Many people may know Windows has a subst.exe command which allows you to temporarily substitute a folder on your computer for another drive letter.

Windows 7 (may be available on other operating systems too, it’s probably alway been there but I’ve not noticed it before!) has an additional interesting feature that lets you map a complete hard drive to a virtual folder on another drive. Assuming you have two drives in your computer, To enable this, first go to Control Panel > System and Security > Create and format Disk Partitions. This loads up the disk management console:

From here, right click on the drive you want to mount as a virtual directory, and select ‘Change Drive letter and paths”:

To mount a partition as a virtual directory first the existing drive assignment must be removed. Click on the existing drive letter and select the Remove button. Assuming you’ve read the warning about removing a drive letter assignment and clicked yes to remove, enter the drive letter assignment menu again, and this time select the ‘Add’ button. (Tip: you must create a directory first, click the New Folder button under the Browse for directory dialog to create one.)

Click ok and open Windows explorer. It is now possible to see this directory as a linked folder:

This is especially useful to extend the space on an existing machine while not requiring operating system upgrades, re-installs and so on.