D Drive VS C Drive (Everything to Know)

If you don’t have a clear understanding of D drive and C drive in Windows 11, 10, 8, 7, this post can help you learn all differences between D drive and C drive through a comprehensive comparison.


By Emily / Updated on May 12, 2023

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D drive VS C drive

C drive and D Drive are two common partitions in Windows operating system. The C and D are called drive letters of the partitions. They are used by the Windows to mark each volume, which can help simplify the daily disk partition management. As for the specific difference between C drive and D drive, please read on.

What is local disk C drive?

The C drive is the main disk partition where the operating system is installed and all the crucial system files are stored. C letter is the first available drive letter for the disk partitions, then many users may wonder why it starts from C, where the A and B letter goes. That’s because the computer reserves A: and B: drive letters for the floppy disk drives, even if these devices are not installed on the computer.

What is D drive?

A and B are kept by Windows for floppy disk drive and removable media, and C is assigned to the system partition, so when you install other drives and create new partitions, they will be assigned to other drive letter after C, such as D, E, F, G, H, and so on. However, sometimes, you may find D letter is not available when choosing a drive letter for a new partition.

So, why the D is missing? In such cases, it might have been assigned to devices which are removed or hidden. You check for any hidden devices and remove them to assign the missing drive letters: open "Device Manager"->"View"-> "Show hidden devices", look for the hidden devices under "storage volumes" and "portable devices". then right click on the hidden device and click on "uninstall", finally restart the computer.

View Hidden Devices


Can you switch C drive and D drive letter?

A drive letter is just an alphabetic character to identify a physical computer disk or drive partition, so some users want to know if it is safe to change the drive letter. Generally speaking, it is not a wise idea to change the drive letter of the partition where Windows or applications are installed. If you insist on doing that, the OS or Apps might have trouble finding the drive and running successfully. As a result, you would likely need to reinstall those programs or OS from scratch.

So, we suggest that you don’t change the drive letter of a drive which contains OS or apps, namely the C drive and D drive since the OS is installed on C drive and applications are on D drive in most situations.

What happens if the C drive is full?

As mentioned above, the C drive is always the system/boot partition, so it is very important for the computer to function smoothly and properly. If the C drive gets full and runs out of the space, the system will start to develop some issues:

♦The operating system and applications will take forever to boot, and the files will take a long time to load.

♦You cannot install any software updates and apps or they will be installed imperfectly.

♦When you start an intensive operation on your computer, it might freeze or crash because there is not any virtual memory left.

How to solve "C Drive is Full" Issue in Windows?

As it is well-known that full C drive can trigger many serious issues, you may want to know what can help with that. In general, you can try freeing up the C drive space, or adding more space to C drive. No matter which way you finally go with, the AOMEI Partition Assistant Professional can be a nice tool. Below come more details.

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Section 1. Free up C drive space

For this task, apart from deleting temporary files, caches, running Disk Cleanup, uninstalling apps, you can try moving some large applications from C drive to another drive like D drive via AOMEI Partition Assistant software. This can make a big difference when all applications on C drive are necessary and cannot be uninstalled.

 Step 1. Install and launch PA Professional, then select the “App Mover” under "Free up".

Click App Mover

Step 2. In the pop-up window, select C partition and click "Next".

Select Partition

Step 3.Now, all applications that can be moved out from C drive will be listed. Choose one or more apps and select a destination partition. Click "Move" to execute the operation.

Tick Apps

Step 4. Make sure that you have closed apps that will be moved. Then, click "OK".


Step 5. Wait for the process to complete. Then, click "Finish".


Afterwards, the C drive can gain more unused space for new data.

Section 2. Add more space to C drive from other drives

If you don’t want to delete or move anything on C drive, you can also use this software to enlarge C drive space by taking some unused space from other partitions. Its "Allocate Free Space" is just designed for this job, easy and powerful.

Step 1.Right-click the partition that has enough free space and select "Allocate Free Space".

Allocate Free Space

Step 2. Type in the size of the free space and choose C drive as the destination partition.

Allocate Free D to C

Step 3. Click "Apply" to execute this operation.


See? Just three steps can add more space to C drive. If there is already some unallocated free space on the disk, you can also use the "Merge Partitions" to add it into C drive.

Merge Partitions


Getting more info about D drive vs C drive can help you better partition your hard drive. A proper disk space allocation can secure your computer from encountering problems like Windows OS slowing down, or becoming extremely low, insufficient storage space for new data, windows updates. If those issues happen someday, don’t worry since the AOMEI Partition Assistant Profession is able to help fix that easily. If you are using Windows Server OS, please go for the Server edition.

Emily · Staff Editor
Emily is an English editor of AOMEI Technology; she has a great passion for providing easy solutions for people to tackle with all disk or partition management problems. In addition to writing articles about disk/partition management, she also edits great tutorials on how to back up and restore disk for data security. In her spare time, she loves to learn computer skill to improve herself or stay with her family to enjoy a good day.