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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.
Ventoy is a free and open-source utility used for creating bootable USB media storage devices with files such as .iso, .wim, .img, .vhd(x), and .efi.Once Ventoy is installed onto a USB drive, there is no need to reformat the disk to update it with new installation files; it is enough to copy the .iso, .wim, .img, .vhd(x), or .efi file(s) to the USB drive and boot from them directly.
The original motivation for EFI came during early development of the first Intel–HP Itanium systems in the mid-1990s. BIOS limitations (such as 16-bit real mode, 1 MB addressable memory space, [7] assembly language programming, and PC AT hardware) had become too restrictive for the larger server platforms Itanium was targeting. [8]
On Apple Mac computers using Intel x86-64 processor architecture, the EFI system partition is initially left blank and unused for booting into macOS. [13] [14]However, the EFI system partition is used as a staging area for firmware updates [15] and for the Microsoft Windows bootloader for Mac computers configured to boot into a Windows partition using Boot Camp.
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.
Also, Windows 11 requires UEFI to boot, [87] with the exception of IoT Enterprise editions of Windows 11. [10] UEFI is required for devices shipping with Windows 8 [88] [89] and above. Other alternatives to the functionality of the "Legacy BIOS" in the x86 world include coreboot and libreboot.
The GUID Partition Table is specified in chapter 5 of the UEFI 2.11 specification. [ 2 ] : 111 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 ]
For a cold boot, for example, it may need to execute all of its functionality. If, however, the system supports power saving or quick boot methods, the BIOS may be able to circumvent the standard POST device discovery, and simply program the devices from a preloaded system device table.