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(multiboot.info)Header magic fields

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The magic fields of Multiboot header
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`magic'
     The field `magic' is the magic number identifying the header,
     which must be the hexadecimal value `0x1BADB002'.

`flags'
     The field `flags' specifies features that the OS image requests or
     requires of an boot loader. Bits 0-15 indicate requirements; if the
     boot loader sees any of these bits set but doesn't understand the
     flag or can't fulfill the requirements it indicates for some
     reason, it must notify the user and fail to load the OS image.
     Bits 16-31 indicate optional features; if any bits in this range
     are set but the boot loader doesn't understand them, it may simply
     ignore them and proceed as usual. Naturally, all as-yet-undefined
     bits in the `flags' word must be set to zero in OS images. This
     way, the `flags' fields serves for version control as well as
     simple feature selection.

     If bit 0 in the `flags' word is set, then all boot modules loaded
     along with the operating system must be aligned on page (4KB)
     boundaries. Some operating systems expect to be able to map the
     pages containing boot modules directly into a paged address space
     during startup, and thus need the boot modules to be page-aligned.

     If bit 1 in the `flags' word is set, then information on available
     memory via at least the `mem_*' fields of the Multiboot information
     structure (Note: Boot information format) must be included. If
     the boot loader is capable of passing a memory map (the `mmap_*'
     fields) and one exists, then it may be included as well.

     If bit 2 in the `flags' word is set, information about the video
     mode table (Note: Boot information format) must be available to
     the kernel.

     If bit 16 in the `flags' word is set, then the fields at offsets
     8-24 in the Multiboot header are valid, and the boot loader should
     use them instead of the fields in the actual executable header to
     calculate where to load the OS image. This information does not
     need to be provided if the kernel image is in ELF format, but it
     _must_ be provided if the images is in a.out format or in some
     other format. Compliant boot loaders must be able to load images
     that either are in ELF format or contain the load address
     information embedded in the Multiboot header; they may also
     directly support other executable formats, such as particular
     a.out variants, but are not required to.

`checksum'
     The field `checksum' is a 32-bit unsigned value which, when added
     to the other magic fields (i.e. `magic' and `flags'), must have a
     32-bit unsigned sum of zero.