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Windows 7: GPT partition changes to MBR after installing 7 Ultimate x64

05 Feb 2013   #1

Windows 7 Ultimate x64
GPT partition changes to MBR after installing 7 Ultimate x64

Hello everyone

I tried installing 64-bit Windows 7 Ultimate on a 3TB Seagate SATA HDD. The list below shows the procedure I used:

1. Booted to the 7 Ultimate installation DVD
2. Launched Command Prompt, ran diskpart and clean and used the convert tool to successfully convert the only volume to GPT
3. Verified that the only disk in the list of disks was showing about 2.7 TB free space.
4. 64-bit Windows 7 Ultimate was successfully installed but on a 2TB partition. Looks like the partition is of MBR instead of GPT.
5. I booted to the installation DVD, launched Command Prompt, ran diskpart and clean. But this time no volume except for the DVD shows up in the list of volumes.

Please help me figure why the GPT partition which I created and verified was converted automatically to MBR after the successfully installation and how you can complete 7 on a 2.7 TB GPT partition without letting it be converted to MBR. Also, please advise me how to make the missing volume reappear in the Disk Part.

Thank you in advance,


My System SpecsSystem Spec
05 Feb 2013   #2

Microsoft Community Contributor Award Recipient


How to install Windows 64 bit on a uEFI/BIOS firmware:
UEFI (Unified Extensible Firmware Interface) - Install Windows 7 with

Boot the DVD in uEFI Mode.

GPT partition changes to MBR after installing 7 Ultimate x64-windows-8-downgrade-006-sb-posting.png

My System SpecsSystem Spec
05 Feb 2013   #3
Microsoft MVP


Are you sure you're installing in UEFI mode? Check the BIOS settings that CSM is set to UEFI or Dual mode and Legacy BIOS is disabled, then check the boot order shown above.

If you don't have a UEFI mobo then you'll need to install in MBR mode. You can partition using the Drive Options shown in steps 6/7 of Clean Install Windows 7 and don't need to wipe the HD.
My System SpecsSystem Spec

06 Feb 2013   #4

Microsoft Community Contributor Award Recipient


The Intel Desktop Board DZ77SL-50K has UEFI/BIOS firmware.
Intel® Desktop Boards featuring Intel Fast Boot Technology - YouTube
My System SpecsSystem Spec

 GPT partition changes to MBR after installing 7 Ultimate x64

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