The user interface that made the iPod popular. Originally using an actual rotating wheel, the wheel was later made touch sensitive, and its rotation was simulated. Buttons at the top, bottom, sides and center of the wheel select menus and functions. See iPod classic and scroll mouse.
The Click Wheels Hang On
As of late 2010, the classic iPods (top) still use the click wheel as does the shuffle (bottom left). The touch and nano (bottom right and middle) migrated to touch screens. (Images courtesy of Apple Inc.)