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Dual-booting Windows 8 and Mountain Lion natively using EFI

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This is NOT about installing Windows 8 on a Mac, this is about using Apple’s EFI to boot Windows.

(If you don’t know what an EFI is, see Wikipedia)

Okay, so here’s what’s going on:

Apple has used EFI to boot OSX for years, but Windows has not supported this method of booting.

With Windows 8, Microsoft claims that you can boot with EFI so long as the drive you’re booting on has an efi partition and uses a GUID partition table.

Here’s the kicker, for years now, OSX has been using a Hybrid MBR partition table… that is they are using a GUID partition table with a matching MBR partition table embedded into it. This means that older versions of Windows can see the partition information from the older MBR system and will work properly using a legacy bootloader. But if you have an EFI installer for Windows, it will not let you install (or even BSOD!) if you try to use it as it sees the MBR and ignores the GUID.

A lot of posts online cite that Apple’s EFI implementation is based on EFI v1.1 and that Windows supports only EFI v2 and newer. This is NOT the case. It doesn’t work because the Windows installer sees the MBR in the hybrid partition table and decides that you are NOT using a GUID partition table even though you are.

Luckily, there is a way around this to get a fully native EFI-booted Windows 8 installation! But beware, this path (while awesome) is paved with daggers, so be prepared to pull your hair out in frustration.

Warning: These steps require you tocompletely ย erase your hard drive! Make sure you have all the materials and have backed up all of your data before proceeding.


  • A recent MacBook Pro (this will probably work on other Macs, but I don’t have any to test with) I’ve tested this on the 1st-gen Retina 15″ and a 13″ 2nd-gen i5 model.
  • A disk drive capable of reading DVDs (you’ll need an external drive for MacBook Retinas or MacBook Airs)
  • A Mountain Lion Install Disk or Netboot Installer
  • A CD/USB drive with the “Windows Support” files from Bootcamp
  • A Windows 8 Pro Install DVD


  1. Put the Windows 8 Disk in the disk drive
  2. Option-boot the computer and choose to boot off the “Windows” disk (Do not choose “EFI Boot” but make sure that it does show up, you’ll need to use it later)
  3. Once the installer gets to the setup screen, hit shift+f10. This will bring up a command prompt
  4. Type the following commands (this assumes that you only have one hard drive):
    1. diskpart (this puts you into the windows partitioning shell)
      1. select disk 0 (this selects the primary hard drive, make sure you don’t have any extra drives connected)
      2. clean (this erases your entire hard drive by removing all partition information)
      3. convert gpt (this converts your hard drive from an MBR partition table to a GUID partition table)
      4. create partition efi size=200 (this creates the efi partition where the bootloader will live)
      5. format fs=fat32 (this formats the EFI partition as fat32 so that Windows can write to it)
      6. create partition msr size=128 (this creates a “MicroSoft Reserved” partition… because microsoft)
      7. create partition primary (this uses the rest of your free space to create a usable partition)
      8. format fs=ntfs quick label=Windows (this formats the Windows partition and labels it as “Windows” which is what OS X will see)
      9. exit (this exits the windows partitioning shell)
    2. wpeutil reboot (this tells the computer to reboot)
  5. Option-boot the computer when it reboots, but this time choose “EFI Boot” instead of “Windows”
    1. Remember to press the any key to boot into the installer!
  6. Choose to use a Custom Install and install Windows 8 to “Partition 3” (The only primary partition)
    1. Make sure you leave the install disk in the drive through the whole install or you could get a BSOD
  7. Install the Windows Support software from your CD/USB drive to gain full functionality of your computer
    1. Congratulations! You now have a natively-EFI-booting Windows 8 Install! Now, on to dual-booting OSX…
  8. Open “Disk Management” in Windows.
    1. Find your “C Drive” partition and resize it by right-clicking on it and choosing “shrink volume”
      1. Shrink it by the size you’d like your OSX installation to be. ie. if you want to give OSX 100GB, use 102400MB
    2. Right-click on the now empty area at the end of the drive and make a new “Simple volume” Don’t format it.
  9. Reboot the computer into your OSX install disk/Netboot
  10. Open Disk Utility
    1. Choose “disk0s4” as this will be the 4th partition on disk 0
    2. On the “Erase” tab choose “Mac OS Extended (Journaled)” since this is what OSX likes to use.
    3. Give it a label that you like (Apple defaults to “Macintosh HD”)
    4. Hit Erase
    5. Exit Disk Utility
  11. Install OSX on your new partition.
  12. Congratulations! You are now dual-booting OSX and Windows in a 100% EFI environment! Happy computing ๐Ÿ™‚

