Technical Notes about fixes, procedures and references for Windows (generally focused on Windows 8.1)

This is for the more technically inclined and works as a reference for me, I try to record the procedures, fixes, etc. that I have used here. As sometimes websites disappear or change or are removed over time, I record an abridgment of the procedures and link back to the site for the original source.

These are technical procedures and can very likely render your computer entirely non-working (not even able to boot). Please DO NOT follow these unless you are experimenting in a controlled environment or know what you are doing.

Converting Windows BIOS installation to


Convert a 8 BIOS (MBR) installation to UEFI (GPT) without moving, copying or losing data.


  1. Create a system repair disc ( ). You can skip this step if you have a Windows installation media. Is a good measure to reboot and verify you can start your system from this disc.
  2. Identify which disk you want to convert (usually is #0). This can be done by looking at the number in the Windows Disk Management.
  3. Download gptgen from here . (You could use the Windows Disk Management Tool for this too. (diskmgmt.msc)) This tool will allow you to convert your MBR disc to GPT with the data included.
  4. ATTENTION: After this step, your computer CANNOT BOOT until the whole process is completed. DO NOT Shut Down Unless Instructed to!
    1. Unzip gptgen and then run CMD with elevated privileges. (replace the 0 with the identified disk number).
    2. This *will* result in a BSOD shortly after and it's to be expected:
    3. gptgen.exe -w \\.\physicaldrive0
  5. Boot using your Windows installation or previously generated system repair disc.
  6. Choose language and preferences, and then select Repair Your Computer -> Troubleshoot -> Advanced options -> Command Prompt
  7. We will need the disk partitioning tool. With this, we will recreate the boot partitions. Type:
    1. diskpart
  8. Identify the boot disk where Windows is located, typing:
    1. list disk
    • Something like this should appear:
    • Disk ### Status Size Free Dyn Gpt
    • -------- ------------- ------- ------- --- ---
    • * Disk 0 Online 128 GB 0 B *
  9. Once identified, select the disk (replace with the correct number):
    1. select disk 0
  10. Verify the partitions:
    1. list partition
  11. Something similar at the info below should appear.
    • Partition ### Type Size Offset
    • ------------- ---------------- ------- -------
    • Partition 1 Primary 350 MB 1024 KB
    • Partition 2 Primary 126 GB 350 MB
  12. Delete the previous system partition:
    1. select partition 1
    2. delete partition
  13. Create the new boot partition, Microsoft reserved partition:
    1. create partition EFI size=100 offset=1
    2. format quick fs=fat32 label="System"
    3. assign letter=S
    4. create partition msr size=128 offset=103424
  14. If you list the partitions again, you should have ended up with something like this:
    • Partition ### Type Size Offset
    • ------------- ---------------- ------- -------
    • Partition 1 System 100 MB 1024 KB
    • Partition 2 Reserved 128 MB 101 MB
    • Partition 3 Primary 126 GB 229 MB
  15. Ensure that your Windows installation is mounted, replacing 3 with the volume number of the Windows installation (usually 1):
    1. list volume
    2. select volume 3
    3. assign letter=C
  16. Exit diskpart:
    1. exit
  17. Generate boot partition data, replacing C: with the letter of the Windows installation (usually C:):
    1. bcdboot c:\windows /s s: /f UEFI
  18. All finished restart your computer!