Question Undersrtanding the UEFI BIOS -Gigabyte H81m-S

inwell

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Dec 3, 2011
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Hi, This is my very first installation on UEFI

I wish to install Windows 10 on my brand new SSD with UEFI and GPT. I have Windows x64 bootable iso already downloaded via media creation tool from MS.So now I have a bootable DVD/USB.

My Gigabyte MB H81M-S has UEFI bios(F2, latest available on Gigabyte site) and I found three combinations.

A. OTHER OS
With
UEFI and Legacy Boot, UEFI Only and Legacy Only, etc.
Here all the available boot devices are displayed in the boot sequence. (Legacy and UEFI Prefix)

B. Windows 8/ 8 WHQL
With
Added Option of CSM Support.
When Selected CSM Support as "Always" I get all the same options that I get in OPTION A (OTHER OS)
In addition, I get the Secure Boot menu. Can be turned on/off
Here all the available boot devices are displayed in the boot sequence. (Legacy and UEFI Prefix)

C. Windows 8/ 8 WHQL
With
CSM Support selected to "NEVER"
I get the Secure Boot Menu only. That can be turned on/off.
Here only UEFI Prefix Boot Devices are listed in the boot sequence.

Now, practically option A and B look identical. How are they different in their implementation except for the Secure Boot feature?

Secondly, if I wish to install a fresh Windows 10 on brand new SSD in UEFI and GPT mode, all three options should achieve what I wish i.e. Win10 in UEFI mode with GPT disk, right? (of course, I will have to boot from UEFI prefix device in option A and Option B)

So, if the above scene is true, why one even needs that OTHER OS(Option A) combination? coz same settings are available in Option B i.e. Windows 8 + CSM Support ALWAYS ON.
 
Start with A to install since that give you the most compatibility - once Windows is installed you can set it to C since you'll have a boot device for UEFI. Ignore references to Win8 as that was probably all that was available when the bios was written. Also A was needed when Windows 7 and XP were options

Booting just with UEFI some NVMe devices won't be recognized and "new" hard drives may not be detected (screwing up a fresh install)

If your drive detects fine then just continue in UEFI. You can enable Secure Boot once you've got Win10 installed
 
Last edited:

inwell

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Also A was needed when Windows 7 and XP were options
Win XP and Win 7 cannot be installed with Option B ? Just need to Enable CSM to Always and Disable Secure Boot.... just curious
You can enable Secure Boot once you've got Win10 installed
So BIOS settings of UEFI can be changed after Windows installation? Without any trouble for booting? No need for the exact same BIOS settings used at the time of installation of the OS ?
Regards
 

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