By Cherry / Last Updated April 24, 2020

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 format C drive is an ideal way to clean system partition for reinstalling system while keeping all the data on other partitions safe.

However, it is very much not a straightforward process to format C drive. It is different from 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”.

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 provides you top two ways to format C drive 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 from a Windows setup disc or flash drive

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

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

  • 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.

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

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

  • Click on the Custom (advanced) button.

  • 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.

  • 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.

  • 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.


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 system repair disk

Format C drive Windows 10 by using the format command from Command Prompt, accessible from outside of Windows via a System Repair Disc. But first, you need to create a Windows 10 system repair disc.

To create system repair disc, here you can take use of a tool named AOMEI Partition Assistant, which can help you create system repair disc, and format C drive on the disk of Windows 10 easier via the system repair disc you created.

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.


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.