By Lily / Last Updated June 12, 2020

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Warning: C drive becomes red

During the usage of a computer, applications keep being installed into Windows system. One day, you may get mad at your computer because you have to wait for extra time when you try to launch an application or close it. It is absolutely annoying! And when you open “Computer”, you’ll find that C drive becomes red.

C Drive in Red

It is a warning that you are running out of disk space on C drive. You are supposed to delete old and unnecessary files in order to make more free space. However, it proves useless when the problem comes again after a short period of time. Now you must be searching for a more effective way—increasing memory of C drive. If you don’t know how to increase disk space in C drive safely, move on to the next part.

How to increase memory of C drive effortlessly in Windows 7/8/10?

To optimize computer performance by increasing memory of C drive, there are three effective methods at hand.

Method 1: increase memory of C drive using Disk Management

As Disk Management is familiar to most computer users, what comes to you first is how to extend C drive using Disk Management. Follow the steps below:

1. Right-click the “Computer” icon on the desktop and hit the “Manage” option.

2. Click on “Disk Management” to open Windows Disk Management.

3. Select C drive, right-click and hit “Extend Volume”.

Disk Management

4. Set the amount of space to be extended to C drive following Extend Volume Wizard.

Extend Volume Wizard

Tip: The “Extend Volume” option can be greyed out if there is no contiguous unallocated space on the right side of C drive. On that occasion, if there are other partitions on the same disk, you can choose to delete the adjacent partition to create unallocated space but you must make sure your crucial data have been backed up before that. The process might be time-consuming and error-prone.

Method 2: increase memory of C drive with Diskpart

Some people prefer to increase C drive space with Diskpart. Then, do following steps:

1. Press Windows Key + R to open the Run dialogue. Type diskpart and click “OK”.

2. Type list volume and press Enter.

3. Type select volume # (ex: Volume 1) to select C drive that you want to extend and press Enter.

4. Type extend size=# (ex: size=2048) to extend C drive by size in megabytes (MB) and press Enter.

5. Type exit and press Enter to exit Diskpart.


● You may fail to extend C drive if there is no contiguous unallocated space on the disk.
● If you do not specify a size, C drive will be extended to take up all the contiguous unallocated space.

Method 3: increase memory of C drive via a handy software

Now you see the limitation of extending C drive with Disk Management and Diskpart. Here comes a handy partition manager— AOMEI Partition Assistant Professional. It helps you increase memory of C drive as long as there is unallocated space on the same disk, whether it’s right behind C drive or not. I’ll tell you how to increase C drive space in Windows 7 without formatting via AOMEI Partition Assistant in detail. It also applies to other Windows operating systems, like Windows 8/10, etc.

Step 1. Launch AOMEI Partition Assistant. Right click C drive, select “Merge Partitions”.

Merge Partitions

Step 2. Find unallocated space, tick in the box and click “OK”.

Add Unallocated Space to C

Step 3. Confirm “Pending Operations” and click “Apply” to execute the operation.


Tip: You can see clearly from Step 1 that the unallocated space lies behind D drive instead of C drive. By “Merge Partitions” option, the unallocated space will be moved and added to C drive automatically.

▶ Increase memory of C drive via Command Prompt

1. You can also use AOMEI Partition Assistant command lines to extend C drive. Just input following command lines and press Enter after each:

cd C:\Program Files (x86)\AOMEI Partition Assistant Pro Edition 7.0 (You should change the path after “cd” with the installation directory of AOMEI Partition Assistant on your computer.)

partassist.exe /list

Partassist List

partassist.exe /resize:C /extend:1024 (By default, the specified size is in MB, and GB is also available.)

Partassist Extend C

2. For the target partition is system partition, the operation will be completed under AOMEI Partition Assistant PreOS Mode. Wait for the process to be completed and restart your computer after that.

PreOS Mode


If you find your computer works slower and slower, try to increase memory of C drive via three methods mentioned above. However, AOMEI Partition Assistant is a powerful partition manager with more practical features. It can also help you move partitions, allocate free space from one partition to another and so on.