How to convert Windows 8 from UEFI to BIOS

UEFI certainly is preferable over BIOS. However, when you run into problems with UEFI, you might want to convert your Windows 8 installation from UEFI to BIOS. I accidentally stumbled across a method and was surprised how easy it is.

Michael PietroforteMVP By Michael Pietroforte - Thu, August 8, 2013 - 6 comments google+ icon

Michael Pietroforte is the founder and editor of 4sysops. He is a Microsoft Most Valuable Professional (MVP) with more than 30 years of experience in system administration.

I bought a new SSD for my Ultrabook and had to restore my Windows 8 installation from an Acronis True Image backup. I created the backup of the UEFI-based Windows 8 installation and then selectively restored the Windows RE partition, the EFI system partition, and the Windows 8 partition. I was then quite surprised that Windows 8 booted up after the restore (True Image was set to automatic reboot) because the PC was configured to boot in BIOS mode. (Acronis True Image was running on a Windows To Go USB stick.)

Restore a UEFI installation as BIOS installation with True Image

Restore a UEFI installation as BIOS installation with True Image

I wasn’t very pleased because I knew that the PC wouldn’t boot up if I changed the configuration back to UEFI. What happened? Since I restored in partition mode, Acronis True Image initialized the new SSD with the MBR partitioning scheme and not with GPT. This was enough to convert my Windows 8 installation from UEFI to BIOS.

Unfortunately, it wasn’t so easy to get rid of the BIOS installation again because a restore in disk mode failed. In disk mode, True Image automatically detects that the backup was created from a GPT partition scheme. However, it appears True Image was no longer able to modify the SSD disk, even though I booted up from a USB stick. True Image then tried to boot up its own operating system, but this failed with the error message: Kernel panic – not syncing: VFS: unable to mount root fs on unknown-block(1,0).

Restore a GPT partition scheme with True Image

Restore a GPT partition scheme with True Image

I guess the reason was because True Image tried to copy its Linux-based OS to the SSD, which was somehow totally blocked. I wasn’t even able to delete the partitions on the SSD with the Windows 8 disk management tool on my Windows To Go installation.

The solution was to boot from True Image boot media and then initialize the disk with GPT (Tools -> Add new disk -> Initialization Options.) I could then selectively restore the partitions from my backup. Windows 8 booted up in UEFI mode without problems afterward.

Initialize disk with GPT partition scheme

Initialize disk with GPT partition scheme

Note that you can’t use this method to convert a BIOS installation to UEFI because the EFI partition would be missing in your backup. The procedure to convert BIOS to UEFI is rather complicated. Maybe it is faster to simply install Windows 8 again on a UEFI PC.

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6 Comments- Leave a Reply

  1. ron says:

    Is there a typo in the title? Shouldn’t it be “How to convert Windows 8 from UEFI to BIOS”, you already have a link to an article converting from BIOS to UEFI …

  2. Oops you are right. I corrected the title now. Thanks a lot for the hint!

  3. marc says:

    not only a typo in the title, also 2 lines lower the same mistake I think

  4. marc, thanks! I changed it now.

  5. Dualjob says:

    After more than 10 hours works, here are the step for convert UEFI to BIOS for Windows:

    1. Convert disk from GPT to MBR, Using EASEUS Partition Master or WinImage or StarWindConverter
    Don’t need the Hidden partition that contain EFI
    2. Fix Can not boot up
    a) Boot using Windows Installation Disc
    – Go to repair
    – Exit to Command Prompt
    b) Using Diskpart
    – LIST DISK
    – SELECT DISK (followed by the number of the disk . most likely 0)
    – LIST PARTITION
    – SELECT PARTITION (followed by your partition number. choose the partition that contain “\Windows”)
    – ACTIVE
    – EXIT
    c) Using BCDBOOT
    – BCDBOOT C:\Windows
    d) Using BOOTREC
    – BOOTREC /FIXMBR
    – BOOTREC /FIXBOOT
    – BOOTREC /REBUILDBCD
    – BOOTREC /SCANOS

  6. Dualjob, thanks a lot for this detailed instructions!

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