Why is the hard drive the C: drive?
On computers running Windows or MS-DOS, the hard drive is labeled with the driver letter C, because it is the first available drive letter for hard drives. The computer assigns the A: and B: drives to floppy disks, and removable media such as tape drives. As you install other drives, create new partitions, they will be assigned to other drive letters after C, such as D, E, F, G, etc.
For example, most computers today come with a hard drive and a disc drive, such as a CD-ROM, CD-R, or DVD drive. With this common configuration, the C: drive would be assigned to the hard drive and the D: drive would be assigned to the CD or DVD drive. Even if a floppy drive is not installed in the computer, because A: and B: drive letters are reserved for floppy drives, the C: drive will still be assigned to the hard drive.