Mouse

The mouse refers to a piece of external hardware for user input, or a Human Interface Device (HID).
It typically consists of a sensor, two buttons and a scroll wheel.
They are available in both wired and wireless forms and there is a great variety of mice in the market.
The name 'mouse' came from the appearance of early mice, which had the cord attached to the rear, which made them look like mice.
==Technologies==
===Mechanical mice===
Early mice were 'mechanical', or 'ball mice'. It used a ball that could rotate in any direction (it would do so when the user moved it across a surface) and light sensors inside would detect the motion of the ball, which would then be fed as input information to the host computer.
These quickly became the dominant form of input with personal computers throughout the 1980s to 1990s.
===Optical mice===
Optical mice use a LED and photodiodes to detect motion relevant to the surface it is moving on, rather then moving internal parts (as with mechanical mice).
===Modern optical mice===
Modern surface-independent optical mice work by using an optoelectronic sensor to take successive pictures of the surface on which the mouse operates. As computing power grew cheaper, it became possible to embed more powerful special-purpose image-processing chips in the mouse itself. This advance enabled the mouse to detect relative motion on a wide variety of surfaces, translating the movement of the mouse into the movement of the pointer and eliminating the need for a special mouse-pad. This advance paved the way for widespread adoption of optical mice. Optical mice illuminate the surface that they track over, using an LED or a laser diode. Changes between one frame and the next are processed by the image processing part of the chip and translated into movement on the two axes using an optical flow estimation algorithm. For example, the Avago Technologies ADNS-2610 optical mouse sensor processes 1512 frames per second: each frame consisting of a rectangular array of 18×18 pixels, and each pixel can sense 64 different levels of gray.
====Infrared mice====
These are functionally similar to typical optical mice, but use an infrared emitter instead. These are typically far more accurate and save power. However, one cannot look directly at the sensor in order to avoid potential eye damage.
Infrared mice make up a percentage of high end mice, such as the Razer Death Adder which uses a third generation infrared sensor, capable of tracking 1800dpi.
====Laser mice====
The laser mouse uses an infrared laser diode instead of an LED to illuminate the surface beneath their sensor. As early as 1998, Sun Microsystems provided a laser mouse with their Sun SPARCstation servers and workstations. However, laser mice did not enter the mainstream market until 2004, when Logitech, in partnership with Agilent Technologies, introduced its MX 1000 laser mouse. This mouse uses a small infrared laser instead of an LED and has significantly increased the resolution of the image taken by the mouse. The laser enables around 20 times more surface tracking power to the surface features used for navigation compared to conventional optical mice, via interference effects. While the implementation of a laser slightly increases sensitivity and resolution, the main advantage comes from power usage.
Lasers are typically used in high end mice, such as the Logitech G9. Lasers are typically far more sensitive then optical mice, with the typical laser mouse being capable of 2,000dpi. High end gaming mice like the aforementioned G9 and Razer's Lachesis command a 4,000dpi sensor.
====Sensor color====
The color of the optical mouse's light-emitting diodes varies with each model. Red was the most common, as red diodes were the cheapest when optical mice first arrived on the market. Today, a wide array of colors exist, such as blue or green. Some models' diodes even change color, cycling through colors of the rainbow for instance. Red, however, is still the most common.
====Power Saving====
Most modern mice (particularly wireless mice) have a power saving function.
This occurs by blinking or dimming the LED or laser, when the mouse is left alone for a certain period which varies by mouse.
This is intended to save power and prolong battery life, particularly with wireless models.
Gaming mice frequently forego this implementation as the 'waking up' of the sensor typically induces latency and reduces responsivness, which is not preferrable.
===Optical versus Mechanical===
Unlike mechanical mice, which can become clogged with lint, optical mice have no rolling parts; therefore, they do not require maintenance other than removing debris that might collect under the light emitter. However, they generally cannot track on glossy and transparent surfaces, including some mouse-pads, sometimes causing the cursor to drift unpredictably during operation. Mice with less image-processing power also have problems tracking fast movement, though high-end mice can track at 2 m/s (80 inches per second) and faster.
Some models of laser mice can track on glossy and transparent surfaces, and have a much higher sensitivity than either their mechanical or optical counterparts. Such models of laser mice cost more than LED based or mechanical mice.
As of 2006, mechanical mice have lower average power demands than their optical counterparts. This typically has no practical impact for users of cabled mice (except possibly those used with battery-powered computers, such as notebook models), but has an impact on battery-powered wireless models.
Optical models will outperform mechanical mice on uneven, slick, soft, sticky, or loose surfaces, and generally in mobile situations lacking mouse pads. Because optical mice render movement based on an image which the LED (or infared diode) illuminates, use with multi-colored mouse pads may result in unreliable performance; however, laser mice do not suffer these problems and will track on such surfaces. The advent of affordable high-speed, low-resolution cameras and the integrated logic in optical mice provides an ideal laboratory for experimentation on next-generation input-devices. Experimenters can obtain low-cost components simply by taking apart a working mouse and changing the optics or by writing new software.
===Interfaces===
Most lower end mice typically use the PS/2 interface, while most modern models utilise a free USB port.
Gaming mice almost always use USB, due to the enhanced data rate provided by the USB bus. This also allows them to report more frequently and be more responsive.
==Buttons==
The common mouse now has three buttons, one left and one right, with the scroll wheel being clickable.
====Additional buttons====
Modern mice manufacturers have been adding extra buttons to their mice for a long time. For some, these buttons can have a hardwired function (the most common one being a magnifier). But most of the more expensive models enable the end-user to bind a function or a keyboard key to that button, through the drivers. This is most frequently seen in gaming mice, where some users tend to prefer to be able to control some things with the mouse - such as binding the reload key to an additional button on the mouse.
Most typically, there are two extra buttons on the left side of the mouse, although there are also some with seven - like the Razer Diamondback which has two extra buttons on each side, making a total of seven. The extra buttons can also be placed just behind the scroll wheel.