The C drive and D drive are both partitioned volumes of a physical hard drive; however, each volume is treated as a separate entity by the operating system. Most computer manufacturers use the C drive to store the operating system and other applications while the D drive is used as the recovery disk.
Computer users can create additional volumes on the hard disk. However, there must be additional space within an extended partition or unallocated disk space before a partition can be created. Unallocated space can be created by either deleting an entire volume or shrinking an already existing volume. Disk partitioning can be done using the disk management tool or third party applications.