C Drive V.S. D Drive Speed: Local Disk D is Fater than Local Disk C

C drive V.S. D drive speed and other information about partitions are all in this article. Learn more knowledge about your disk and some methods to reclaim free space on C drive.


By Lucas / Updated on May 12, 2023

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Local Disk D is faster than Local Disk C

Some users find that the speed test shows D drive is faster than C drive. How does this happen? Why C drive has a slow speed? Let's find the reason.

C drive VS. D drive-What is the difference?

C and D drives are both physical hard disk partitioned volumes. They are treated as distinct entities by the operating system. The computer's default setting may be to start the system from the C disk because Windows is installed on it, but this is not required. Though most people leave the defaults alone, you may edit the settings and change the drives if you like.

▶ What is the C drive used for?

Every computer has a physical hard drive where data is stored.

The operating system is installed on the hard drive once you or the manufacturer install it on the computer. The hard drive often contains many partitions for storing data, with the C drive referred to as "Local Disk C" being the active primary disk. The operating system, boot sector, and other critical information are installed on the C drive, and the drive is recognized by your system.

When you turn on your computer, it gathers the information required to boot from the C disk. Other applications and apps are also installed by default on the C disk.

▶ What is the D drive used for?

Usually, the D drive is the first drive following the C drive. The role of the D drive may differ from computer to computer, and it might also be used as a recovery disk by manufacturers. If your computer contains an internal drive and an external disk, the external one may be labeled D by default.

Many individuals make a D drive to store their programs and personal stuff on. Some people feel that isolating personal data from system data on a computer can increase performance and make maintenance easier.

C drive VS. D drive speed

If you feel your PC runs slower but are not sure about it, to find out the exact situation, you can test the drive speed to check whether the read/write speed of the C drive is slower or not. 

As a reliable disk and partition manager for Windows, AOMEI Partition Assistant Professional offers such feature you need. The "Disk Speed Test" can help users effortlessly test drive speed with a clear interface and user-friendly operations.

Consumers don't need to have expert computer skills to grasp varied data. There are two test modes available: Simple mode and Pro Mode. You can select the best option based on your requirements. All data will be meticulously recorded so that consumers may simply view the test results. Furthermore, you may export the test result in three ways: copy to clipboard, export to text, and export to screenshot.

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◤ 1. Simple Mode Test

Step 1. Download and run AOMEI Partition Assistant. Click “Test” in the top toolbar, and choose “Disk Speed Test”.

Disk Speed Test

Step 2. In the new window, you can select a test partition, and “Start Test” in “xxx Mode” which is the default mode. You can stop the test during the test.

Start test

After clicking the "Start Test" button, the software starts to test the speed of the hard disk, and the read and write speeds are displayed in real-time according to the system.

When the test is finished, you can see the read/write speed of the drive you selected.

Step 3. If you need, you can click “Export” to export the result. There are 3 ways: Copy to clipboard, Export to text, and Export to screenshot. You can select a location to save the test result.


2. Pro Mode Test

Step 1. After you click “Pro Mode”, you can see the window of this mode. Select the drive you need to test.

Pro Mode

Step 2. Next to the drive selection is the speed, size, test number, test duration. You can set all according to your needs.

Note: If the device's first disk is an NVMe SSD, everything is set to the default configuration.

Step 3. Then you can set the “Test Mode”, “ Block Size”, “Queue Number”, “Thread Number”.


Step 4. When you start the test, the “Read” and “Write” will show the speed in MB/s.

When the test is over, you can export the result as the xxx Mode.

What can you do if local disk D is faster than local disk C?

If you find that the result of the test shows that your local disk D is faster than the local disk C, there're some possible reasons:

1. If both volumes are on the same HDD, then the D volume that has the lowest sectors will be faster than the C volume. That's decided by the physical location of the volume on the hard drive.

2. The other factor is the fragments. If both drives are on the same HDD, then you should think about this issue. As the system drive, the C drive might have more fragments than the D drive because the frequency of reading/writing operation is higher than the D drive. So, if the first disk is an HDD, then, we suggest you defrag the hard drive to prevent the effect of fragmentation.

3. If the local disk C is on an HDD, while the local disk D is on an SSD, then the D drive might be faster than the C drive. This is because of the different working mechanisms of HDD and SSD.

4. The available size is insufficient. The OS will take up lots of free space on the C drive with daily use. All temp files, update data files, new system data files, and newly created program files will be stored in the C drive. That's why many users find that the C drive is full but the D drive is empty.

Further tips: Release more free space on the C drive

If the C drive speed is slower, releasing some free space can help your system run smoothly. AOMEI Partition Assistant can also do this job for you. With the "App Mover" and "Move Folder" features, you can effortlessly move installed apps to another drive and big file folders to a new place, like the D drive.

"App Mover" can automatically find and relocate all required files (even hidden files) of the target programs. After the move, your relocated programs will also operate smoothly.

App Mover

The “Move Folders” feature allows you to move large files between NTFS drives. 

Two options

To sum up

The end of C drive V.S. D drive speed will be affected by many factors. Different drives have different work in your computer to make sure your OS and other tasks can run smoothly. If there's something wrong, AOMEI Partition Assistant will help you a lot. 

Besides the functions we've mentioned, this tool can also clone disk, migrate OS, convert to GPT… And there’s the Server Edition for you to conveniently manage your Server device.

Lucas · Staff Editor
I prefer peaceful and quiet life during vacation,but sometimes I watch football match if my favorite club performs brilliantly in that season. And I love reading, painting and calligraphy, thus I send my friends festival handwriting cards every year.