What is the boot file?


  1. Jonathan_King
    Posts : 13,354
    Windows 7 Professional x64
       New #1

    What is the boot file?


    I am wondering if someone could teach me a bit more about the MBR and boot loaders.

    The fact that it is so easy to put the installation files on a thumb drive confuses me. Essentially, all that needs to be done is marking the partition as active, and copying all the files to it.

    Let's start from the beginning. When the BIOS instructs the computer to boot from the USB drive, it looks at the MBR of the drive, right? How is there an MBR on the thumb drive? I did not install anything.

    I know that this is showing my complete misunderstanding.

    Next, after the machine is told to boot from the drive, what file does it look for? What is the critical file on the drive that starts the whole deal?

    ~JK
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  3. zigzag3143
    Posts : 28,845
    Win 8 Release candidate 8400
       New #2

    Jonathan_King said:
    I am wondering if someone could teach me a bit more about the MBR and boot loaders.

    The fact that it is so easy to put the installation files on a thumb drive confuses me. Essentially, all that needs to be done is marking the partition as active, and copying all the files to it.

    Let's start from the beginning. When the BIOS instructs the computer to boot from the USB drive, it looks at the MBR of the drive, right? How is there an MBR on the thumb drive? I did not install anything.

    I know that this is showing my complete misunderstanding.

    Next, after the machine is told to boot from the drive, what file does it look for? What is the critical file on the drive that starts the whole deal?

    ~JK

    JK

    Bios instructs where to look for the files. MBR is on all drives from when they are formatted. Even USB drives. It looks for a bunch of files most notably ntldr. that is the file that kicks off the rest of the needed files. If you ever got the "bootmgr is mssing" thats it. it then "bootstraps" starts loading the drivers that let it communicate with the outside world via devices.


    Ken
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  4. Zidane24
    Posts : 5,807
    Windows 7 Home Premium x64 - Mac OS X 10.6.4 x64
       New #3

    Ken is correct...when you format any storage device a MBR gets written....

    Now lets look at the boot process...BIOS kicks in...Boot Menu->USB Device...at this moment the MBR kicks up and looks for any bootable code...it notices an active partition then it looks inside for any file that will start the boot process (files like Ken posted above)...it is then only a matter of booting those files and letting the code handle itself...
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  6. zigzag3143
    Posts : 28,845
    Win 8 Release candidate 8400
       New #4

    Better description Chris Thanks
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  7. Jonathan_King
    Posts : 13,354
    Windows 7 Professional x64
    Thread Starter
       New #5

    Why do the Windows 7 installation files need to be on an NTFS partition?

    I heard rumor somewhere that they don't, but no explanation/link was provided.

    What would I do if I wanted to have the files in a directory a little deeper down? Could I put a boot loader (e.g. GRUB) on the drive, and tell it to run ntldr? BTW where is ntldr? Why can't I find it, even when OS files are shown?
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  8. zigzag3143
    Posts : 28,845
    Win 8 Release candidate 8400
       New #6

    for anyone interested there is a better description of booting here NTLDR - Wikipedia, the free encyclopedia
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