Note 1: If you get a BSOD during install, make sure that you have NOT removed the Windows 8 install DVD from the disk drive… during install, removing the DVD at any time will produce a BSOD even though the OS no longer needs the disk to install.

Note 2: Windows now shows up in option-boot as “EFI Boot” instead of “Windows”

Note 3: Because we created the partition that OSX uses in windows, it no longer shows up in “My Computer” in Windows… Here’s how to fix that:

  1. Open “Disk Management”
    1. Right-click on the partition that you created for OSX (it should be labeled as an HFS partition)
    2. Choose “Change Drive Letter and Paths”
      1. Choose “Add”
        1. Assign it to a drive letter of your liking… I used “E”
        2. Hit OK
      2. Hit OK again
  2. You now have read-only access to your Mac Partition!

Update 1: I’ve been informed that for some models the sound does not work in Windows when booted via EFI. It appears to affect models that use the Cirrus audio controller. I’ve gotten ahold of a test unit and will see if there’s a workaround.

Update 2: Added formatting into step 4 to resolve possible BCD-related problems.

Update 3: Added “select disk 0” to step 4, you can’t do anything if you don’t specify the disk.

Written by David

January 18th, 2013 at 12:51 pm

Posted in EFI,OSX,Windows

Tagged with , , , , ,

123 Responses to 'Dual-booting Windows 8 and Mountain Lion natively using EFI'

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  1. Yes, in Ubuntu it’s /dev/sda for the first drive
    In OSX it’s /dev/disk0

    No need for refined if you followed that guide. Despite what’s said in the guide I’ve got OSX booting through grub, though it’s definitely non-standard ๐Ÿ™‚

    Mike D

    10 Feb 14 at 1:41 am

  2. An update for Mid 2010 MacBook Pro.
    They (mine at least) still have the problem of “cannot update boot configuration”. I just tried it with Windows 8.1 and ran into the same problem as before, so it doesn’t seem it’s possible on MBs that old.


    12 Feb 14 at 12:56 pm

  3. You could try resetting PRAM/NVRAM as others seem to have had success that way.

    Mike D

    12 Feb 14 at 11:16 pm

  4. Resetting did actually help and I finally managed to boot to Windows using EFI.
    However, once I was in Windows I was plagued with BSODs and random restarts, so I’m back on OSX.

    One thing I noticed during installation that might ease the steps of future, was that partitioning the harddrive was unneccessary.
    I booted straigt to “EFI Boot” and pressed Shift+F10 after selecting the language to start a command prompt.
    From there I started “diskpart” and ran only the following commands:

    select disk 0
    convert gpt

    After exiting diskpart and closing the command prompt I chose a custom installation of Windows (as opposed to the upgrade option). When it asked me which harddrive I wanted it installed on I chose the only one listed, then clicked the “New” button. This then created all the partitions needed.
    So it seems the guide can be simplified a bit.


    13 Feb 14 at 2:52 pm

  5. Glad to hear that the NVRAM reset helped.
    Did the BSOD’s mention an unhandled thread exception or something like that? Or maybe mention the igdkmd64.sys Intel graphics driver?

    Mike D

    13 Feb 14 at 3:10 pm

  6. Yeah, that was one of them.
    I fixed that by deleting the file in question.
    The other problems occured during installation of the Bootcamp-drivers. Some times during the nVidia installation, other times during some other driver. After a couple of those installation crashes/restarts something in Windows probably got corrupted as it refused to start any more.
    I don’t remember the BSODs after this mentioning any files, and it was a different message than the threading one. I want to say the error message included the word “system” but at that point I was pretty tired of the whole thing and had given up.


