Scroll wheel

A scroll wheel (or mouse wheel) is a hard plastic or rubbery disc (the "wheel") on a computer mouse that is perpendicular to the mouse surface. It is normally located between the left and right mouse buttons.

It is used, as the name suggests, for scrolling. It can often also be used as a third mouse button by pressing on it. The wheel is often – but not always – engineered with detents to turn in discrete steps, rather than continuously as an analog axis, to allow the operator to more easily intuit how far they are scrolling.

Some modern mice can scroll vertically, as well as horizontally, using a scroll-wheel (introduced by Microsoft), scroll ball (found, for example, on Apple's Mighty Mouse), pointing stick,touchpad (as on Apple's Magic Mouse), optical sensor, or a second scroll wheel. Logitech mice with 'Free Spinning' scroll wheels use a 14 gram scroll wheel with high rotational inertia like a flywheel that can be used to quickly scroll through long pages and lists. A peculiar early example was a mouse by Saitek which had a joystick-style hatswitch on it.

Scroll wheels are prevalent on modern computer mice and 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 such as PDAs, portable digital audio players such as the original Apple iPod, or mobiles phones such as early Sony models and BlackBerry devices.

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