CD's and Hard Disks

CD:
A CD is optical media because it uses light. The CD has three layers, the front, the back which is a metallic surface and another layer of plastic pressed onto it. CD's hold approximately 700 mb. When the laser reads the CD, it sees if the light bounces back or not. If it bounces back then it's a zero. If not it's a one. This is how CD's store data in binary language. To connect with computers the CD uses a Integrated Drive Electronics (IDE) interface.

Hard Disk:
A hard disk is manetic media because it uses magnets. Hard disks are a metallic platter which has billions of magnetic receptors on it. Since magnets have two poles, north and south they can be used to represent binary language zeroes and ones. The actuator arm is a metal arm that reads the disk as it spins.