Hi Thomas
many thanks for you clear description.
I didn't manage to build a MBR from a fresh formatted SDCard under Linux.
The partition start was always to high.
But I guess this is off topic here (?)..
Have a sunny day
Daniel
Am Dienstag, 3. Dezember 2019 schrieb Thomas Schmitt:
> Hi,
>
> > that is what Thomas meant with hybrid ISO having both, good old MBR
> > BIOS and EFI support.
>
> That's modern extra hybrid: {PC-BIOS, EFI} x {DVD, USB-stick}
> The older ISO hybrid concept is {PC-BIOS} x {DVD, USB-stick}
>
> For the old hybrid, T2 uses a GRUB x86 El Torito Image and a GRUB MBR which
> is specialized on executing the El Torito Image as x86 program.
> This boot equipment can be seen in
> t2-minimal-glibc-gcc-i586-r48710.iso
> The El Torito image is accessible in the ISO as
> /boot/grub/i386-pc/eltorito.img
>
> The newer extra hybrids additionally have an EFI System Partition image as
> file (Fedora, Debian amd64, ...) or as nameless appended data blob (Knoppix
> 8.2+).
> This image is a FAT filesystem with the UEFI prescribed start programs
> and some GRUB menu (Knoppix uses SYSLINUX which does not work from DVD).
> The image gets advertised in the ISO as El Torito image for EFI and as
> partition of MBR type EF or of GPT Type GUID
> C12A7328-F81F-11D2-BA4B-00A0C93EC93B.
>
> As said, UEFI prescribes these partition IDs for hard-disk-like devices and
> El Torito for optical media. Many EFI implementations look at more places
> for the /EFI/BOOT/BOOT*.EFI programs. Microsoft Inc. obviously expects that
> all FAT filesystems get inspected which have a Microsoft MBR partition type
> for data. E.g. 0C or 0E. There are howtos which rely on this. No firmware
> implementer will dare to insist in a narrow interpretattion of UEFI specs.
>
> The fact that an inofficial location of the EFI programs works on one
> firmware does not indicate that it would work on the next firmware.
> So it is better to obey the specs veven if they are fewly enforced.
>
>
> Have a nice day :)
>
> Thomas
>
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