By Cherry / Last Updated June 27, 2021

Windows cannot format C drive in Windows 10

To format C drive means to format the system partition, or the primary partition that Windows or your other operating system is installed on. In some special situations, you need to reinstall operating system, and formatting C drive is an ideal way to clean system partition for reinstalling system while keeping data on other partitions safe.

However, formatting C drive is different from formatting other partitions in Windows: when you open "Windows Disk Management", right click C drive to format it, you can see the “Format...” is grayed out. While when you try to use Diskpart format partition, you will receive a message that “system partition is not allowed to be formatted”.

Format Not Allowed On Boot Volume

Why? To format C drive Windows 10 will delete everything on the Windows 10 system partition including system installed files, and your computer will be unbootable. Thus, Windows cannot format system partition in the disk Windows 10 while Windows running. So, how can you format C drive in Windows 10?

Format C drive Windows 10 from outside of Windows

Clearly there is no way to format Windows 10 system partition within Windows running. Thus, you can format system partition from somewhere other than your Windows installation. Here comes two ways to format the system drive in Windows 10.

Note: As mentioned before, formatting will erase all data on the selected partition, so please back up important files to safe places, such as cloud storage, other partitions, and external drive.

1. Format C drive with Command Prompt (Windows setup media required)

If you have a Windows installation media (no matter Windows 7 or Windows 10), you can format windows 10 system partition by accessing it.

Step 1. Boot from the Windows Setup DVD (here takes Windows 7 setup DVD). Watch for the Press any key to boot from CD or DVD... Or Windows is loading...message.

Step 2. Wait for the Windows is loading files... and the Starting Windows screens. When they end, you should see the big Windows 7 logo with several drop-down boxes.

Change any Language or Keyboard optionsif you need to and then click Next.

Step 3. Click Install now button, and then, wait during theSetup is starting... Screen.

Step 4. Check the box next to “I accept the license terms”, and click Next.

Step 5. Click on the Custom (advanced) button.

Step 6. Here you will move to “Where do you want to install Windows?” window. And this is where you’ll be able to format C drive of Windows 10. Click the Drive options (advanced) link under the list of hard drives.

Step 7. You can see that several other options are now available including Format. And now, you can format system partition on the disk Windows 10. Choose the partition from the list that represents your C drive and then, click the Format link.

Format C Drive

Step 8. After clicking Format, you’re warned that what you’ve formatting might contains recovery files, system files, or important software from your computer manufacturer. If you format this partition, any data stored on it will be lost. Click OK.

Note: Your cursor will turn busy while Windows Setup is formatting the drive. When the format is over, you can remove the Windows Setup DVD and turn off your computer.

2. Format C drive Windows 10 with freeware

Apart from formatting C drive Windows 10 using Command Prompt accessible from outside of Windows via a System Repair Disc, you can also turn to a free partition manager: AOMEI Partition Assistant Standard, which can help you create a bootable media, and format C drive on the disk of Windows 10 easier via the media you created.

Download Freeware Win 10/8.1/8/7/XP
Secure Download

1). Prepare an external hard drive or flash drive, connect it to your computer, FREE download AOMEI Partition Assistant, install and launch it. Then, you can click Make Bootable Media to create a bootable CD or USB disk.

Make Bootable Media

2). Then, boot the computer from the created bootable media. Then, right click on the system partition, select “Format Partition”.

Format C Drive

3). Choose a proper file system for the C drive and click "OK".

Choose File System

4). Finally, click Apply to execute the task immediately.

Apply

AOMEI Partition Assistant is a great partition manager that can totally replace Windows Disk Management. You can use it to resize partition, create partition, delete partition, format partition, etc. Besides those basic functions, it has many advanced features, like migrate OS to SSD, you can upgrade to AOMEI Partition Assistant Professional to get more.