Converting Windows 8 BIOS installation to UEFI:

Prerequisites:

  1. Start the computer in BIOS-mode (not UEFI!)
  2. Take a full and working backup of your machine.
  3. You will need at least 300MB of space to create a System (EFI) partition on your root disk, This partition is not required to be at the start of the disk It can be at the end.
  4. Microsoft wants the EFI partition to be 300MB, it can be kind of subjective on a good size, but its not just the Windows boot loader (a few MB) that sits there, BIOS updates (including automatically from Windows Update), Linux boot loaders like GRUB2 and maybe even the Linux kernel in some cases, as well as UEFI tools like memtest and opencore do sit there.
  5. HAVE A FULL DISK BACKUP OF YOU'RE ROOT DRIVE! It is easy to fail during this process and any mistake can render Windows 8 permanently unbootable! As well as major data loss.
  6. Download gptgen 1.1 To your Windows 8 Downloads Folder.
  7. Optional: Do not have any other drive plugged in to reduce risk of formatting wrong drives.

Let’s get started!

  1. Boot into your Windows 8 or Windows 8.1 machine, and login as administrator
  2. Right-Click Start button in corner and select Disk Management (Posable on both 8.1 & 8.0, for 8.0 its just a brief pop up windows instead of a button).
  3. Shrink the Windows 8 NTFS partition by 300MB and then create a partition at the end of you're disk that is 300MB in size. Can put any Windows recognized file system in that partition.
  4. Run “Command Prompt”as Administrator.
  5. Run gptgen.exe -w \\.\physicaldrive0 in an elevated (admin) command prompt. After running this your computer will not boot in BIOS mode any more. DO NOT REBOOT OR SHUTDOWN THE COMPUTER UNTIL THIS GUIDE IS DONE!
  6. Run diskpart.
  7. List all your disks with list disk.
  8. Select the disk you want to convert from BIOS to UEFI with select disk 0 (replace 0 with you're wanted disk).
  9. List all partitions on the disk with list part.
  10. Select the 300 MB partition with select part 1 (Replace 1 with the 300MB portion).
  11. Create the EFI partitions with create part EFI size=100 offset=1.
  12. Format the EFI partition to FAT32 with format fs=fat32 label=”System” quick.
  13. Assign drive letter S to System/EFI partition with assign letter=S.
  14. Now we need to copy the UEFI files from the Windows installation to the EFI-partition.
  15. Exit diskpart with by typing exit.
  16. Run the command bcdboot C:\Windows /s S: /f UEFI.
  17. Restart your computer again, go into BIOS/UEFI and enable UEFI (Or VM settings in VMware), and enjoy!
Source | Source Date: March 5th, 2015 | Repost Date: May 16th 2025



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