What are drive letters?
Drive letters are labels assigned to storage devices connected to a computer. They allow the operating system to identify and access the devices (Source). Drive letters start with A and B, which were reserved for floppy drives on older systems (Source).
Default Drive Letter Assignments
On Windows computers, the boot drive with the operating system installed is usually assigned the letter C. This is the primary hard drive that contains the Windows system files.
The letter D is often assigned to additional storage drives added to the computer. Some common devices that may be designated as Drive D include:
- A second internal hard drive
- An optical disc drive like a CD, DVD, or Blu-ray drive
- An external drive connected via USB or eSATA
- A flash or thumb drive plugged into a USB port
So Drive D is simply the next available letter after the C drive and can refer to any secondary storage drive added to your computer system. The exact device will depend on your PC’s configuration.
Finding available drive letters
When a new drive is connected to your computer, it is automatically assigned the next available drive letter. To view all drive letters currently in use on your system, you can open the Disk Management utility:
1. Press Windows Key + R to open the Run dialog box.
2. Type diskmgmt.msc and click OK to launch Disk Management.
In the Disk Management window, you will see a list of all your drives and their assigned drive letters. Typically, drive letters start at C and go through Z. Drive letters A and B are reserved for floppy disk drives. The drive letters towards the end of the alphabet are usually available for allocating to new devices.
So if you already have drive letters C through F in use, the next available drive letter would likely be G or later in the alphabet. Knowing the last assigned drive letter can help you identify where new devices may show up.
You can also use the Get-AvailableDriveLetter PowerShell cmdlet to return an array of all available drive letters on your system.
Changing an existing drive letter
Drive letters in Windows can be changed through the Disk Management utility. However, care must be taken to ensure the new drive letter is not already assigned to another drive.
According to How to Change a Drive Letter in Windows 10 – Alphr, the steps to change a drive letter are:
- Open Disk Management (right-click the Start menu and select Disk Management)
- Right-click the drive you want to change the letter for and select Change Drive Letter and Paths
- Click Change to choose a new drive letter
- Select a new drive letter from the dropdown that is not already in use
- Click OK to confirm the change
The key is to avoid selecting a drive letter already assigned to another disk, as this will result in one of the drives not being accessible. Checking which letters are free beforehand avoids this issue.
With a few clicks in Disk Management, the drive letter can be altered to any available letter in the alphabet. Just be sure no other drives are already using that letter to prevent conflicts.
Drive D Is Missing?
If Drive D is missing from your computer, there are a couple potential causes:
The drive may have become disconnected. If Drive D was assigned to an external drive like a USB flash drive or external hard drive, it’s possible the drive was unplugged or disabled in Device Manager. Check your connections and make sure the external drive is being detected properly.
The drive letter may have been changed accidentally. Drive letters can sometimes change, especially if you connect new devices. Check in Disk Management to see if D is now assigned to a different drive. You may be able to change it back if needed.
Drive letters can also be hidden in Disk Management. Make sure D is not simply hidden from view. Right-click on a visible drive and select “Change Drive Letter and Paths” to show any hidden letters.
If Drive D was assigned to a network share or optical drive, it may no longer be connected. Check for connectivity issues or troubled devices.
Finally, Drive D may be having hardware problems if it was an internal drive. Check in Disk Management to see if the drive shows errors or needs to be formatted. Back up data and run hardware diagnostics if D keeps disappearing.
With some basic checks, you should be able to locate and restore your missing Drive D.
External drive as Drive D
External USB hard drives connected to a Windows PC will often default to being assigned the letter D. This is because drive letters A and B are usually reserved for floppy disk drives, C is the system drive, and D is the next available letter.
The specific drive letter assigned can vary depending on the number of partitions and drives already connected. If the letter D is already in use, the external drive may get assigned another letter like E, F, G instead.
If needed, the drive letter for an external drive can be changed in Windows. To do this, right click on the drive in File Explorer, select “Change drive letter and paths”, then choose a new available letter. This Microsoft forum post has more details on changing drive letters in Windows.
Changing the letter for an external drive to be consistent across computers can prevent issues accessing the same drive from multiple devices. However, the changed letter may revert if the drive is connected to another PC that already has that letter assigned.
Optical drives as Drive D
It’s common for optical disc drives, such as CD or DVD drives, to be assigned the letter D on Windows PCs. This is because the default drive letter order assigns A and B to floppy drives (rarely used today), C to the primary hard drive, and D to the first optical drive detected by the system.
So if you don’t see a D drive but notice you have a DVD or CD drive listed in Windows, chances are that optical drive has been assigned the D letter. You can check this in Disk Management: press Win + R, type “diskmgmt.msc”, press Enter. This will show all drives connected to your PC, including their assigned drive letters.
If the optical drive shows as D here, then there’s your D drive. It likely doesn’t appear as a separate drive in File Explorer by default because optical media like CDs/DVDs are treated as separate removable volumes instead. But the drive itself still occupies the D letter.
If you need to change the drive letter assigned to the optical drive, you can do so in Disk Management. Just right-click on the drive listing and choose “Change Drive Letter and Paths”. This will allow you to assign it a different letter if needed.
Network Locations as Drive D
Mapped network drives can appear as drive letters in Windows. This allows you to access files and folders on a network share through a drive letter, similar to a local disk drive on your computer. Network locations mapped as drive D allow you to conveniently interact with that location as if it were drive D (citation: https://support.microsoft.com/en-us/windows/map-a-network-drive-in-windows-29ce55d1-34e3-a7e2-4801-131475f9557d).
To map a network drive as drive D, open File Explorer, right click on This PC or Network, select “Map network drive” and choose the drive letter D for that network location (citation: https://www.tenforums.com/network-sharing/78219-i-need-map-drive-d-drive-another-computer.html). The network share will then appear as drive D and allow you to easily access files just like on a local drive.
Mapping network locations to drive letters like D is useful for conveniently accessing network shares and files across different devices on a network. It eliminates the need to navigate network paths each time, making remote network locations feel like local drives on your computer.
Flash drives as Drive D
Removable devices like flash drives and USB sticks are commonly assigned the drive letter D when plugged into a computer. The specific drive letter assigned depends on what other drives are currently connected and which letters are available at the time the flash drive is plugged in.
For example, if your computer has its main hard drive as C and a CD/DVD drive as D, then when you plug in a flash drive it may show up as E or another available drive letter. However, if no CD/DVD drive is present, the flash drive is likely to take the D drive letter.
So if your flash drive normally shows up as D on your computer, but is missing or showing up as something else, it could mean another device is currently assigned D or there are issues with the flash drive itself. Check your other connected drives and try disconnecting/reconnecting the flash drive to troubleshoot.
For more details, see this article on portable file links.
Troubleshooting drive letter issues
If you are having trouble with drive letters not displaying correctly or being unassignable in File Explorer, the main tool to diagnose and resolve these problems is Disk Management.
To open Disk Management in Windows 10 or 11, right click the Start menu and choose “Disk Management”. This will open a window showing all your drives and their assigned letters.[1]
Here you can see the drive letters that are currently in use on your system. If a letter is missing or not displaying correctly, you can try to change it here. Right click on the disk and choose “Change drive letter and paths”.
This will allow you to modify the drive letter assignment if there is a conflict with another device. For example, if you have an external drive using D, you can change it to another available letter.
Disk Management is the main troubleshooting tool for diagnosing drive letter problems in Windows. Changing the letters here can often resolve conflicts and issues that prevent a drive from displaying the correct letter.