Why do disk letters start with C:? When my nephew asked me this he was 20 years old and I knew I was getting old. In the late days of floppy disks the first 2 drives were always the (removable) disk drives A & B. Only later computers started to get hard disk drives that were built into the machines and as such they got the next letter: C. A long time ago on Windows it could even generate issues if you would assign custom drives to the letters A: and B: because Windows still expected floppy drives there. Often you would end up partitioning a hard disk having the Windows operating system partition on C:, the optical drive on D: and then multiple partitions more on letters later in the alphabet. These days are gone. At least I got accustomed to put the optical drive on A: and an external hard disk on B:. The hard disk partitions start at C: and go throughout the letters in a more logical fashion. (and today you usually anyways just have one optical drive, not a dedicated CD-...