Why is Windows giving my hard disk the letter C and not A or B for example?

Wikipedia gives a good explanation about the logic of drive lettering:

Except for CP/M and early versions of MS-DOS, the operating systems assigns drive letters according to the following algorithm:

1. Assign the drive letter A: to the first floppy disk drive (drive 0), and B: to the second floppy disk drive (drive 1), if present.
2. Assign a drive letter, beginning with C: to the first active primary partition recognised upon the first physical hard disk.
3. Assign subsequent drive letters to the first primary partition upon each successive physical hard disk drive, if present within the system.
4. Assign subsequent drive letters to every recognised logical partition, beginning with the first hard drive and proceeding through successive physical hard disk drives, if present within the system.
5. Assign subsequent drive letters to any RAM Disk.
6. Assign subsequent drive letters to any additional floppy or optical disc drives.