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El-Torito: Difference between revisions
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New section "El Torito Structure"
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(New section "El Torito Structure") |
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boot image. Details about the options for ISO 9660 image production
can be found on the [[Mkisofs]] page.
== El Torito Structure ==
El Torito booting begins by the Boot Record of the ISO 9660
filesystem at block address 0x11. See also article [[ISO 9660]].
This Boot Record points to a Boot Catalog which is stored
in one or more blocks inside the ISO 9660 filesystem.
The content of Boot Record and Boot Catalog is created during
filesystem production by the ISO 9660 producing software.
The Boot Catalog lists the available boot images which may be
prepared for multiple system architectures, called "platforms".
These images are marked either as emulated floppies, or as
emulated hard disks, or as no-emulation images.
In any case they are the first stage in the boot process
where custom code from the ISO filesystem can be executed.
While the emulated boot images are to be interpreted
by the firmware as is supposed for floppies and hard disks,
the no-emulation boot images are on their own:
PC-[[BIOS]] reads from the Boot Catalog the number of
blocks to load, loads them (usually to segment 07c0) and then
executes them as code. As with a normal floppy or hard disk,
the DL register contains the BIOS drive number.
[[EFI]] interprets the boot image as [[FAT]] filesystem and
looks up a standardized file path for further processing.
The original El Torito specification mentions platforms
"80x86", "PowerPC", and "Mac".
Boot setups based on GRUB2 and ISOLINUX use "80x86" for PC-BIOS,
and a platform id 0xef for (U)EFI which is not listed in the
old specs.
== No-Emulation Mode ==
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