|So the entire space is not currently in use. If you had any files stored on the unallocated portion you may need to use a file recovery program to recover them. |
You can partition the unallocated portion of the pen drive and then format it. You will then be able to use the full amount of space.
Do you use the pen drive for othe operating systems, or for oler Windows versions? If not, you should be using NTFS file system.