Cannot extend C drive with Unallocated space

By Allen, Updated on: December 24, 2019

This article introduces why Disk Management cannot extend C drive with Unallocated space and what to do if unable to expand system partition with this native tool.

Applies to: Windows 10, Windows 8, Windows 7, Windows Server 2019, Windows Server 2016, Windows Server 2012 (R2), Small Business Server 2011, Windows Server 2008 (R2)

Low disk space is common issue to all computers running Windows Operating System. If you use Windows XP or Server 2003, you have to back up, delete and recreate all partition, finally restore everything. From Windows 7 and Server 2008, there are new Shrink and Extend Volume functions added in Disk Management console. Many people try to extend C drive by shrinking D or other volume. But unfortunately, system C drive cannot be extended after shrinking any other volume. This article introduces why cannot extend C drive with Unallocated space in Disk Management and how to fix this issue.

Why cannot extend system C drive with Unallocated space

In fact, Disk Management can only shrink and extend NTFS partition, FAT32 is not supported. However, it is not an issue to system C drive, because it is formatted as NTFS by default. The most common reason why unable to extend C drive with Unallocated space is because this space is nonadjacent.

From Microsoft explanation, Extend Volume functionality only works when there is adjacent Unallocated space on the right side. When you shrink drive D with Shrink Volume, Unallocated space can only be made on the right side of D, so it is non adjacent to drive C.

To show you the truth, I shrank D drive with Disk Management in my Windows 10 laptop.

Extend Volume greyed out

As you see:

The only way to enable Extend Volume for system C drive is by deleting the right contiguous partition D. But in most of computers, D drive is used for programs and Windows services, so it can't be deleted.

What to do if unable to extend C drive with Unallocated space

In this situation, you need 3rd-party software to move Unallocated space next to C drive. Among these software, NIUBI Partition Editor has free edition for Windows 10, 8, 7, Vista, XP home computers. The most important, it has unique 1 Second Rollback, Virtual Mode and Cancel-at-well technologies to protect system and data. In addition, it is much faster because of the special file-moving algorithm. This is very helpful if there are large amount of files in the right contiguous partition D.

How to fix the issue cannot extend C drive with Unallocated space in Disk Management:

  1. Download NIUBI Partition Editor, right click drive D and select "Resize/Move Volume", drag middle position towards right in the pop-up window, then Unallocated space will be moved to the left side.

    Move drive D

    Move Unallocated space

  2. Right click drive C: and select "Resize/Move Volume" again, drag right border towards right in the pop-up window, then Unallocated space will be merged into C drive.

    Extend C drive

    Extend C drive

  3. Click Apply on top left to take effect. (All operations before this step only work in virtual mode.)

Watch the video how to move Unallocated space and combine to C drive:

Video guide

Because of the limitation of Extend Volume, Disk Management cannot extend C drive with Unallocated space that shrunk from D or other partitions. With NIUBI Partition Editor, you can move and add Unallocated space to C drive easily and safely. It also helps you do many other disk and partition management operations.

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