A scroll wheel is a hard plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 or rubber

Rubber

Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

y disc (the "wheel

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

") on a computer mouse that is perpendicular to the mouse surface. It is normally located between the left and right mouse buttons.

Functionality

It is used, as the name suggests, for scrolling

Scrolling

In computer graphics, filmmaking, television production, and other kinetic displays, scrolling is sliding text, images or video across a monitor or display. "Scrolling", as such, does not change the layout of the text or pictures, or but incrementally moves the user's view across what is...

. 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

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

) or a scroll ball

Trackball

A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a cursor...

 (found on Apple

Apple Computer

Apple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...

's Mighty Mouse

Apple Mighty Mouse

The Apple Mouse is a multi-button USB mouse manufactured and sold by Apple Inc. It was announced and sold for the first time on August 2, 2005, and a Bluetooth version was available from 2006 to 2009...

). Logitech

Logitech

Logitech International S.A. is a global provider of personal peripherals for computers and other digital platforms headquartered in Romanel-sur-Morges, Switzerland. The company develops and markets products like peripheral devices for PCs, including keyboards, mice, microphones, game controllers...

 MicroGear mice (like the MX Revolution

Logitech MX Revolution

The Logitech MX Revolution is a wireless laser mouse manufactured by Logitech and released in 2006 in celebration of the company's 25th anniversary. The MX Revolution is the first mouse to feature a free-spinning alloy scroll wheel, which allows continuous scrolling for several seconds with a...

 and the VX Revolution

Logitech VX Revolution

The Logitech VX Revolution is a wireless laser, notebook mouse manufactured by Logitech and released in 2006 in celebration of the company's 25th anniversary. The VX Revolution is the first mouse to feature a free-spinning alloy scroll wheel, which allows continuous scrolling for several seconds...

) use a 14 gram scroll wheel which can preserve the moment of inertia

Moment of inertia

In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...

 like a flywheel

Flywheel

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

 and can be used to quickly scroll through long pages and lists. The Orbita mouse

Orbita mouse

The Orbita mouse, sometimes unofficially nicknamed the round mouse, is a wireless 3-axis rotating mouse. The patented mouse was developed by Australian company Cyber Sport, and was released in January 2009...

 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, PDA

Personal digital assistant

A personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...

s, or mobiles phones such as early Sony

Sony

, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

 models and BlackBerry

BlackBerry

BlackBerry is a line of mobile email and smartphone devices developed and designed by Canadian company Research In Motion since 1999.BlackBerry devices are smartphones, designed to function as personal digital assistants, portable media players, internet browsers, gaming devices, and much more...

 devices. On the Apple iPod

IPod

iPod is a line of portable media players created and marketed by Apple Inc. The product line-up currently consists of the hard drive-based iPod Classic, the touchscreen iPod Touch, the compact iPod Nano, and the ultra-compact iPod Shuffle...

, the scroll wheel uses touch sensitive technologies from Synaptics

Synaptics

Synaptics develops human interface solutions for many major consumer electronics companies, such as Apple Inc., Asus, Acer, Dell, Gateway, HP, HTC, Lenovo, LG, Logitech, Nokia, Samsung, Sony, Sony Ericsson, Toshiba and several others...

 (instead of being mechanical).

History

The scroll wheel was invented at Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 in 1993 by Eric Michelman

Eric Michelman

Eric Michelman is credited with inventing the now commonplace computer input device known as the scroll wheel. Scroll wheels are most often located between the left and right-click buttons on modern computer mice.- History :...

. The first example of a scrolling mouse is the Genius EasyScroll mouse made by Taiwan

Taiwan

Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

ese company KYE Systems in 1995, but it was popularized by the Microsoft IntelliMouse

IntelliMouse

IntelliMouse is a brand of computer mice from Microsoft. The IntelliMouse series is credited with a number of innovations. For example, Microsoft was among the first mouse vendors to introduce a scroll wheel, an optical mouse, and dedicated forward and back buttons on the side of the mouse for...

 in 1996 along with support for the mouse wheel in Microsoft Office 97

Microsoft Office 97

Microsoft Office 97 was a major milestone release of Microsoft Office, which included hundreds of new features and improvements, introduced "Command Bars", a paradigm in which menus and toolbars were made more similar in capability and visual design featured natural language systems and...

