Have you heard about new compact Discs? They're the latest invention from Sony. A CD consists of a piece of aluminium coated with transparent plastic，12 cms across，for producing sound. It's similar to an ordinary record，except that it's read by a laser beam，and the information recorded on the aluminium is digital. The makers claim that a CD can reproduce the original sound perfectly，without any distortion or background hiss. As the system is computerized，there's no loss of quality between the studio master and the record you buy. Also，a CD is much tougher-than a vinyl(乙烯基)record，so it doesn't need such careful handling. Dust and dirt won't damage it，and as there's no contact between the laser and the disc, it will never wear out.