The active partition contains the operating system's boot files, which support the startup of the computer. When the system boots, the active partition's operating system will run a drive image to assign drive letters to primary and logical partitions.
In most cases, the active partition is the system partition of the OS. Furthermore, the "active" partition must be the boot partition. It must contain boot files like BCD and BOOTMGR. Partition C is the default active partition in Windows systems. This partition can also exist as a separate System Reserves partition.
This article from EaseUS will present you with the preparation, the methods, and the reasons for "mark partition as active".
Before you start, you should be aware of a few important points to make sure that everything goes well.
- The operating system should be installed in the proper location on the hard drive.
- The OS must have created a boot sector on the active partition.
- The OS's bootloader and files should be contained in the active partition, and the OS's physical hard drive location should be known.
- Only primary partitions can be set as active.
- Only one active partition can exist on each physical hard disk.
- Multiple active partitions are allowed to exist on each different physical hard disk. (Only the active partition on the first hard disk detected by your BIOS will boot your computer.)
Now that you have learned the things that you should pay attention to, refer to the 4 methods listed below to mark the partition as active.
1. Use EaseUS Partition Master
The easiest and safest way to do this is by using third-party software. Here, we recommend you with EaseUS Partition Master. It is a powerful tool that allows you to manage your 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 to active.
Step 1. Run EaseUS partition manager software. On the disk map, right-click the target partition and choose "Advanced".
Step 2. Then, select "Set Active" from the drop-down menu. Click "Yes". And choose "Execute 1 Task(s)" and click "Apply".
Besides this feature, you can also use EaseUS Partition Master to resize a partition, clone a hard drive, migrate Windows OS to another drive, convert the partition style of a disk, etc.
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2. Use Disk Management (only 32-bit)
A built-in tool provided by Microsoft called Disk Management contains a series of features for you to manage the disks and partitions. Marking a partition as active is one of them. Check the steps below to learn how.
Step 1. Open Disk Management.
Step 2. Right-click the partition that you want to set active, and then select "Mark Partition as Active".
Sometimes, you may find the option Mark Partition as Active greyed out. To fix this, you should check if the partition is logical or extended because only the primary partition is allowed to be set as active in Windows. Another reason is that there's another active partition that is already marked.
3. Use MSCONFIG
MSCONFIG (Microsoft System Configuration) is used to configure a variety of settings. It can be used to set the partition active as well. MSCONFIG can't identify partitions on other hard drives. Therefore, this method only works for primary partitions on the same hard drive. Additionally, it must only have Windows installed in order to activate the other partition.
Step 1. Open the Start Menu. Type msconfig in the search box. Click and run System Configuration.
Step 2. Navigate to the Boot tab. You will see a list of your current existing OSs. The active partition has "Current OS; Default OS" after the name.
Step 3. Choose the other OS and hit "Set as default".
Step 4. Click "Apply" to confirm the changes. Then, restart your computer.
4. Use Diskpart in Command Prompt
When you have multiple operating systems on the same drive, this approach is often employed to make one partition active and bootable while marking another partition inactive.
Step 1. Open the start menu. Search for cmd and run the Command Prompt.
Step 2. Type in diskpart and hit "Enter".
Step 3. Type in list disk and hit "Enter".
Step 4. Type select disk 0 and hit "Enter".
Step 5. Type list partition and hit "Enter".
Step 6. Type select partition 3 and hit "Enter".
Step 7. Finally, type active and hit "Enter" to mark the partition as active.
("0" and "3" mentioned above are examples; replace them with the appropriate disk and partition number according to your own situation.)
If you mark the wrong partition as active, check this article below to find out the solution.
What Should I Do After Accidentally Marked Drive C Active [2023 New]
If your PC cannot boot after your accidentally marked drive c active, and you are wondering what to do to mark the correct system partition active, this article is for you. Read more >>
An active partition is the one from which the computer boots. When the computer boots up, it searches the primary partitions for an active partition. The boot sector will start the boot loader, which is aware of where the operating system's boot files are located. Therefore, to load the correct operating system when the PC boots, you must mark the partition as active in Windows.
If the partition that keeps Windows boot files is not active, or if you mark the incorrect partition as active, your computer will not boot successfully and will display an error message like: Operating System not found or Missing operating system.
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This post offers you 4 methods to set the partition as active in Windows 11/10. Among all the methods, EaseUS Partition Master provides you with the easiest and fastest one to manage the job. In addition, if you are looking for a way to remove the active flag from the partition, you can refer to method 4 mentioned above since Diskpart also has the ability to do so.
1. What does it mean to mark 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 include the OS's boot files and bootloader.
2. Can I format an active partition?
You can't format a disk or partition that is presently in use, including the Windows partition. The option to perform a quick format creates a new file table but does not completely overwrite or wipe 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 hit "Enter".
- Type list disk and hit "Enter". You will see the disk list.
- Type select disk 0 (replace "0" with the appropriate disk number.) and hit "Enter".
- Type list partition and hit "Enter".
- Type select partition 1 (replace "1" with the appropriate partition number.) and hit "Enter".
- Finally, type inactive and hit "Enter" to unmark the active partition.
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About the Author
Tracy became a member of the EaseUS content team in 2013. Being a technical writer for over 10 years, she is enthusiastic about sharing tips to assist readers in resolving complex issues in disk management, file transfer, PC & Mac performance optimization, etc., like an expert.
I love that the changes you make with EaseUS Partition Master Free aren't immediately applied to the disks. It makes it way easier to play out what will happen after you've made all the changes. I also think the overall look and feel of EaseUS Partition Master Free makes whatever you're doing with your computer's partitions easy. Read More
Partition Master Free can Resize, Move, Merge, Migrate, and Copy disks or partitions; convert to local, change label, defragment, check and explore partition; and much more. A premium upgrade adds free tech support and the ability to resize dynamic volumes. Read More
It won't hot image your drives or align them, but since it's coupled with a partition manager, it allows you do perform many tasks at once, instead of just cloning drives. You can move partitions around, resize them, defragment, and more, along with the other tools you'd expect from a cloning tool. Read More