. It is notably one of the first additions to the basic two-button mouse design used for PCs

Personal computer

A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

 that became a de facto standard

De facto standard

A de facto standard is a custom, convention, product, or system that has achieved a dominant position by public acceptance or market forces...

. Its popularity increased with the proliferation of the World Wide Web

World Wide Web

The World Wide Web is a system of interlinked hypertext documents accessed via the Internet...

, where efficient mouse-only scrolling is most useful.

In the 21st century, scroll wheels started appearing on keyboards

Computer keyboard

In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...

 as well, particularly on Logitech

Logitech

Logitech International S.A. is a global provider of personal peripherals for computers and other digital platforms headquartered in Romanel-sur-Morges, Switzerland. The company develops and markets products like peripheral devices for PCs, including keyboards, mice, microphones, game controllers...

 and Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 models. It is usually located to the left of the caps lock

Caps lock

Caps lock is a key on many computer keyboards. Pressing it sets an input mode in which typed letters are uppercase by default. The keyboard remains in caps lock mode until the key is pressed again...

 key. The implementation of scroll wheels on laptop computers has generally faded, while touchpad

Touchpad

A touchpad is a pointing device featuring a tactile sensor, a specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. Touch pads are a common feature of laptop computers, and they are also used as a substitute for a mouse where desk...

s are often made with the edges acting to scroll the page (rather than to move the cursor

Cursor (computers)

In computing, a cursor is an indicator used to show the position on a computer monitor or other display device that will respond to input from a text input or pointing device. The flashing text cursor may be referred to as a caret in some cases...

), partly making up for the lack of a scroll wheel. On laptops with multitouch capability, scrolling is usually achieved by touching and dragging two fingers on the touchpad at the same time. Many Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 distributions offer a third method of scrolling using the touchpad, where the user will first activate scroll-mode by pressing in a corner of the pad, and than dragging in a circle around the center of the pad, letting go of the touchpad will switch back to the default mouse-mode.

Other applications

In many applications (e.g. web browsers), holding down the control key

Control key

In computing, a Control key is a modifier key which, when pressed in conjunction with another key, will perform a special operation ; similar to the Shift key, the Control key rarely performs any function when pressed by itself...

 while rolling the scroll wheel causes the text

Plain text

In computing, plain text is the contents of an ordinary sequential file readable as textual material without much processing, usually opposed to formatted text....

 size to increase or decrease, or an image in an image-editing or map-viewing program to zoom

Digital zoom

Digital zoom is a method of decreasing the apparent angle of view of a digital photographic or video image. Digital zoom is accomplished by cropping an image down to a centered area with the same aspect ratio as the original, and usually also interpolating the result back up to the pixel...

 in or out, if such a feature is available.

In many first-person shooter

First-person shooter

First-person shooter is a video game genre that centers the gameplay on gun and projectile weapon-based combat through first-person perspective; i.e., the player experiences the action through the eyes of a protagonist. Generally speaking, the first-person shooter shares common traits with other...

 (FPS) games, the scroll wheel is usually set to change weapons. Because of this some gaming mice, such as Logitech G500

Logitech G500

The Logitech G500 is a corded laser mouse produced by Logitech as part of its G series targeted at the gamer market.The G500 has a slot into which the weight caddy can be inserted. The G500 comes with twelve small weights, six being 4.5g and the remaining six 1.7g...

, implement a locking feature that lets the mouse switch between scrolling in steps (needed for gaming) and continuous scrolling (good for web browsing). The scroll wheel is also sometimes used to control the zoom of scoped weapons and binoculars. FPS games with an emphasis on realism may choose to use the wheel for changing between stances. Since the introduction of tilting scroll-wheels, many FPS games use the left-right motion of the scroll wheel to cause the player to lean left and right. A less common use is to use the mouse wheel to adjust the player's speed of movement.

Real time strategy games use the mouse wheel to change the altitude of the camera. Many RTS games also allow control of the camera with the scroll wheel button held down causing the view to either tilt or pan with mouse movement.