When Start a Windows based Machine, when something goes wrong are there are multi boot option. There will be pop a UI whose title is Windows Boot Manager. And Windows 7/8/10 is an option in its list. However it is enough to prove that this software runs before the kernel of Windows OS launch. Then I can make a inference that Windows Boot Manager is not a Windows program.

Is my inference true?

Can it exsit without Windows OS? (For example let it replace GRUB on UNIX machine.)


Yes, bootloaders and boot managers are started directly by the firmware.

(Although some firmwares are so complex that you could practically call UEFI an "OS", and its bootloaders "UEFI programs"...)

  • Could Windows Boot Manager exist without Windows? Yes.
  • Could it replace GRUB? Maybe, maybe not. (Although it depends on what OS you mean by "UNIX"!) It would be easier on UEFI than on BIOS.
  • Could GRUB replace the Windows Boot manager? Maybe, maybe not. (Depends on the Windows version.)

The problem is that OS kernels have different ways of being started, and expect the bootloader to provide certain initial parameters, such as which disk to boot from, what "kernel commandline" to use, where the Linux initramfs is, and so on. For example, here's the Linux boot protocol, and here's the Multiboot spec used by some BSDs.

So you cannot tell Windows BOOTMGR to start vmlinuz directly, and you cannot tell GRUB to start ntoskrnl.exe directly.

However, sometimes that job isn't done by the boot manager itself, but instead by a small "stub" bootloader which can be started in a standard way. And that stub bootloader could be started by a different boot manager than usual.

  • For example, Windows BOOTMGR first starts winload.efi, and that's where all the preparations for starting ntoskrnl are done.

    This means that you can make GRUB boot Windows by starting winload.efi, without going through BOOTMGR.

  • Similarly, Linux kernels often come with a built-in "EFI stub", so that the kernel itself can be run as a standalone UEFI program.

    So if your Linux kernel has its own "EFISTUB" option enabled, or the systemd-boot stub attached, then you can make Windows BOOTMGR start it directly without using GRUB or anything else.

  • Thanks for answering, however what does "firmware" mean? Is it same meaning in any context? Does it just include UEFI?
    – pah8J
    Apr 14 '18 at 13:42
  • In this post it includes the BIOS (on IBM PC compatibles) and the UEFI (on modern PCs). Generally it could also mean OpenFirmware (on PowerPC systems) and ... whatever else other computer architectures use.
    – user1686
    Apr 14 '18 at 13:46

Actually both compliments each other.

Literal meaning of bootstrap is boot laces and in context of day to day life it means tie boot laces & ready to go, in relation to computing it means getting ready to work.

Bootstrap program or popularly know as booting is a boot loader, also called a Boot Manager, performs BIOS. Initiates all the attached peripherals and test them whether are functioning or not and the next is the bigger task to load the operating system.

Concisely, operating system makes the computer operational by all means.

Therefore I could say, without the booting an OS as well as the computer is helpless.

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