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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 ...
When interrupt 19h is called, the BIOS attempts to locate boot loader software on a "boot device", such as a hard disk, a floppy disk, CD, or DVD. It loads and executes the first boot software it finds, giving it control of the PC. [28] The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches.
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 ...
For a warm boot, the BIOS will be located in the proper place in RAM and the northbridge will direct the reset vector call to the RAM. In earlier PC systems, before chipsets were standard, the BIOS ROM would be located at an address range that included the reset vector, and BIOS ran directly out of ROM.
Parts of coreboot becomes the systems BIOS and stays resident in memory after boot. Das U-Boot is a bootloader for embedded systems. It is used on systems that do not have a BIOS/UEFI but rather employ custom methods to read the bootloader into memory and execute it. Historical bootloaders, no longer in common use, include:
A QWERTY keyboard layout with the position of Control, Alt and Delete keys highlighted. Control-Alt-Delete (often abbreviated to Ctrl+Alt+Del and sometimes called the "three-finger salute" or "Security Keys") [1] [2] is a computer keyboard command on IBM PC compatible computers, invoked by pressing the Delete key while holding the Control and Alt keys: Ctrl+Alt+Delete.
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, winlogon applies User and Computer Group Policy setting and runs startup programs declared in the Windows Registry and in "Startup" folders.
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.