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UEFI requires the firmware and operating system loader (or kernel) to be size-matched; that is, a 64-bit UEFI firmware implementation can load only a 64-bit operating system (OS) boot loader or kernel (unless the CSM-based legacy boot is used) and the same applies to 32-bit.
Such an option ROM would hook INT 19h, the BIOS boot interrupt, to preempt the BIOS boot loader and substitute their own boot loader. The boot loader on the option ROM would attempt to boot from a disk, network, or other boot program source attached to or installed on the adapter card; if that boot attempt failed, it would pass control to the ...
Version 2.0 of the Desktop Management BIOS specification was released on March 6, 1996 by American Megatrends (AMI), Award Software, Dell, Intel, Phoenix Technologies, and SystemSoft Corporation. It introduced 16-bit plug-and-play functions used to access the structures from Windows 95. [7]
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.
On system with BIOS firmware, the BIOS invokes MBR boot code from a hard disk drive at startup. The MBR boot code and the VBR boot code are OS-specific. In Microsoft Windows, the MBR boot code tries to find an active partition (the MBR is only 512 bytes), then executes the VBR boot code of an active partition.
In Windows NT, the booting process is initiated by NTLDR in versions before Vista and the Windows Boot Manager (BOOTMGR) in Vista and later. [4] The boot loader is responsible for accessing the file system on the boot drive, starting ntoskrnl.exe, and loading boot-time device drivers into memory.
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 ...
Typical POST screen (AMI BIOS) Typical UEFI-compliant BIOS POST screen (Phoenix Technologies BIOS) Summary screen after POST and before booting an operating system (AMI BIOS) A power-on self-test ( POST ) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on.