On Mon 14 May 2018 at 23:29:43 (+0200), Pascal Hambourg wrote: > Le 14/05/2018 à 02:02, David Wright a écrit : > >On Sun 13 May 2018 at 19:08:48 (+0200), Pascal Hambourg wrote: > >> > >>Most of my early experience with UEFI boot comes from a rather old > >>Intel motherboard. Beside crippled UEFI support (no UEFI boot from > >>USB or SATA in AHCI mode), it had a couple of annoying requirements : > >>- boot in legacy mode only if the MBR contains a partition entry > >>with the boot flag set, regardless of whether the disk has a MSDOS > >>or GPT partition table. This behaviour is beyond any common BIOS > >>standard, but I have observed it on many other systems, mostly Dell > >>and HP ; > > > >In the case of GPT, I assume the partition entry with the boot flag set > >is the protective MBR. > > Yes, as the protective GPT partition entry is the only non-empty entry. > > >>- boot in EFI mode from GPT only if the protective partition entry > >>in the MBR has the boot flag unset. I admit this requirement is part > >>of the GPT specification, but really do not see the point in > >>enforcing such a minor detail. > >> > >>Anyway, these two requirements put together make it impossible to > >>boot in both legacy and EFI mode from the same GPT disk with this > >>motherboard. However they allow to boot in both modes from the same > >>MSDOS disk. But who still wants to use MSDOS format nowadays ? > > > >Is it impossible, then, to change the boot flag in a protective MBR? > > Of cours not, but it is even less convenient than switching the boot > mode in the firmware setup : boot the system, switch the boot flag, > reboot the system...
Sorry, I thought impossible meant not possible. I agree that booting up a system (that happens to be set to the wrong state) just to change the boot flag and then reboot is a lot less convenient than the process I use (which always lets you boot into the correct system first time, and only requires action when you want to change over). But the fact that you've experienced a crippled mobo does not IMHO mean that some of the scenarios you could use on less crippled systems shouldn't be discussed—nay, be treated as near impossible—in a web page that's meant to be throwing light on the matter. As written, the author just pours special magic sauce around, whatever that is. Cheers, David.