Mark Partition as Active in 4 Ways [Step-by-Step Guide]?

The active partition holds the operating system's boot files, essential for starting up the computer. Upon system boot, the operating system within the active partition runs a process to assign drive letters to both primary and logical partitions.

In most instances, the active partition serves as the system partition for the operating system. Moreover, the "active" partition needs to be the boot partition, housing essential boot files such as BCD and BOOTMGR. In Windows systems, Partition C is typically the default active partition. It can also manifest as a separate System Reserve Partition.

This article from tools will guide you through the preparations, processes, and reasons for "marking a partition as active".

Tips Before You Mark Partition as Active

Before you begin, there are a few key points you should be aware of to ensure everything proceeds smoothly.

How to Mark a Partition as Active

Now that you're aware of the precautions, refer to the 4 methods below to set the partition as active.

1. Utilize the tool Partition Master

The simplest and safest method to achieve this is by using third-party software. For this purpose, we recommend tools Partition Master. It's a powerful tool that enables you to manage partitions in Windows 11/10/8/7. You can use it to set the partition as active for free.

Follow the guide below to set the partition as active.

Step 1. Run the partition manager software. On the disk map, right-click the target partition and choose "Advanced".

Step 2. Next, select "Set Active" from the dropdown menu. Click "Yes." Then choose "Execute 1 Task(s)" and click "Apply."

Aside from this function, you can also utilize Partition Master to resize a partition, clone a hard drive, migrate the Windows OS to another drive, convert the partition style of a disk, and more.

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2. Use Disk Management (only for 32-bit systems)

A built-in tool provided by Microsoft called Disk Management contains a suite of features for managing disks and partitions. Activating a partition is one such feature. Follow the steps below to learn how.

Step 1. Open Disk Management.

Step 2. Right-click the partition you wish to set as active, and then choose "Mark Partition as Active."

Occasionally, you might encounter the issue where the option "Mark Partition as Active" is grayed out. To resolve this, verify if the partition is logical or extended, as only primary partitions are allowed to be set as active in Windows. Another possible reason is that there's already an existing active partition that has been marked.

3. Use MSCONFIG

MSCONFIG (Microsoft System Configuration) is utilized to configure various settings. It can also be employed to activate a partition. However, MSCONFIG is unable to recognize partitions on different hard drives. Consequently, this method is only applicable to primary partitions on the same hard drive. Furthermore, it necessitates having Windows solely installed on the drive to activate another partition.

Step 1. Open the Start Menu. Type msconfig in the search box. Click on and run System Configuration.

Step 2. Navigate to the Boot tab. You will see a list of your current existing operating systems. The active partition has "Current OS; Default OS" indicated after its name.

Step 3. Select the other operating system and click "Set as default".

Step 4. Click "Apply" to confirm the changes, and then restart your computer.

4. Utilize Diskpart in Command Prompt

When you have multiple operating systems on the same drive, this method is often used to activate and make one partition bootable while marking another partition as inactive.

Step 1. Open the Start menu. Search for cmd and run the Command Prompt.

Step 2. Type in diskpart and press "Enter".

Step 3. Type in list disk and press "Enter".

Step 4. Type select disk 0 and press "Enter".

Step 5. Type list partition and press "Enter".

Step 6. Type select partition 3 and press "Enter".

Step 7. Lastly, type active and press "Enter" to set the partition as active.

("0" and "3" mentioned above are placeholders; replace them with the appropriate disk and partition number based on your specific situation.)

If you mistakenly mark the wrong partition as active, refer to the article below to find a solution.

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What to Do After Accidentally Marking Drive C as Active [2023 Update]

If your computer fails to boot after you unintentionally set drive C as active, and you're unsure how to activate the correct system partition, this article is here to help. Read more >>

Why Do You Need to Mark Partition as Active

An active partition is the one from which the computer boots. When the computer starts up, it looks for an active partition among the primary partitions. The boot sector initiates the boot loader, which knows the location of the operating system's boot files. Consequently, to ensure the correct operating system loads when the PC boots, you need to designate the partition as active in Windows.

If the partition that contains Windows boot files is not set as active, or if you incorrectly mark another partition as active, your computer will fail to boot and display an error message such as: Operating System not found or Missing operating system.

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Conclusion

This article presents 4 ways to set a partition as active in Windows 11/10. Among these methods, the tool Partition Master offers the simplest and quickest solution for managing this task. Furthermore, if you're searching for how to remove the active flag from a partition, you can refer to method 4 discussed above, as Diskpart also has the functionality to accomplish this.

Frequently Asked Questions (FAQs) on Mark Partition as Active

1. What does it mean to label a partition as active?

The active partition is the one from which the computer's BIOS or UEFI will boot the operating system. In other words, the active partition must contain the OS's boot files and bootloader.

2. Can I format an active partition?

You cannot format a disk or partition that is currently in use, including the Windows partition. The option to perform a quick format creates a new file table but does not fully overwrite or erase the drive.

3. How do I unmark an active partition?

Open the Start menu. Search for cmd and run the Command Prompt. Type diskpart and press "Enter". Type list disk and press "Enter". You will see the disk list. Type select disk 0 (replace "0" with the appropriate disk number) and press "Enter". Type list partition and press "Enter". Type select partition 1 (replace "1" with the appropriate partition number) and press "Enter". Finally, type inactive and press "Enter" to unmark the active partition.