An optical drive is a computer disc drive that uses a laser to read optical discs like CDs, DVDs, and Blu-rays. Optical drives are available in both internal models that are mounted inside a computer and connected directly to the motherboard, as well as external models in separate enclosures. Most optical drives can not only read optical discs, but can also write to writable and rewritable discs.
The word "optical" means "relating to vision or light." In the case of optical drives and optical media, it refers to the laser that reads the underside of a spinning plastic disc, detecting a series of bumps and pits that contain encoded digital data. Optical drives that can write to discs include several lasers at different levels of power — a low-power laser that reads data, a medium-power laser that erases rewritable discs, and a high-power laser that burns data to a disc.
Each new generation of optical media uses narrower lasers to read smaller bumps and pits — a CD contains pits 800 nm long, while a Blu-ray disc's pits are only 150 nm long. The speed at which an optical drive can read the pits on a disc depends on how fast the disc is spinning — a Blu-ray optical drive, for example, can spin a disc at more than 9,000 revolutions per minute while reading data. Even when a disc is spinning that fast, optical drives are still slower than hard drives and solid-state drives. However, since optical media is inexpensive and removable, it is most often used to distribute large amounts of data, particularly high-definition movies and console video games.