By Emily / Last Updated December 15, 2020

Need to Extend System Partition before Upgrading to Windows 10

The system partition is the primary partition that is used as the active boot partition. It is typically created during the Windows installation process. On most computers, the system partition is the C: drive, around 30GB. With more apps especially the large-sized ones being continually installed onto the boot volume, you may find out the system partition is running out of space and shows red bar in Windows File Explorer.

C Drive Red Bar

If you want to upgrade Windows 7 or Windows 8 to Windows 10, you have to make sure there is about 8GB free space for Windows 10 installation and operation. If there is not enough free space for upgrading to Windows 10 or installing Windows 10, it is quite necessary to extend C drieve before Windows 10 upgrading or installation.

Extend System Partition Greyed Out

The Windows built-in tool, Disk Management, is capable of extending system partition. Open Disk Management; then right-click the C: drive, and click “Extend Volume” to do the rest as instructed. It seems quite convenient to extend system partition before upgrading to windows 10 with the built-in tool Windows Disk Management, but the Extend Volume option might be grayed out in some situations (like the pic below).

Extend C Volume Grey Out

Why? That's because the Disk Management allows you to extend a partition only if there is contiguous unalloated space next to its right side. However, the only way to create the unallocated space needed for extending partition is to delete the partition next to its right side. Besides, the Disk Management only supports extending NTFS partition. If the system partitin is of FAT32 file system, the “Extend Volume” option will also be greyed out.

Easier way to extend system partition before upgrading to Windows 10

When you cannot extend system partition before installing or upgrading to Windows 10 in Disk Management due to its limitations, you can consider using the free partition manager: AOMEI Partition Assistant Standard. It allows you to extend both NTFS and FAT32 (system) partition in all editions of Windows 10, 8, 7 and Windows XP/Vista. Moreover, with the “Merge Partitions” funtion, you can easily extend a partition with any unallocated space on the same hard disk, no matter whether the space is adjacent to the target partition or not.

Now, you can download the freeware and learn to successfully extend system partition in Windows PC. It only takes 3 steps. Quite easy and simple.

☞ If there is not unallocated space, you have to shrink or delete another partition to create such space.
☞Before you extend system partition before upgrading to Windows 10, you'd better defrag the partitions and check disk errors in need of a smooth and quick performance.

1. Install and launch AOMEI Partition Assistant Standard. Right-click the system partition and click ”Merge Partitions”.


2. Tick the unallocated space you want to add into the system partition, and click on “OK” .


3. Back to the main interface, click on “Apply” to commit the pending operation.


This function can also merge two adjacent partitions at one time. You can merge data partition into system drive, but you cannot merge system boot drive into data partition.


With the “Merge Partitions” function, you can easily extend system partition before upgrading to Windows 10, but your computer may need to reboot into PreOS to complete the process. If you do not want to reboot your computer, you can upgrade to Professional and use its “Extend Partition Wizard”. In this way, you can extend your system partition without rebooting unless there are page files or applications running on the involved partition, except system C: drive. Besides, its “Allocate Free Space” allows you to directly transfer some space from one partition to another partition.