CD-ROM drive 
Largely replaced by CD-RW and DVD drives, CD-ROM drives play back CD-ROMs and audio CDs. Each CD-ROM drive consists of a spindle that turns the disc, a laser that flashes onto the disc's uneven surface, a prism that directs the laser beam, and a light-sensitive diode that reads the reflected light. The first CD-ROM drives, referred to as 1X (for single speed), could transfer data at a mere 150K per second. Most CD-ROM drives now range from 16X (2.34MB per second) to 52X (7.62MB per second). Performance differences among drives of different speeds are obvious only when copying large files from CD-ROM, as in software installation.