    13 Feb 14 at 3:15 pm

  7. Thanks for the update,
    The reason that the guide uses a “more complicated” method than you described is because you cannot boot the EFI windows installer on most models (something about the way the hard disk is formatted prevents the windows installer from booting). So the more complex method is described since it works in most cases.
    Also, by manually creating the partitions you have more control over where on the disk (and the size) of the various partitions (super useful if you’re trying to do something unusual).


    13 Feb 14 at 3:16 pm

  8. I have a dual graphics Mac as well and it does cause problems.
    Bootcamp somehow disables the Intel graphics chip but as we’re not using Bootcamp this does not happen.
    As a consequence of this both graphics chips are detected. The Intel driver can cause crashes or black screens on mine.
    Similarly the Nvidia driver causes the PnP screen to drop out, also resulting in a black screen.
    As a result of these issues I’ve disabled both the Intel and Nvidia chips in Device Manager. On rebooting the Microsoft Basic Display driver will load and the system is then usable.
    Obviously gaming wouldn’t be feasible (I wouldn’t imagine) but as I’m not a gamer it’s actually very usable for me.
    Maybe a fix will be found eventually ๐Ÿ™‚

    (As an aside, the brand new Bootcamp drivers issued today, have the same outcome too – so now fix yet.

    Mike D

    13 Feb 14 at 3:24 pm

  9. Has anyone managed to try this on a Haswell Macbook Pro?

    Thinking of getting a MacBook Pro 15″ top model but without the Nvidia (Iris only) but haven’t found any reports of EFI working.

    Mike S

    17 Feb 14 at 2:59 pm

  10. Some people have installed Windows in Bootcamp on Haswell Mac’s and it actually got installed as EFI. It seems that (at least) some of them don’t create a hybrid MBR when Bootcamp partitions the disk. All kinds of problems are reported during installation such as not being able to install to a GPT disk and, oddly, not being able to install to a MBR disk.
    You really need to know whether Bootcamp created the hybrid MBR after partitioning and before the system restarts. Gdisk can tell you.

    If a hybrid MBR is created you should install in CSM (bios) mode.
    If no hybrid MBR is created (remaining GPT only with a protective MBR) you should install in EFI.

    Obviously you could ignore Bootcamp altogether and install Windows in EFI manually, like most of us have done following this guide.

    Mike D

    17 Feb 14 at 11:36 pm

  11. Thanks Mike.

    I fully intend to do an EFI install but haven’t found many reports of success. This model without NVIDIA should solve some of the problem but I still haven’t found anything about sound drivers working/not working.

    I guess so few people are doing EFI installs that the knowledge pool is shallow.

    Mike S

    19 Feb 14 at 1:49 pm

  12. Mike S, those that have installed in EFI on Haswell’s (whether in Bootcamp or not) have not complained about having no sound, to my knowledge.
    My mid 2012 rMBP (with Nvidia) has no sound in EFI and as both the Intel and Nvidia graphics chips are detected the only answer I found was to disable both and just use the Microsoft Basic driver, which actually works very well. It boots in about 6 seconds too ๐Ÿ™‚
    But that’s no good if you’re installing Windows for gaming purposes.

    In your position I’d try with Bootcamp first but after the partitioning stage (but before rebooting) I’d run gdisk to confirm whether a hybrid MBR had been created. If not then EFI should be good (but on rebooting I’d also perform a NVRAM reset).

    Mike D

    19 Feb 14 at 1:55 pm

  13. Hi,
    An update.

    Got my rMBP without Nvidia (11,2) and followed your instructions to get Windows 8.1 installed. Upon boot (before bootcamp) only basic graphics display, no network and no sound. After bootcamp drivers 5.1.5640 everything works perfectly. Network started, sound, Intel HD5200 recognised. All good … except having to install 500MB+ of Windows updates ๐Ÿ˜‰


    13 Mar 14 at 10:13 pm

  14. Hey
    works good this tutorials

    only the sound don’t works after install bootcamp drivers.

    Is there a Solution?

