That little device .  .  .  glued to your hand, 8 to 14 hours a day  .  .  .  the lowly little mouse.  There are several types of mice on the market -  track-ball, optical, and wireless.  The traditional "track-ball" is going the way of the dinosaur, but many people still own a track-ball today, so we will cover it.

Track-Ball Mouse

As you move the mouse, a hard rubber ball, called a "track ball", in the bottom of the mouse rolls along, and two cylindrical rollers in the X and Y direction (horizontal and vertical)  move inside the mouse.  The X and Y roller movements cause digital electrical signals to be sent to the motherboard of your PC, to let it know what direction and how far to move the mouse pointer on the screen.  In addition, signals are sent when you click on any of the mouse buttons, to let the computer know to select or move items.

Underneath the mouse, the end of the rollers have round wafers with small holes cutout.  On one side of the holes is an infrared light, and on the other side a sensor (see image below).  As the wafer spins, flashes of light hit the sensor, and bytes of info which represent the quantity and speed of movement, are fed into the PC through the mouse cable.

Mice connect to PCs in one of two ways: 

• Serial mice (rare) connect directly to a 9-pin RS-232C serial port, or if they have an adapter, they can be connected to a PS/2 port. This is the simplest type of connection.  The problem with serial Mice is that they use one of the 15 valuable "interrupts" that a computer needs to be able to communicate with all of it's devices.  Serial mice are practically phased out at this point, but they still exist on older PC's
• PS/2 mice connect to a PS/2 port, whic is a small round port with Pins, similar to the port your keyboard plugs into (and actually sits right next to the keyboard port) 

PS/2 Mouse connector - pin1 is at 7'oclock

Counting from Pin1, clockwise :

Pin1 -   Unused
Pin2 -   +5 volts (to power the chip and LEDs)
Pin3 -   Unused
Pin4 -   Clock
Pin5 -   Ground
Pin6 -   Data

No one knows this - but whenever the mouse moves or the user clicks a button, the mouse sends three bytes of data to the computer. The first byte's 8 bits contain:  

Bytes two and three contain the X and Y movement values respectively. These two bytes contain the number of pulses that have been detected in the X and Y direction since the last packet was sent.  The data is sent from the mouse to the computer serially on the data line, with the clock line pulsing to tell the computer where each bit starts and stops. 11 bits are sent for each byte (1 start bit, 8 data bits, 1 parity bit and 1 stop bit). The PS/2 mouse sends on the order of 1,200 bits per second. That allows it to report mouse position to the computer at a maximum rate of about 40 reports per second. If you are moving the mouse very rapidly, the mouse may travel an inch or more in 1/40th of a second. This is why there is a byte allocated for X and Y motion in the data protocol.

Optical Mouse

This type of mouse, originally called the "IntelliEye" by Microsoft, has no track-ball - which means no more cleaning hassles - YES !!.  Instead, it sends laser light out, which is reflected back to a sensor, which calculates the movement.  So far the problem with this mouse is that it is a bit heavy, and takes getting used to, since you frequently need to lift a mouse to move it to the other side of the pad.  I am sure that this is the future of mice, since cleaning the rollers is quite a hassle.

Microsoft IntelliEye

Wireless Mouse

These are cordless mice which aren't physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer.  The earlier models of these went through batteries within several days.  But now they last for months, which makes them a viable alternative.  Still, most people prefer the optical mouse, with a wire for power.  That way you never have to worry about running out of batteries.  Also, does the wire really bother people all that much?  Of course not.   

Cleaning a Track-Ball Mouse - the only maintenance a mouse has (and it can be very trying at times) - is that the rollers next to the track ball become dirty and require cleaning.  To clean a mouse, you must turn it over and unscrew the round plate, which hold to track ball in place.  Generally, all that is required is one quarter of a turn :

At this point you will see three rollers, all of which tend to get dirty fairly quickly - a couple of weeks to a month, depending on amount of usage.  The X and Y rollers are the ones that send the movement signals to your PC.  The tension roller is juts a passive, spring-loaded roller, but it is important, because it insures that the track ball maintains contact with the X and Y rollers (it actually pushes the track-ball up against the other two rollers).  Therefore, all three rollers must be clean :

Notice the small rings of dirt and grease on both of the signal rollers.  The position of the dirt, in keeping with Murphy's law, will always - ALWAYS - be right at the point where the track ball contacts the roller.  There are several ways to clean these rollers, but none are easy.  I have heard of using a toothbrush, but have not tried it.

The rollers are down and inside the mouse cavity and are hard to get at.  Also, the dirt is typically a hardened ring, and even when you soften the ring with solvent, and try to rub it left and right, it simply slides left and right.  

If the ring appears to be rock-hard, take a pair of scissors or a small knife, and "gently" scrape sideways to try and break the ring.  If it breaks and falls down into the cavity, then turn the mouse right-side up and vigorously shake it until the ring of dirt drops out.  I rarely use this method because the ring usually is stubborn and has hair and fibers in it - and as stated it has a tendency to simply slide left and right.  It would seem fine to slide it all the way to the end and leave it, but it works it's way back into the center later, or gums up the bearings of the roller.

Typically, I take a piece of a napkin, spray some Windex on it, and then in a circular motion, rub it on the ring.  Make sure to rotate the rollers with the napkin so that you liberally wet down the ring of dirt.  Wait 15 seconds and wet it down again, and then continue the circular motion in a more vigorous manner. Continue until done. 9 times out of ten the ring will soften and dislodge itself.  1 time out of ten I have to get is as soft as possible, and the use the edge of a pair of scissors to break a section of it.

Mouse Pads - the pad surface is quite important - it needs to stay clean so as not to foul your Mouse.  In addition, it needs to have some absorbency so as to absorb the grease and oils from your hand so that the track-ball stays cleaner.  There is one type of mouse pad to stay away from - those beautiful shiny ones with pictures.  They are so shiny that the trackball can slip while you move the mouse - and also the do not absorb grease and oil well.