The Windows operating system divides your computer's hard drive into specific spaces known as "partitions." Data from one partition does not cross over into another partition unless the user copies it ...

To extend a volume, unallocated space must exist, and the unallocated space must be adjacent to the target partition. In addition, the partition style of the target volume must be in NTFS format. The ...

You may view your hard drive in Disk Management and see unallocated space. The space will be on the hard drive, but Windows cannot use it. It is like having a spare room in your house but locked off.