Since 2002,the iPod is a brand of pocket-sized ultralight hard-drive based audio players designed and marketed by Apple Computers. Today the iPod comes in a range of models such as the Nano, Shuffle and Mini (discontinued now). All of the models in the iPod family are designed to be user friendly, and can easily be used by young children. Therefore, they offer a simple user interface and a central scroll wheel to browse the iPod navigation system. The scroll wheel has been redesigned for the various models, such as with the Nano. The Nano is so small the wheel used on the previous iPod's wouldn't fit. Unlike portable cassette or cd players the iPod stores media on built-in memory. The older models like the iPod Classic and Mini use a hard drive, while the smaller and more modern iPod Nano, Shuffle and Touch use flash memory.