EMZETT.Optical drives
In short: Devices that read, and partly write, CDs, DVDs and Blu-rays with a laser. Also called CD, DVD or Blu-ray drives and burners.
In more detail: A motor spins the disc and a sled moves the laser unit radially across the track. The reflected light hits a photodiode; the changes in brightness (pits and lands) become bits. A control loop keeps focus and tracking even if the disc wobbles slightly.
In Depth
Connection
Internal drives today mostly connect via SATA, older ones via IDE. External drives connect via USB. Notebooks rarely have them built in; a USB drive is the usual solution for old discs.
Burners and speed
When burning, a stronger laser heats individual spots of the dye or alloy layer. Too high a burn speed and cheap blanks often cause errors. When reading, error correction and repeated re-reading are the reason why scratched discs get slow.
Problems
Typical causes of faults: dirty lens, old belt, weak laser. A scratched CD-ROM can sometimes be read in a second drive or copied with special programs. Important data belongs additionally on a hard disk or SSD.