By AOMEI / Last Updated June 8, 2020

Which circumstance will you see the message?

When you use AOMEI Partition Assistant, some operations require that there must be some unallocated space on hard drive. In general, there are two operations that require an unallocated space:

Copy Partition: It is function that copy data and files from one partition to other location. In the process of operating, this wizard requires the destination location must be an unallocated disk space.


Migrate OS to SSD or HDD: It is the function that transfers/clones system drive to from an old HDD to a new SSD or HDD. And the destination SSD or HDD must have an unallocated disk space.


How to create an unallocated space?

In many computers, all space will be allocated to partitions. Hence, how to split an unallocated space out of existing partitions? AOMEI Partition Assistant professional will help you solve this problem. It allows you to shrink or delete a partition to generate unallocated space in Windows 10, 8, 7. Here are the steps in detais.

Way 1: Shrink A Partition

If a partition on disk has free (unused) space, you can use "Resize Partition" to shrink partition, and then the free space on the partition will become unallocated space. Right click any partition (here take E partition for example) which has free space, and select "Resize Partition".

Resize Partition

A pop-up window will appear, and drag slider bar leftwards. Then, you can click "OK".

Drag To Left To Shrink

Now you can find that there is an unallocated disk space behind the partition E. To save the change, please click "Apply".

Apply Resize Shrink

Way 2: Delete A Partition

Deleting a partition can also create an unallocated space. However, before deleting a partition, please remember to backup data or transfer files on the partition to other location. The operation of deleting partition is very simple.

Right click the partition (here take G partition for example) that you want to delete and select "Delete Partition".

Delete Partition

In the pop-up window, there are two ways available to delete partition. To save your time, please tick the option "Delete partition quickly" and click "OK".

Delete Efi Quickly

Now you can find that partition G changes into unallocated space. To save the change, please click "Apply".


Good to know

How to clone data to a unallocated space on a HDD or SSD in Windows 10, 8, 7? The size of the unallocated space is one of the most important consideration. There are two methods to copy partition or hard drive, which you can choose according to the unallocated space on the cloned drive. .

  • Copy Partition Quickly: only copy the used space of the partition, and supports to resize partition during the copy process (Recommend).If you choose this method, the unallocated space could be smaller than thesource partition but MUST be larger than the used space of source partition.

  • Sector by Sector Copy: copy all sectors of the partition to another disk, no matter it is used or not. If you choose this method, please make sure the unallocated space is equal or larger than source partition.