Add a New Partition to an Existing Drive


Occasionally, it may be necessary due to software requirements, company policy, or interoperability requirements to have a hard disk drive partition with a particular drive letter other than the default assigned by Microsoft Windows. Normally, drive lettering works as follows:

A: Primary Floppy Disk Drive (this drive letter is typically skipped if there is no floppy disk drive installed)
B: Secondary Floppy Disk Drive (this drive letter is typically skipped if there is no floppy disk drive installed)
C: Primary Hard Disk Drive, SSD, or whatever media Windows is installed on
D: Secondary Hard Disk Drive or Optical (CD or DVD) Drive
E: – Z: Additional Drives, Removable Drives (USB, etc.), Mapped Network Drives (though network drive mapping is no longer recommended; UNC paths are now preferred)


If it is not practicable to install a new physical drive or reassign the drive letter of an existing storage device, some of the free space on an existing drive can be converted into a new partition with the drive letter of your choice. In this example, we will carve out some available disk space on drive C: and assign it the drive letter D:.


Begin by right-clicking on the Start button and clicking Run.

Type “compmgmt.msc” into the Run box and click OK or press Enter.

Select “Disk Management.”

Right-click on drive C: and click “Shrink Volume…”

A “Querying Shrink Space” popup will appear for some time.

It’s not recommended to use quite all of the available space as this might make drive C: too small to install programs, store files in your user’s home folder, etc. It is best to try to determine ahead of time the smallest usable size for the new partition and go with that. In this example, the original disk was 80GB, quite small by modern standards, and the amount of space to shrink (i.e. the space that will become the new partition) was reduced from the maximum by a few gigabytes.

The disk will now show the unused portion.

Right-click on this unused portion and click “New Simple Volume…”

Click Next to begin the New Simple Volume Wizard.

This time, use all available space so nothing is left unused on the disk.

Assign the drive letter you require. Any available letter can be selected, but in this case D: is used.

The default format options should be acceptable, though it is common to blank out the Volume label or give it a more descriptive name.

Click Finish to complete the wizard.

It may be necessary to refresh the Disk Management view, but the new drive letter should appear on the new partition.

The new partition should now appear with its own drive letter in File Explorer.


Selecting an appropriate size for the new partition can be difficult, as it could result in an unusable amount of free space remaining on the original partition. While it is possible to start over by removing the newly created partition, extending the original partition and beginning again from scratch, once data is on the new partition it becomes increasingly difficult to make any more adjustments.