If you're coming here from Google searching for how to convert a GPT disk layout to MS-DOS/MBR and don't want to read through my (probably boring) story, click here ;)
Adventures with Hybrid EFI
My gaming PC has been long overdue due for a reformat. I naively allocated only 30GB to the Windows partition (and the other 120GB to 3 flavours of Linux) thinking I wouldn't use Windows for much other than Starcraft 2, but a few months back I had the urge to play Battlefield 2 again. Ever since installing and fully patching it disk space has been running pretty tight. I had to disable sleep, hibernation as well as system restore and still only had 4GB of free space, so my filesystem became fragmented easily. With the release of Windows 8 Customer Preview (download it free here), I figured it was a good time to reformat my disk and reinstall all my OSs from scratch.
I figured while I'm at it, I would make all of the big changes at once and enabled EFI booting on my Gigabyte GA-Z68A-D3H board. Little did I know that when the BIOS says "EFI," it really means Gigabyte's "Hybrid EFI" implementation and not UEFI (although in retrospect, the fact that I made the change in the BIOS should have been enough of a hint, right?). With Hybrid EFI enabled, Windows 7 and Windows 8CP installed perfectly and even created a nice GPT disk layout so reinstalled my games and activated Windows 7. Then I rebooted to play around in Windows 8CP for a bit (I do not like it, btw).
I then tried installing Fedora 16. To my surprise EFI booting failed every time, despite the all of the Fedora 16 installation media being EFI-capable. When attempting to boot from my Fedora 16 Live (x86_64) USB key I just would get a black screen with "........." printed one dot a time and then it would proceed to fall back to the next boot device (Windows boot manager on the hard disk). Upon re-examining my BIOS settings, I was disappointed to find that the setting was actually called "CD/DVD EFI Boot Option" indicating that perhaps USB EFI booting was not supported. Fair enough, I burnt the same F16 image I was using on the USB key to a CD and tried again. The same "........." text appeared.
It was then as I went back to boot Windows 7 that I discovered my attempts to set it as the default OS from Windows 8CP removed my capability of booting Windows 7 somehow. At this point it was 2AM and I was fed up with this stupid Hybrid EFI. I looked for a way to revert to a good old MS-DOS/MBR partition layout. After some Googling I stumbled across Rod Smith's website. He has extensive documentation on EFI booting, including with Gigabyte's implementation of Hybrid EFI. He says that it shares a large amount of code with EFI DUET (tianocore) and although it does work natively with Windows 7, it is not a full UEFI implementation. That would explain the problems I was having with Fedora, then.
The actual GPT to MBR conversion
Through the Rod Smith's guidance and a few dirty tricks, I was successfully able to convert my GPT partition - without data loss or deleting any partitions - and then boot Windows 7 in legacy/MBR mode. In order to do this you'll need your Windows installation media at hand as well as a copy of the Fedora 16 Live media. If you don't have a copy of Fedora 16 Live handy, you can download the Live media ISO (64-bit) from a local mirror here. See the Fedora 16 Installation Guide for details on burning this image to a CD or on creating a bootable USB key.
Keep in mind that at this point I only had 3 partitions and a bunch of unpartitioned space on the disk, so conversion was a rather straightforward process (all GPT partitions mapped directly to primary partitions). Although it is theoretically possible to convert GPT partitions with >4 partitions by defining which ones are to be logical partitions after conversion, I have not tested this.
- Boot your Fedora 16 Live media and wait for your session to start. If you're having troubles booting, press Tab at the boot loader screen and try booting with the
- Depending on your graphics card, you'll either be presented with the new Gnome 3 Shell or with the traditional interface. Start a terminal session by putting your mouse in the top right corner of the screen and typing "terminal" in the search (Gnome Shell) or by selecting Applications > System Tools > Terminal (traditional interface)
- Install gdisk:
yum -y install gdisk
This may take a few moments.
- Make a backup of your current GPT scheme:
gdisk -b sda-preconvert.gpt /dev/sda
- Now we will attempt to convert your GPT disk layout to MS-DOS/MBR. Start gdisk:
You should be prompted with:
Command (? for help):
rto start recovery/transformation.
gto convert GPT to MBR.
pto preview the converted MBR partition table.
- Make any modification necessary to the partition layout. See Rod Smith's Converting to or from GPT page for more details on this.
- When you're happy with the MS-DOS/MBR layout, press
wto write changes to the disk.
- Shutdown Fedora 16 and boot from the Windows 7 installation media
- Enter your language & keyboard layout and then select the option to repair your computer in the bottom left corner.
- From the available options, select Startup Repair. Windows will ask for a reboot.
- Follow the previous three steps again to boot the Windows 7 installation and run startup repair
- Once again, boot the Windows 7 installation media but this time opt to open a command prompt instead of choosing startup repair. Type:
- Close the command prompt and run Startup Repair one last time.
That's it! You should now have a bootable installation of Windows 7 on a MBR partition layout.
- Rod Smith's Gigabyte's Hybrid EFI
- Rod Smith's Converting to or from GPT
- Rod Smith's Repairing GPT disks
- Microsoft KB927392: How to use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows