Re: linux bootup

From: Kasper Dupont (kasperd_at_daimi.au.dk)
Date: 12/07/04

  • Next message: Dr. Nikolaus Schaller: "Crashing dlopen() on Sharp Zaurus C860" 
    Date: Tue, 07 Dec 2004 14:12:29 +0100

    Uday Mullangi wrote:
    >
    > Hi,
    > Could anyone answer few questions on bootup sequence of linux that i have.
    >
    > 1.What is the typical size of a bootloader?

    There is no such thing as a typical size, it vary a lot.
    AFAIR syslinux is about 5KB. Grub is a litle more than
    100KB.

    > Since the booloader code starts
    > from 0x7c00 and can touch till 0x9A000,

    I'm not sure what you think about here. The boot record
    on a PC is loaded on 0x7c00 and is 512 bytes long. (At
    least as long as you are booting from floppy or harddisk).

    > Can i assume that the max size of
    > the bootloader could be 0x9a000-0x7c00=0x92400[ 585kb ].

    Who knows? Because of crappy hardware design, it is nice
    to keep the loader within that limit. How much would you
    want to put in a loader? When the Linux development was
    started you would have been considered insane if you
    wanted to use 100KB for your loader. Today people really
    like grub in spite of that size, and personally I think
    it have almost every feature I could ever want in a loader.

    > What if the
    > bootloader exceeds this size?

    If you want a loader larger than that, you will have to do
    something else. And if the loader try to use some memory
    that just isn't there, it will not work.

    >
    > 2.Will the bootloader use the magic number of the(0xAA55) of the kernel
    > header? If so, when?

    Dunno. I believe that magic number originally existed
    because the first sector of a kernel image was in fact a
    loader (a primitve one).

    >
    > 3. Is the BIOS setting the IVT for loading linux standardised? (I asked the
    > because some vector numbers are used by the bootloader BIOS calls). If so,
    > where can i get the details?

    The loader will need to use some of these to access disk,
    keyboard, serial port, and screen. (Not all loaders need
    all of them). But Linux itself does not need them (except
    from stuff like VESA and ACPI). 

    -- 
Kasper Dupont
  • Next message: Dr. Nikolaus Schaller: "Crashing dlopen() on Sharp Zaurus C860"

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