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The term boot comes from the idea of lifting oneself by one's own bootstraps: [5] the computer contains a tiny program (bootstrap loader) which will load and run a program found on a boot device. This program may itself be a small program designed to load a larger and more capable program, i.e., the full operating system.
A bootable MBR device is defined as one that can be read from, and where the last two bytes of the first sector contain the little-endian word AA55h, [nb 6] found as byte sequence 55h, AAh on disk (also known as the MBR boot signature), or where it is otherwise established that the code inside the sector is executable on x86 PCs.
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. Once all the boot and system drivers have been loaded, the kernel starts the session manager (smss.exe), which begins the login process. After the user has successfully logged into the machine ...
INT 19h is called to initiate the boot process, and INT 18h was called to start Cassette BASIC from ROM when the boot process found that none of the possible boot devices was bootable. Originally, by hooking INT 18h, the network adapter ROM would try to boot from the network when all other boot devices (floppy drives, hard drives, etc.) had failed.
In these cases a computer can often be "redirected" to boot from a USB device through use of an initial bootable CD or floppy disk. [5] [6] [7] Some Intel-based Macintosh computers have limitations when booting from USB devices – while the Extensible Firmware Interface (EFI) firmware can recognize and boot from USB drives, it can do this only ...
Restart the computer • If you haven't recently restarted your computer or you don't restart your computer very often, we recommend that you restart the computer. This helps clear the internal memory (RAM), which often resolves many issues.
On many Allwinner systems on a chip (A10, A20, A64), the boot ROM either waits for a bootloader to be loaded through USB (if a specific PIN is high) or tries to boot on several peripherals in a fixed order. [5] Some Allwinner systems on a chip can verify the signature of the booloaders. [6] But most devices being manufactured are not configured ...
With UEFI, it is possible to store product keys for operating systems such as Windows, on the UEFI firmware of the device. [21] [22] [23] UEFI is required for Secure Boot on devices shipping with Windows 8 [24] [25] and above. It is also possible for operating systems to access UEFI configuration data. [26]