How can I create Windows install media that boots & installs UEFI ONLY?

Discussion in 'Windows, Linux & Others on the Mac' started by iMattux, Feb 25, 2016.

  1. iMattux, Feb 25, 2016
    Last edited: Feb 27, 2016

    iMattux macrumors member

    Oct 6, 2015
    I'm trying to install Windows 8.1 in UEFI mode on my Mac Pro 4,1 flashed to 5,1 with 3.46GHz Intel W3690.

    As far as I can tell, Windows will only create media that boots the way the box that creates the media is booted. If the box booted via BIOS/CSM, the media it creates will (only) install Windows in BIOS/CSM mode. If the box booted via UEFI, the media it creates will install Windows in UEFI mode.

    All the instructions I've found around the web for creating UEFI install media involve selecting UEFI mode in a PC's BIOS screen and creating the install media. Of course, we don't have that option.


    The solution is to remove the bootmgr file from the root of the install USB. Note that the USB MUST be formatted as a single partition GPT disk in order to get a 4,1 or 5,1 Mac Pro to boot in UEFI mode. It may or may not work with other hardware that allows access to the EFI firmware, but if a Mac Pro finds an MBR, it boots in BIOS/CSM.

    Furthermore, at least on my particular Mac Pro (as mentioned, a 2009 4,1 flashed to 5,1) it did not work when I formatted the USB drive using Apple's Disk Utility OR Gdisk - Sorry, Rod Smith. You are a legend and you have taught me much, but I had to use Windows diskpart to format the USB drive.

    So, here is the exact step-by-step:

    From any windows environment (I was booted in BIOS/CSM on my Mac Pro) open a command line prompt and type:

    list disk
    sel disk *N* (where *N* is the number of your USB drive from the list)
    convert gpt
    format quick fs=fat32 label="NAME"(where NAME is whatever you want to call your USB. Use quotes if you want to use a space, i.e. label="Windows 10")
    Then, still in Windows, I mounted the ISO I'd downloaded from MS and simply dragged everything EXCEPT the bootmgr executable to the root of the USB drive. Note that I did copy bootmgr.efi, just not bootmgr.exe.

    Reboot holding alt/option, select the USB drive labeled "EFI Boot" and follow the instructions.

    Here's what I've done:

    I initially ran into the fairly well documented "select the CD rom type issue", but worked around that by following the instructions here and I successfully created a Windows 8.1 DVD using a PC, an ISO downloaded from Microsoft, oscdimg and ImgBurn.

    I installed Windows 8.1 and upgraded it to Windows 10. You'd think I'd be happy and move on, but I have to make things difficult. :p

    I formatted the target drive as a GPT drive according to these instructions, but when I try to install to it, the Windows installer (booted in BIOS/CSM) tells me that it can't install to a GPT formatted drive.

    I successfully hacked my Bootcamp Assistant Info.plist and have the option to create a USB drive to install Windows 7 or later using Bootcamp Assistant. BCA reports copying Windows files, downloads the Bootcamp files and then simply reports that the install could not be completed. o_O

    However, the USB drive appears to have all the necessary files to install Windows, just not the bootcamp files. I have bootcamp files from a separate download and they installed without issue to the BIOS/CSM version previously mentioned.

    No matter what method I use to create the USB - Bootcamp, Rufus on Windows or by manually building it Windows - the USB shows the now familiar blue windows for a few seconds, then goes to a big blue screen and tells me:

    Your PC needs to be repaired.

    An unexpected error occurred.

    Error Code: 0xc0000001

    Use your install media to repair your PC or contact your Sys Admin...

    My Mac Pro shuts down after 30 seconds or so.

  2. ActionableMango macrumors G3


    Sep 21, 2010
    Based on your experience, it would seem that the installation DVD is vastly easier than the USB stick.

    I just stuck the retail Windows 8.1 disc in, rebooted, held down ALT/OPTION during startup, and selected the optical disc icon with "EFI" in the name.
  3. iMattux thread starter macrumors member

    Oct 6, 2015
    LOL. If I had a retail Windows 8.1 DVD, I'd have done the same thing. I didn't know how much trouble I was going to have, so I just bought a license for $30, no media. On one hand, it would have been easier to buy/use a retail DVD for $110...

    On the other hand, now that I know how, it's very easy to create a USB installer that I know will ONLY install UEFI 64bit Windows. The second part is the real key. If anyone reading this thread wants to install Windows in UEFI mode, I've shared my experience and the (simple) solution. Maybe the next person who doesn't want to use Boot Camp to boot using BIOS emulation won't have to search and read and research for 2 days.

    Isn't that what we're here for, my friend? To share information and help each other find solutions other than "buy the retail DVD"? ;)

    And for the record, the DVD I burned from the ISO wouldn't boot my Mac Pro in EFI mode, even after I modified the ISO image as detailed on various sites.

  4. ActionableMango, Mar 17, 2016
    Last edited: Mar 17, 2016

    ActionableMango macrumors G3


    Sep 21, 2010
    Absolutely, you shared a lot of good information. I do not put down your method at all.

    I wanted to mention my experience too, as an alternative for anyone else wandering into this thread looking to do an EFI install.
  5. d5aqoëp macrumors 6502a


    Feb 9, 2016
    You can use Rufus which is windows based disk utility which allows you to format your usb drive to gpt and create UEFI based installer.

    Link here

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