Most CD drives on the market are single CD drives, and, while you will see some double drives, they are more expensive, require special software drivers, and they lag behind significantly in the processes of incorporating new technology. Externally CD drives have the same jumpers and connectors you would find on an ordinary disk drive. The difference is that a CD drive also has an audio connector to connect to the sound card. CD drives also contain a logic board to control the CD drive and to interface with the motherboard. The bay assembly is the same for all drives so we won't look at that here.
Most CD drives have controls on the outside to connect headphone and control volume.
In terms of the compact disk itself, it is made from a polycarbonate substrate 4.75 inches in diameter and 1.2 mm in width. CDs don't erase if you wave a magnet near them, but they are not indestructible. CDs don't contain tracks like magnetic disks. The tracks of the spiral are separated by a mere 1.6 microns.