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Furthermore, on a modern x86 system, BIOS calls can only be performed in Real mode, or Virtual 8086 mode. v8086 is not an option in Long mode. This means that a modern operating system, which operates in Protected mode (32 bit), or Long mode (64 bit), would need to switch into real mode and back to call the BIOS - a hugely expensive operation.
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 ...
In all versions of Windows 9x except ME, it is also possible to load Windows by booting to a DOS prompt and typing "win". There are some command line switches that can be used with the WIN command: with the /D switch, Windows boots to safe mode, and with the /D:n switch, Windows boots to safe mode
Safe Mode with Command Prompt (/SAFEBOOT:MINIMAL(ALTERNATESHELL) /SOS /BOOTLOG /NOGUIBOOT) – Default mode, except that Cmd.exe starts instead of Windows Explorer. [ 11 ] Windows in Directory Services Restore Mode ( /SAFEBOOT:DSREPAIR /SOS ) – (This mode is valid only for Windows-based domain controllers.)
RMM.PDR - Real Mode Mapper Virtual Device; The system may also use CONFIG.SYS, which contains settings and commands executed before loading the command interpreter and AUTOEXEC.BAT, which is a batch file automatically executed after loading COMMAND.COM.
Under real mode operating systems, such as DOS, calling INT 13h would jump into the computer's ROM-BIOS code for low-level disk services, which would carry out physical sector-based disk read or write operations for the program. In DOS, it serves as the low-level interface for the built-in block device drivers for hard disks and floppy disks.
In computing, BIOS (/ ˈ b aɪ ɒ s,-oʊ s /, BY-oss, -ohss; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the booting process (power-on startup). [1]
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.