    I have MacbookPro 2011 Late 13
    without extra grafikkard. when i install windows via Bootcamp all Works but with EFI native the Sound isn’t working
    The New update gives no New function on Sound Problem

    Solution ?


    21 Mar 14 at 5:14 am

  15. Hey David. Thanks for the awesome walkthrough.

    I’m seeing two issues that I can’t find addressed in your article or the comments. This is on a 13″ Haswell/rMBP

    1) I don’t get an EFI Boot option while option-starting. Only the Windows boot option appears. Tried clearing NVRAM – no change.

    2) If I proceed with the windows-boot option, I get the black screen with blinking cursor, followed by black screen with the win8 logo, I can see the activity light blinking on my USB Win Install drive, then I get a BSOD about the drive having been removed or inaccessible.


    11 Apr 14 at 2:29 am

  16. In my experience I have had limited success when installing (EFI) off of a USB drive… Have you tried a USB Optical drive for the install?
    Also (I haven’t verified this), I have heard that Bootcamp on newer models sometimes does an EFI install when following Apple’s instructions.


    11 Apr 14 at 2:42 am

  17. […] I followed this guide: Dual-booting Windows 8 and Mountain Lion natively using EFI at insideTheAsylum I did this on my late-2013 15" which I configured to have no Nvidia GPU. Everything works and the […]

  18. […] has a power switch easily accessible. I am running Windows 8.1 which I have installed UEFI using this guide. Originally when I received the Sonnet I found out that the PCI slots were only 8x length and so […]

  19. Hello, and thank you for this post. I’ve a slight different situation. I’m trying to install win8.1 onto a clean hard drive for a PC. A dual boot with linux.

    I’ve been having trouble, but your blog has gotten me farthest along, so maybe you could give me more help.

    regarding this point:
    Option-boot the computer when it reboots, but this time choose โ€œEFI Bootโ€ instead of โ€œWindowsโ€

    I think this is MAC specific instructions to reboot but to obtain a list of boot options (eg. disk drive, etc). I don’t have a list of boot options that are titled “EFI boot”. I have other options, none of which include the DVD drive with the installation disk.

    The only UEFI boot option is to boot from the very hard drive that has not yet received windows. So my motherboard appears to be recognizing the new hard drive correctly, but I don’t know how to move past this step, and any suggestions would be very much appreciated.

    For what it’s worth, the mother board I’m using is a gigabyte 990fxa-ud3 and it doesn’t have any options to disable ‘secure-boot’–apparently it’s already compliant or some damn thing.


    4 Jun 14 at 6:42 pm

  20. Great guide. Just to share my experience: Install went fine on a Macbook Pro Mid 2009 (2.53ghz). However, default sound drivers were installed and there was no sound despite the levels fluctuating in the mixer. I guess it had the same problem because of Cyrris audio.

    However, after installing the bootcamp drivers (which worked just fine on non-EFI installs), the restart went into repair mode and I couldn’t get it to boot normally. After 2 days of this nonsense I decided to give up. I’m reinstalling OSX and will just do a normal bootcamp Win 7 (assuming THAT even works.)

    Lucky for me, this system is an old one that my friend gave to me after upgrading, which I just wanted for playing around in OSX. However, from the looks of it, it’s the same bullcrap even on newer systems. Another reason to add to my list to avoid buying Apple products.


    30 Jun 14 at 10:41 am

  21. Hello

    The Option with EFI doesn’t show up for me? any suggestions?



    10 Sep 14 at 1:29 pm

  22. Hello,
    I have a Mac Mini Server mid 2011 with the Intel quad i7.I would like to Install Windows 7 64 on my second drive which is 1 TB (Recently added) and wish to boot with this method but how much do I half to do.

    SN: C07G34JPDJY7

    Keith D

    25 Mar 15 at 5:39 pm

  23. […] + Win8.1 [Vanne] . There it was a EFI installation of Win8.1 rather than a MBR installation. Eg: Dual-booting Windows 8 and Mountain Lion natively using EFI at insideTheAsylum Hello Nando I am getting error code 43 How can I fix this Reply With […]

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