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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 ...
The boot code in the VBR can assume that the BIOS has set up its data structures and interrupts and initialized the hardware. The code should not assume more than 32 KB of memory to be present for fail-safe operation; [1] if it needs more memory it should query INT 12h for it, since other pre-boot code (such as f.e. BIOS extension overlays, encryption systems, or remote bootstrap loaders) may ...
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.
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 .
A bootable device can be storage devices like floppy disk, CD-ROM, USB flash drive, a partition on a hard disk (where a hard disk stores multiple OS, e.g Windows and Fedora), a storage device on local network, etc. [7] A hard disk to boot Linux stores the Master Boot Record (MBR), which contains the first-stage/primary bootloader in order to be ...
A modern PC's UEFI or BIOS firmware supports booting from various devices, typically a local solid-state drive or hard disk drive via the GPT or Master Boot Record (MBR) on such a drive or disk, an optical disc drive (using El Torito), a USB mass storage device (USB flash drive, memory card reader, USB hard disk drive, USB optical disc drive ...
A modern PC is configured to attempt to boot from various devices in a certain order. If a computer is not booting from the device desired, such as the floppy drive, the user may have to enter the BIOS Setup function by pressing a special key when the computer is first turned on (such as Delete, F1, F2, F10 or F12), and then changing the boot order. [6]
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.