Unallocated space is part of disk space that is not belong to any partition. However, it doesn't mean it's blank. If there are files once saved to this area, they still can be recovered by some tools. To save new files to this area, you must create new volume with this Unallocated space and format with a file system.
Besides creating new, you can add Unallocated space to C drive or other volume. Disk Management of Windows Server 2008 and subsequent versions can help you under some condition, but because of some inherent limitations, it is not the best tool. In most cases, you need to run disk partition software. This article introduces 3 ways with detailed steps to add Unallocated space to system C drive.
To get Unallocated space you may either delete or shrink a volume. If you got Unallocated space by deleting the contiguous partition D, follow the steps to add Unallocated space to C drive with Disk Management (without any software):
Do not delete drive D if you installed programs into it.
If drive D is Logical, its disk space will be converted to Free instead of Unallocated. In that case, Extend Volume is grayed out for C drive after deleting D.
If you got Unallocated space by shrinking D or other partition, Disk Management cannot add Unallocated space to C drive. Because Extend Volume can only merge Unallocated space to the left contiguous partition. Unallocated space shrank from D drive is nonadjacent to C, so Extend Volume is disabled.
Follow the steps to add Unallocated space to C drive after shrinking D:
If the right contiguous partition is E in your computer, simply replace D with E in the steps above.
In some computer, there's not enough free space on the same system disk, but there's large amount on another data disk, many people want to add Unallocated space to C drive from this data disk.
In fact, neither Windows Disk Management nor 3rd-party software can do this. In this situation, you need to copy system disk to another larger one, additional disk space will be shown as Unallocated and it can be added into C drive.
Windows native Disk Management can only add Unallocated space to the left contiguous partition, so it is useless if you cannot delete the right contiguous partition. 3rd party software is better choice to accomplish this task, however, remember to back up first and run safe partition editor tool.
Better than other software, NIUBI Partition Editor has unique 1-Second Rollback, Cancel-at-well and Virtual Mode technologies to protect system and data. In addition, thanks to its special file-moving algorithm, it saves much time while moving D and other partitions. It is very helpful especially to a server. As a disk partition management toolkit, it helps do many other operations.