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Originally Posted by theNbomr The answer to this is quite architecture-specific. For PC-type architectures, Inside the Linux boot process gives a pretty good explanation of the state of affairs and ...
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  1. #11
    Linux Enthusiast Bemk's Avatar
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    Quote Originally Posted by theNbomr View Post
    The answer to this is quite architecture-specific. For PC-type architectures, Inside the Linux boot process gives a pretty good explanation of the state of affairs and the process that takes place as a kernel is launched by a bootloader.
    --- rod.
    Ok, that one I've read already, and my questions was intended a little more specific. I'll redefine it:

    In what mode is the CPU when it loads the kernel, is it real mode or does it go into protected mode, are there any entries made into the IDT by GRUB, which the kernel may use, or is it not defined by grub?
    Also at what address is the kernel loaded, and what's the maximal image size that GRUB can load?

    It's not answered in the IBM docs, and even though they give an idea of how it works, it doesn't go into detail.

    I know this is not something typically asked in the newbie section, but I thought, now we're talking GRUB anyway ...

    Anyway, if you don't know the answer, I don't mind, but I've had a hard time finding the answers, and I still haven't got them.
    Last edited by Bemk; 07-27-2010 at 09:29 PM.

  2. #12
    Linux Newbie theNbomr's Avatar
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    I presume by the fact that a kernel can be larger than 1 MB, that an X86 CPU must be in protected mode. Real-mode addresses are only 20 bits wide (1 MB). The rest I don't know.

    --- rod.
    Stuff happens. Then stays happened.

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    Linux Enthusiast Bemk's Avatar
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    Quote Originally Posted by theNbomr View Post
    I presume by the fact that a kernel can be larger than 1 MB, that an X86 CPU must be in protected mode. Real-mode addresses are only 20 bits wide (1 MB). The rest I don't know.

    --- rod.
    I think I'll keep on searching. It's kind of funny though that it is so hard to find documentation.

    The system doesn't need to be in PM to access addresses from 0x100000 and up. All you need to do is enable line A20, and it will allow you to use the 32 bits addressing mode, instead of the 20 bits accessible in real mode.

    I'm (once again) not sure about this however.

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    Linux Newbie theNbomr's Avatar
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    Gustavo Duarte, The Kernel Boot Process seems to fill in some of the blanks. I think the best documentation to be found on this subject will be written in C and assembler.

    --- rod.
    Stuff happens. Then stays happened.

  5. #15
    Linux Enthusiast Bemk's Avatar
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    Quote Originally Posted by theNbomr View Post
    Gustavo Duarte, The Kernel Boot Process seems to fill in some of the blanks. I think the best documentation to be found on this subject will be written in C and assembler.

    --- rod.
    Thanks, this one contained a link to the Multiboot standard, which defines the system state and everything.

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    Quote Originally Posted by flipjargendy View Post
    Just curious... I am installing Debian Squeeze, right now. Do I really need to install grub (or any boot loader) since I am only installing one OS.

    Seems like I shouldn't have to. BIOS takes care of that if there is one OS... right?
    This question sounds like you came from the Windows environment. What happens is in Windows they install their own bootloader (if you install Windows first, lilo or grub will be destroyed). So yea lilo or grub are needed.

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