If you have a hard drive with some unallocated space on the end of (i.e. not currently assigned to a partition) and want to use that space to add to an existing partition, a simple and effective tool you can use is Diskpart. This tool is included with Windows XP and later.

The documentation is pretty easy to follow, but for example suppose you want to extend the size of your E drive with some empty space on the end:

1. Make sure you have your data backed up (just in case)
2. Open a command prompt as the Administrator
3. Type ‘diskpart’
4. Type ‘list disk’ to get the disk number of the drive
5. Type ’select disk=[disk#]‘
6. Type ‘list partition’ to get the partition number of the partition to extend
7. Type ’select partition=[partition#]‘
8. Type ‘extend’
9. Once the command completes, your E drive is now resized to include the additional empty space

Note: You cannot use this to resize the active system drive (usually C), so if you do need to resize your C drive, you would need to remove the hard drive from the computer and plug it into another computer where it is not the C drive. Once you do this you can then resize it.

This also works in virtual machines, so you can use this in combination with the VHD Resizer tool to completely manage your VHD files.

While there are certainly more user friendly and feature-rich products available, this tool does the job quickly and easily.