Understanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64

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  1. inwell's Avatar
    Posts : 92
    Win10 Pro
       #1

    Understanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64


    Hi, This is my very first installation on UEFI

    I wish to install Windows 10x64 using UEFI and GPT on my brand new SSD. 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 settings in 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

    Thank You
      My Computers

  2. CountMike's Avatar
    Posts : 18,350
    W10+Developer Insider + Linux
       #2

    CSM (only) is practically legacy mode, no UEFI.
    If you want to do clean W10 install on new and clean disk just set BIOS to UEFI Only and windows will partition it and install in UEFI mode. Best to have disk all empty and unformatted and only disk in the system, specially if there's an OS on them. You can ad other disk(s) after installing Windows.
      My Computers


  3. Posts : 38,358
    windows 10 professional version 1607 build 14393.969 64 bit
       #3

    As CountMike commented select UEFI native (without CSM) in the BIOS.
    Then boot to the Windows 10 iso and install Windows.
    The partition style should be GPT.

    Once the SSD drive is GPT you can maintain or modify the BIOS settings: either UEFI native (without CSM) or UEFI hybrid (with CSM)
      My Computer

  4. Matthew Wai's Avatar
    Posts : 5,053
    Windows 10 Home 20H2
       #4

    inwell said:
    My Gigabyte MB H81M-S has UEFI bios(F2, latest available on Gigabyte site) and I found three combinations.
    UEFI and GPT have been working fine on my GIGABYTE H81M-DS2, on which I have never changed the default combination: "Windows 8 FeaturesOther OS" and "Boot Mode SelectionUEFI and Legacy".

    I can't tell whether I have seen your combinations B and C in my BIOS version F2.
      My Computer

  5. inwell's Avatar
    Posts : 92
    Win10 Pro
    Thread Starter
       #5

    Matthew Wai said:
    UEFI and GPT have been working fine on my GIGABYTE H81M-DS2, on which I have never changed the default combination: "Windows 8 FeaturesOther OS" and "Boot Mode SelectionUEFI and Legacy".

    I can't tell whether I have seen your combinations B and C in my BIOS version F2.
    Hi Matthew, these are OPTION B and C. B is actually nothing but Option A + CSM (Enable or Disable) and Option C is CSM totally OFF that is PURE/Native UEFI.
    Understanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64-img_20200214_121152.jpgUnderstanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64-img_20200214_121245.jpgUnderstanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64-img_20200214_121415.jpg

    Now as @zbook and @CountMike suggest, to use PURE/Native UEFI mode (OPTION C) and you personally confirm that Win 10 is installed in UEFI and GPT using OPTION A,we can say that all the three combinations can achieve what we wish for- UEFI+GPT(if we are ok with NO secure boot). (Ofcourse we need to select the UEFI Prefix bootable media for OPTION A and B).
    So again can we say that OPTION A is actually useless, as whatever OPTION A can achieve is achieved using OPTION B too (with CSM always ON and Secure BOOT set to OFF) ?

    Best Wishes....
      My Computers

  6. Matthew Wai's Avatar
    Posts : 5,053
    Windows 10 Home 20H2
       #6

    You may press F12 to take screenshots of your BIOS settings as shown below:

    Understanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64-secure-boot-mode-does-not-exist.jpg

    Understanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64-default-2.jpg
      My Computer

  7. inwell's Avatar
    Posts : 92
    Win10 Pro
    Thread Starter
       #7

    What are these Lan Pxe...., Storage Boot Option Control, Other PCI..., and Network Stack options needed for?
    In my case where we will boot via bootable ISO DVD or USB ( Legacy mode or UEFI prefix mode) do we need to set those parameters to particualr values? Or just ignore whatever the values are set ..?

    - - - Updated - - -

    Matthew Wai said:
    You may press F12 to take screenshots of your BIOS settings as shown below:
    Thank You. Learning something new ..always
      My Computers

  8. Matthew Wai's Avatar
    Posts : 5,053
    Windows 10 Home 20H2
       #8

    inwell said:
    Or just ignore whatever the values are set ..?
    As I said before, I just use the default settings—leave them unchanged—unless/until I have got a problem.
      My Computer

  9. inwell's Avatar
    Posts : 92
    Win10 Pro
    Thread Starter
       #9

    Matthew Wai said:
    As I said before, I just use the default settings—leave them unchanged—unless/until I have got a problem.
    Little curious...
    In native/full UEFI mode ,attached DVd(without disk) drive not shown in boot device list ? Or my motherboard bios is having issues ?
      My Computers

  10. Matthew Wai's Avatar
    Posts : 5,053
    Windows 10 Home 20H2
       #10

    "P0: HL-DT-ST DVDRAM GH60N" is my DVD drive.
    "Generic STORAGE DEVICE 0903" is my card reader.
    Both were empty when the following photo was taken.
    Understanding the UEFI BIOS Gigabyte H81M-S for Windows 10 Pro x64-img_20200221_173459_800x1027.jpg
      My Computer


 
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