Hi markus, Am 13.06.22 um 19:06 schrieb Markus Koßmann:
On 13.06.22 15:54, Simon Becherer wrote:
i understand: in mbr there is a grub part somewhere in the first 2048 sectors who say -> load/boot/.... in gpt in the first 2048 sectors this is not the case.
Not exactly
When booting in legacy/CSM mode the BIOS loads the first 446 bytes from first sector of boot disk (= MBR, GPT provides a fake MBR) , checks if there is A5A5 magic number in the last bytes of MBR and then starts this as boot code. When grub is installed in MBR this code loads and starts the second stage of grub. Which is located on another position on the disk. With MBR partition scheme that code can be hidden in unused sectors of the disk. With GPT there are no unused sectors. So you will have to provide a BIOS boot partition for that code
"will have" -> must i? or is "/boot/grub2" also ok?
When booting in UEFI mode the UEFI starts an EFI program , which name/path is stored in UEFIs NVRAM from the ESP as bootloader. When grub is installed , this should be either shim.efi ( with secure boot) or the efi incarnation of grub.
Then there is the restriction that BIOS ( and CSM ) usually doesn't support NVME protocol but only SATA protocol.
So you can't boot a NVME disk with CSM unless the rare case that the nvme disk provides an BIOS extension PROM with NVME driver.
mh, not so rare, my (older) asrock "m4a87td" motherboards boot fine with csm and mbr at nvme and the new board is a msi (number not here, if interrested i could provide) did also boot with csm from nvme mbr
And there is the Windows only restriction that the Windows bootloader only supports either legacy boot with MBR partition scheme or UEFI boot with GPT scheme
ok, will never boot windows on my computers ;-) simoN -- www.becherer.de