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However this allow me to do the following question: in which a way should be done the service "Eject Media" that corresponds to INT 13H, AH=46H ? It seems to me that this service is executed, for example, when i need to eject a usb stick.
no, it's not. It's not needed. Linux does not use it for example as far as I know, and has not for many years.
Can you confirm this ? and that is Coreboot is indipendent from the kernel of a linux OS (in particular the grub 2) ?
It always has been, be design. But if grub 2 uses any BIOS services then it will need seabios there.
2 - The last question. I don't understand very well the answer of Ron:
"to expand on patrick's comment, any sort of output in the boot stage of coreboot significantly slows boot time. This is not a problem on most firmware, but on coreboot it's a big issue. Even the addition of 100 milliseconds is a real detriment to boot time".
Why ?
I'm not sure what your "Why?" is about, can you be more specific?
ron