The optical drive uses a laser to read from and record data onto optical discs. A laser-emitting diode is used to create the laser beam. In drives like the combo drive, two laser diodes are used, and depending on the nature of the media, the appropriate laser is used.

Leadin
This refers to the additional information that identifies the data written in a session. The Lead-in contains a Table of Contents, which has a list of files written in the session.