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Is EFI booting something hardware specific? I have a desktop motherboard with a UEFI Bios, but I can only boot from USB drives in "UEFI" mode. Both the DVD drive and the HDD's (a RAID 0 array) boot only on legacy mode. Do the HDDs need to have a GPT partition table in order for them to boot in UEFI mode?

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2 Answers 2

up vote 7 down vote accepted

(U)EFI-based systems, by specification, can only boot from GPT-style disks. The traditional BIOS can boot from MBR-style disks, and in some cases (depends on the manufacturer), they can also boot from GPT. However, as per the UEFI specification, the disk should have a GPT partition table.

This MSDN article describes it well:

Systems that support UEFI require that boot partition must reside on a GPT disk. Other hard disks can be either MBR or GPT.

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Then how do I boot from a DVD in UEFI mode? –  joaocandre Mar 8 '13 at 22:27
    
@joaocandre the EFI shell itself is compatible with a typical bootable DVD. CD/DVDs do not use MBR/GPT style partition schemes, so they are not affected by this change. The EFI shell will look for the relevant firmware images on the disk, and then proceed to boot using the ones it found. –  Breakthrough Mar 8 '13 at 22:42
    
Problem is, when I set boot mode to "UEFI" only in BIOS, I cannot boot from the DVD drive. –  joaocandre Mar 8 '13 at 22:46
    
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As a practical matter, at least some EFIs can boot from MBR disks. Certainly some (but not all) of my EFI-based computers can boot from USB flash drives partitioned with MBR. I don't believe I've tested with hard disks, though. Despite its 2000-page length, there's a lot omitted from the EFI spec, and differences in the rules that specific EFIs use to determine boot mode (BIOS/legacy vs. EFI) have slipped into those cracks, which explains inconsistencies in whether specific DVDs or hard disks boot in BIOS/legacy vs. EFI mode. –  Rod Smith Mar 9 '13 at 23:13

UEFI does effect how OS's boot. You need to have space allocated for the UEFI on the harddrive. I believe with most Linux operating systems this is either done automatically or you must create a partition to host the UEFI.

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The UEFI itself is a firmware image uploaded to the motherboard itself, and has nothing to do with the actual disk. –  Breakthrough Mar 8 '13 at 22:24
    
Yet it does need a partition –  Griffin Mar 8 '13 at 22:25

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