Everybody knows what a computer mouse looks like: it's that plastic little animal-like device on your desk that keeps you connected with your computer. But we never think about its components, that is what's inside. But the computer mouse has changed its appearance and components a lot in time.

The first computer mouse was built in 1964 by Douglas Engelbart. Until then, the arrow keys on the keyboard were the only way of moving the cursor on a computer screen and they sometimes were pretty difficult to use. Dr. Engelbart invented a small, brick-like mechanism made of wood that had only one button and two metallic wheels that were not very easy to maneuver. Those two wheels detected horizontal and vertical movement and transmitted the electric signal to the cursor on the computer screen. One of Dr. Engelbert's colleagues thought the device with its long cable tail looked something like a mouse, and the name stuck.

By 1973, the wheels of the mouse were replaced by a single, free-rolling ball; and two more buttons (for a total of three) had been added to the top. The development of the personal computer caused an explosion of applications for the device because it was small enough to be used at people's workplaces. Engineers used the computer in their work for drawing and drafting and the mouse proved an indispensable tool, small and easy to work with. Some people tried to make a different version of the mouse called the trackball .It was which is essentially a mouse lying on its back and the user rolled the ball instead of moving the entire unit. This new device was most successful for air traffic controllers, gamers and engineers. In time, the mechanical sensors in the mouse were removed and replaced by optical-electronic sensors. They are more efficient and cheaper than the old mechanical sensors. So the next step in the evolution of the computer mouse was the optical mouse. It did not have any moving parts and the mouse movement was detected by a photo detector that translated it into cursor movements on screen.

Little by little the appearance and components of the computer mouse changed again. The wheels that were placed first below the mouse were replaced by a single ball, then by a scroll on top of the mouse; then the cordless or wireless mouse was invented by using radio-frequency signals borrowed from garage door openers or infrared signals adapted from remote controls. Now the mouse has a laser beam that detects movement and transmits it on the screen

The mouse's shell is the outer, hard plastic body that the user moves across a flat surface. Then there's the cord that connects the mouse to the computer or, in the case of wireless mice the wireless transmitter. At the tail end we can find the buttons -the external contacts to small electrical switches from one button at the beginning to even 18 buttons (I saw this in a recent magazine and I couldn't believe my eyes). When you press a button you close the switch with a click. It works due to electricity that closes the circuit and allows the computer to receive the command.

The plastic rubber ball that you see only half under the mouse in fixed in a plastic hatch. Inside, the ball is held in place by a support wheel and two shafts. When we move the mouse the ball rolls on the surface of your desk and one shaft turns with horizontal motion and the second responds to vertical motion. The two shafts have a spoked wheel at their end and this wheel also turns when they move. A LED sends infrared light signals through the spokes and they are intercepted by a light detector - this is the case of the optical mouse. The dark and light are translated by photo transistors into electrical pulses that go to the interface in the mouse and these pulses make the cursor move accordingly on the screen.

The skeleton of the internal part of the mouse is the printed circuit board on which all the internal parts of a mouse are fixed, including the interface integrated circuit. This is also knows as the computer chip and it collects the information from the switches and the signals from the photo transistors and sends a data stream to the computer.

In order for the mouse to work properly and interact with your computer, it must have a driver installed, that varies according to your type of mouse. This is considered to be the external brain of the computer that allows it to understand the mouse's signals. The driver tells the computer how to interpret all the data sent by the mouse, including speed, direction, and clicked commands. In some cases this driver lets you assign certain commands to every mouse button or adjust the resolution of the mouse. Some companies sell computer packages and in this case you can see that the drivers are built in.

Almost all the parts of a computer mouse are made of ABS, a plastic that is injection-molded. The metallic core of the ball is coated in a special rubber. The electrical micro-switches are made of plastic and metal. The integrated circuits or chips are standard items but they may differ from one supplier to another.

Each company that produces computer mice has its own design and thus they have to adjust the shape of the printed circuit board according to this design. It is a flat, resin-coated sheet. The smaller elements that we can find inside a mouse are: electrical resistors, capacitors, oscillators, integrated circuits and other components and they are made of various types of metal, plastic, and silicon.

The development of the computer mouse was done together with internet development. This resulted in some changes of the mouse in order to suit web surfing: the scroll wheel inserted between the two buttons that allows the user to surf the web pages faster. Furthermore the user has the opportunity to programme the mouse buttons to perform Internet functions. They can move back or forward between web pages, return to the home page or any other internet related command you might think of. I even saw a foot mouse with pedals that replaced the ball and buttons; you can move the cursor with one and click with the other.

I have noticed a constant preoccupation for ergonomic models of mice lately; they even introduced the touchpad as a method of avoiding wrist or hand injury. But I think this is not the end. The computer mouse will follow the evolution of the Internet and most likely will suffer significant changes to respond to this challenge.