The disk you specified is not MBR formatted please select an empty MBR disk to convert

Some users have mentioned that when they want to make a primary partition as active with the DiskPart, they received an error message saying "The selected disk is not a fixed MBR disk. The ACTIVE command can only be used on fixed MBR disk." They have no idea why this message appears and want to know if they could fix this problem.

If you are under the same situation, this article will provide you with what you need. You will know why you see this error message and how to solve it.

The Reason Why The Selected Disk is not A Fixed MBR Disk Arises

Several possibilities would cause this "The selected disk is not a fixed MBR disk" problem. We list the most common two reasons below.

• The partition is formatted as GPT.

The active command only works on BIOS/MBR system. When the partition is GPT and your computer is installing a system in UFEI mode, the computer would have trouble recognizing the active command. 

It can also lead to the error message if the computer is booting in a wrong way. You can solve the problem by fixing the boot manager.

If you are confused about what MBR and GPT are, you can refer to the article about MBR vs GPT to get more information.

How to Fix "The selected disk is not a fixed MBR disk"

Now you know the reasons that lead to the error message, you can fix this problem with the solutions introduced below.

Method 1. Convert GPT to MBR

Since the active command only works on a BIOS/MBR system, converting the partition from GPT to MBR could solve your problem. You can choose DiskPart Command Prompt and Computer Management on your computer to conduct the conversion. But both of the two methods will require you to delete volume first, which means these methods are involved in data deletion.  

So we recommend you to choose a third-party partition manager - EaseUS Partition Master to fix "The selected disk is not a fixed MBR disk" without data loss. This tool supports users in resizing partitions, converting partitions from MBR to GPT or vice versa, deleting partitions in Windows, etc.

Please download and launch the software on your computer and follow the steps below to convert GPT to MBR.

• Click "Disk Converter" on the left menu. Select "Convert GPT to MBR" and click "Next" to continue.
• Select the GPT disk that you want to convert and click "Convert".
• Wait for the process completes.

Method 2. Fix Boot Manager

This method needs your Windows installation drive. If you can find the installation drive or DVD, follow the steps below to fix the Boot Manager.

Step 1. Boot your computer from the installation drive.

Step 2. Choose "Repair your computer" from the welcome screen.

Step 3. Head to Troubleshoot > Command Prompt.

Step 4. Type the following command:

• bootrec
• FixMbr bootrec
• FixBoot bootrec
• ScanOs bootrec
• RebuildBcd.

And press "Enter" after each command.

Step 5. Wait until the operation is finished, remove the installation drive from your computer.

Step 6. Type exit and press the "Enter" button.

Now restart your computer to check if it can boot properly, and check if the selected disk is not a fixed MBR disk error message is still exists. 

The Bottom Line

This "The selected disk is not a fixed MBR disk" problem happens mainly because of the conflict of MBR and GPT partition on your computer. Once you have understood the difference between MBR and GPT, you will know how to solve this kind of problem. EaseUS Partition Master is your best choice to manage your partition. With this tool, you can clone, format, and merge partitions without data loss.

After a Windows 8.1 update, my computer booted into a black screen. So I boot it from a created bootable USB and from there I tried to repair the start. I read some guides and learn I need to make primary partition as active in Diskpart, but when I did that, I got the following error message: "The selected disk is not a fixed MBR disk. The active command can only be used on fixed MBR disks." Any advice? Thanks!

What causes this problem?

If the partition you wish to mark as active is located on a GPT (GUID partition table) disk, or we can say the disk partition is on a UEFI System partition, the error will occur. In other words, this “active” command only works for a BIOS/MBR-based system, not for UEFI/GPT-based system. Besides, if there is something wrong with the boot manager or you set the boot mode to UEFI, this error will appear, too.

How to fix "The selected disk is not a fixed MBR disk" issue?

According to the above possible causes for the "active command can only be used on fixed MBR disks" issue, you can try to convert GPT disk to MBR, change UEFI to BIOS, or repair the damaged boot manager to check whether the problem can be fixed or not.

Method 1. Convert GPT disk to MBR without data loss

Since a GPT disk is related to UEFI boot mode, and this boot method cannot recognize such a concept as an active partition, so converting it to MBR might solve this issue. Usually, you can run the diskpart tool to convert GPT disk to MBR. But you must delete all existing partitions on the GPT disk, otherwise the conversion will fail. Namely, you will lose system partition and need to reinstall Windows after the conversion. Complicated and time-consuming!

To make it easier and safer, you can turn to AOMEI Partition Assistant Professional. It can change the boot disk between MBR and GPT without deleting partitions existing on the disk, so data loss can be avoided. Moreover, it can help you create a bootable media and then convert the system disk to MBR in WinPE mode when your computer cannot boot into Windows successfully. Below is how to do it step by step.

Step 1. Insert an empty USB drive into a working Windows computer, install and run AOMEI Partition Assistant Professional on that computer. Click the "Make Bootable Media" on the left side and follow the wizard to finish creating a bootable USB stick.

Step 2. Plug the created bootable USB drive into the computer with boot failure, and boot comptuter it from the bootable media. When you log in, you will enter the main interface of AOMEI Partition Assistant Professional.

Step 3. Right-click the system disk and select "Convert to MBR Disk".

Step 4. Click "OK" confirm your operation.

Step 5. Click "Apply" to commit the operation.

Method 2. Disable UEFI and change to Legacy

Because GPT is closely related to UEFI boot mode, you can try to disable it and switch it to BIOS legacy.

Step 1. Turn on your computer and enter BIOS settings by pressing a specific key (F1, F2, Del, etc) when the system is about to start.

Step 2. Use the arrow key to access "Security" menu, select "Secure Boot Configuration" and press "Enter".

Step 3. In the “Secure Boot Configuration” menu, choose "Secure Boot" and modify the setting to "Disable".

Step 4. Now, navigate to "Boot" tab and select "Boot mode" option. And change its value to "Legacy".

Finally, navigate to the Exit section and choose "Exit Saving Changes".

When all are done, you can reboot your computer to check if "The selected disk is not a fixed MBR disk" is resolved. If not, go for the next method.

Method 3. Fix Boot Manager via CMD

To fix damaged boot manager, you need to run some commands in Command Prompt. For this task, you need to boot your computer from the Windows installation media. In the Windows Setup window, press Shift+F10 to open Command Prompt, and then execute the following commands:

▶bootrec /rebuildBcd

▶bootrec /fixmbr

▶bootrec /fixboot

If you don’t have Windows installation media, you can use AOMEI Partition Assistant Professional to create a bootable USB drive and enter WinPE environment (refer to the first method), and then directly rebuild damaged MBR via this software.

Step 1. Launch the AOMEI Partition Assistant Professional, right click the system disk and choose "Rebuild MBR".

Step 2. Choose a proper MBR type and click "OK".

Step 3. Click "Apply" and "Proceed" to commit the pending operation.

Conclusion

Hopefully, these 3 methods can help you tackle with "The selected disk is not a fixed MBR disk" error message in Windows 10/8/7. Besides rebuilding MBR and converting disk between MBR and GPT without losing data, AOMEI Parition Assistant Professional also supports transfering OS to SSD, allocating free space from one partition to another, extending NTFS system drive without reboot, etc.

How to convert MBR to GPT using command prompt?

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