HDD in UEFI (gpt) in OS but Legacy in BIOS?

[jonomaia]

I was reading about Legacy and Uefi and the correct/best bios settings for modern specs and realized that in my rig, the Bios options was in "legacy" mode ("Storage Boot option control" in a Gigabyte Mobo). Then i've booted in my OS and through disk management properties i found that both my HDDs are in "GUID partition table (GPT)" in "partition style settings".

Does that mean i could change it in BIOS without any risks? or there are any possibilies of data loss or system bugs?

PS: my HDDs are WD blue 2012 1Tb (primary partition) and an old seagate green 1.5Tb (as secondary)
Mobo: gigabyte 970a UD3P
Bios version: FB 06/01/2015

 

[HankB]

The EFI boot loader will look for a special /boot partition to find the files needed to boot. (That's where it is on Linux. I'm not sure where it is on Windows and it may be hidden.) You can look in disk manager (<windows>X -> Disk Management) to check if it is there. If it is not there and you switch to EFI boot your PC will not boot until you switch back. No harm will be done.

EFI requires GPT partitioning and cannot be configured for MBR partitioning.

If you switch partition types (GPT vs. MBR) all existing data will become unavailable. There are ways to recover some of it, but I wouldn't do that unless you plan to lose all existing data.

With Linux you choose EFI or Legacy boot when you install. In fact, to install EFI the install media has to boot EFI. I'm not sure of the requirements for Windows.

A PC with GPT partitioning can boot legacy and/or EFI without modifications. My laptop dual boots Windows 10 and Linux. The GRUB bootloader lets me select among several Linux distros and I can hit <F12> during POST to get the option to select Windows Boot Manager or (???) the other. Linux boots Legacy and Windows uses EFI.

The only option not available to me is Secure Boot because the Linux distro I usually use (Debian) does not support it.

Does this answer your question or did I do a poor job of trying to explain it? And FWIW I could be wrong in which case someone will hopefully correct me.

 

[jonomaia]

Thanks brother. i'm still a little confused but i think i've starting to understand.
focusing on windows and my specific case, in disk management, it shows both my drives as GPT. but in BIOS, it is setted to Legacy. If i could just switch IN BIOS and test to see if it boots (without the risk of loosing data, as you said from what i understood) i was willing to do. but, if the conversion is needed, i will just leave as it is.

 

[trents]

I know that you can have the bios configured for UEFI and still have the disk partition scheme be MBR. I recently encountered that scenario on my own rig. It ran fine but nonetheless converted the disk from MRB to UEFI with partition manager software. Apparently, your scenario shows us that you can have the bios in legacy mode but use disks with GPT and not experience issues. There might be a small performance hit if the bios is in legacy mode but otherwise . . .

You could try switching to UEFI in bios and see if it still boots. If it doesn't, just clear the CMOS.

 

[petteyg359]

The EFI boot loader will look for a special /boot partition to find the files needed to boot. (That's where it is on Linux. I'm not sure where it is on Windows and it may be hidden.)

No. Those are entirely separate things. EFI has no idea about your operating system, whether it uses mount points or drive letters, etc. EFI looks for an ESP (EFI System Partition), which could technically be used as /boot in Linux, but that is most definitely not the default configuration of anything. The ESP actually contains the bootloader executables, whether GRUB or bootmgr or whatever Apple uses these days or some other operating system or an EFI stub kernel for Linux that runs without a bootloader. For all but the last case, the bootloader is what looks up the actual OS (e.g. in /boot on Linux) and runs it.

@op, why do you think you need to change it? There's absolutely no performance effect.