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Such an option ROM would hook INT 19h, the BIOS boot interrupt, to preempt the BIOS boot loader and substitute their own boot loader. The boot loader on the option ROM would attempt to boot from a disk, network, or other boot program source attached to or installed on the adapter card; if that boot attempt failed, it would pass control to the ...
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.
Early BIOS versions did not have passwords or boot-device selection options. The BIOS was hard-coded to boot from the first floppy drive, or, if that failed, the first hard disk. Access control in early AT-class machines was by a physical keylock switch (which was not hard to defeat if the computer case could be opened).
Version 1 of the Desktop Management BIOS (DMIBIOS) specification was produced by Phoenix Technologies in or before 1996. [5] [6] Version 2.0 of the Desktop Management BIOS specification was released on March 6, 1996 by American Megatrends (AMI), Award Software, Dell, Intel, Phoenix Technologies, and SystemSoft Corporation. It introduced 16-bit ...
BIOS POST card for ISA bus BIOS POST card for PCI bus Professional BIOS POST card for PCI bus Two POST seven-segment displays integrated on a computer motherboard. The original IBM BIOS made POST diagnostic information available by outputting a number to I/O port 0x80 (a screen display was not possible with some failure modes). Both progress ...
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.
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 ...
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 ...