Why is the hard drive the C: drive?

On computers running Windows or MS-DOS, the hard drive is labeled with the C: drive letter. The reason is because it is the first available drive letter for hard drives. The computer reserves A: and B: drive letters for the floppy disk drive and removable media, such as tape drives, even if these devices are not installed in the computer. As you install other drives and create new partitions, they are assigned to other drive letters after C, such as D, E, F, G, etc.

For example, today, most desktop computers and some laptops come with a hard drive and a disc drive, such as a DVD drive or DVD writer drive. With this common configuration, the C: drive would be assigned to the hard drive and the D: drive would be assigned to the DVD drive. Even if a floppy drive is not installed, because A: and B: drive letters are reserved for floppy drives, the C: drive is still assigned to the hard drive.