Functionality
It is used, as the name suggests, for scrolling. It can also be used as a third mouse button by pressing on it. Some modern mice can scroll horizontally as well as vertically, using either a tilting scroll-wheel (introduced by Microsoft) or scroll ball (found on Apple's Mighty Mouse). Logitech MicroGear mice (like the MX Revolution and the VX Revolution) use a 14 gram scroll wheel which can preserve the moment of inertia like a flywheel and can be used to quickly scroll through long pages and lists. The Orbita mouse by Cyber Sport takes a new approach with its continuous scrolling capability, achieved by employing the whole round mouse as a scroll wheel which rotates on a ball bearing base.
Scroll wheels are prevalent on modern computer mice. To many users, they have become an integral part of the hardware interface. However, non-wheeled mice are still available.
Scroll wheels can also be found on such handheld devices as portable digital audio players, PDAs, or mobiles phones such as early Sony models and BlackBerry devices. On the Apple iPod, the scroll wheel uses touch sensitive technologies from Synaptics (instead of being mechanical).
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