Mouse

Mouse - Most modern computers today are run using a mouse controlled pointer. Generally if the mouse has two buttons the left one is used to select objects and text and the right one is used to access menus. If the mouse has one button (Mac for instance) it controls all the activity and a mouse with a third button can be used by specific software programs.

One type of mouse has a round ball under the bottom of the mouse that rolls and turns two wheels which control the direction of the pointer on the screen. Another type of mouse uses an optical system to track the movement of the mouse. Laptop computers use touch pads, buttons and other devices to control the pointer. Hand helds use a combination of devices to control the pointer, including touch screens.
 
Note: It is important to clean the mouse periodically, particularly if it becomes sluggish. A ball type mouse has a small circular panel that can be opened, allowing you to remove the ball. Lint can be removed carefully with a tooth pick or tweezers and the ball can be washed with mild detergent. A build up will accumulate on the small wheels in the mouse. Use a small instrument or finger nail to scrape it off taking care not to scratch the wheels. Track balls can be cleaned much like a mouse and touch-pad can be wiped with a clean, damp cloth. An optical mouse can accumulate material from the surface that it is in contact with which can be removed with a finger nail or small instrument.


How mouse system works

Sensors are the movement detectors (typically optomechanical) which sense the mouse movement and button swiches which sense the button states. Mouse controller reads the state of those sensors and takes acount of current mouse position. When this information changes the mouse controller sends a packet of data to the computer data interface controller.
The mouse driver in the computer received that data packet and decodes the information from it and does actions based on the information. Typically mouse driver has the information of the current mouse state (position and button states) and tells them to the application or operating when it asks them. Typically the mouse drive calls mouse cursor moving routines when mouse is moved and sends messages to the software when buttons are pressed.

In typical modern PC mouse driver the actual cursor movement is not linearly related to the mouse movement. This might sound a bit strange but it has been found that there are better ways to change the mouse movement to cursor muvement than just simply causing one mouse step to move the cursor one pixel. During the pioneering research done at Apple Computer in the devellopment of the graphical user interface (GUI), it became apparent that no particular ratio between mouse movement and cursor movement was best suited for all tasks.

Early work detected that there are two basic movements in the use of pointing devices: move cursor to desired area and then exactly to desired target. Those two movements have contradictory requirements, so Apple solved the problem by monitoring the mouse movements and change it's CPI (counts per inch) characteristics. When the mouse was moved slowly it remained 100 CPI and when the mouse was moved fast it appears to be 400 CPI mouse. This method of adjusting CPI based on its usage has now been adopted by the default driver in Windows 95 and is now the most commonly accepted way of translating mouse movements to cursor screen movement