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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.
Before the operating system's first graphical screen is displayed, input and output are typically handled through BIOS. A boot menu such as the textual menu of Windows, which allows users to choose an operating system to boot, to boot into the safe mode, or to use the last known good configuration, is displayed through BIOS and receives ...
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.
It is located on fixed disks and removable drives, and must fit into the first 446 bytes of the Master Boot Record in order to leave room for the default 64-byte partition table with four partition entries and the two-byte boot signature, which the BIOS requires for a proper boot loader — or even less, when additional features like more than ...
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.
Some boot loaders can also load other boot loaders; for example, GRUB loads BOOTMGR instead of loading Windows directly. Usually, a default choice is preselected with a time delay during which a user can press a key to change the choice; after this delay, the default choice is automatically run so normal booting can occur without interaction.
The boot partition (or boot volume) [5] is the disk partition that contains the operating system folder, known as the system root or %systemroot% in Windows NT. [6]: 174 Before Windows 7, the system and boot partitions were, by default, the same and were given the "C:" drive letter.
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 ...