The UEFI is a recent development by Intel and Microsoft that supports what is called Secure Boot, which requires all the loaded firmware to be signed or it won't be loaded. This is a problem for Linux, since the keys required for signing must, under the current GPL, be made public. This, of course, defeats the purpose. There are several workarounds, including some being used by Red Hat, SuSE, and Ubuntu, which are being discussed by the Debian developers and will probably be included in an update at some future point. For now, the UEFI specification allows Secure Boot to be disabled, and that is the recommended way to install Debian so that it boots under UEFI. It is also possible to switch on the legacy mode in most UEFI implementations, which allows the old MBR method to work as well.
Under UEFI, boot code is placed in a subdirectory in a special partition. Generally, this will be a subdirectory of /EFI in the first partition on the disk (formatted with the FAT32 filesystem). Generally, the boot modules and configuration files are placed in the /EFI/grub directory in the UEFI partition. Itis not a good idea to replace the default EFI module (usually /EFI/Boot/bootx64. efi) by copying the grubx64. efi module over it, as some have recommended in the past. Debian installation generally takes care of including the GRUB loader as one of the options when booting, and if it isn't the default option, the boot settings menu should be used to set it as the default. It can also be used to add it as an option if the installation doesn't do this for you.
Getting into the UEFI boot settings menu usually involves holding down certain keys while booting the computer, very similar to the way the old BIOS menus were invoked. Itis different for each computer model.
