from the local hard disk drive.