This is a copy of an essay/article I’ve just written for Computing, at college:

Mice have now become something we take for granted when using a computer; however it took a long time for them to be widely adopted. Given that people naturally point at things — usually before they speak — it is surprising that it took so long for a good pointing device to develop. The idea of a “mouse” was originally developed in the 60’s, however a real, working mouse was not developed until much later on.

When computers were originally developed, they did not have a graphical user interface. They often operated on command lines, just requiring text input. It was a long time before even arrow keys were implemented.

Light pens were used on a variety of machines as a pointing device for many years. These worked by attaching an LED to a pointing device, and were picked up by the CRT monitor via the refreshing of the screen. Although these were novel at the time, they did not feel natural to use, and were not very widely adopted.

The first time the mouse was seen was when it was attached to an original Apple Mac. It was a revolutionary idea at the time, and it was accepted as very natural to use. However, MS DOS (the primary operating system on the PC) did not support a mouse, and so it was not widely adopted. When the first GUI version of Windows was released (Windows 3.1), the mouse was taken on board to a much larger degree, and was included with almost all computers.

The main goal of any mouse is to convert the motion of your hand into signals (often in binary) that the computer can use. in general, this is achieved through using five different components:

1. A ball inside the body of the mouse comes into contact with the desk, and rolls as the mouse is moved across the surface it is on.

   

2. There are two different “rollers” situated above the ball inside the mouse, and as the ball moves around, these spin as well. There are two rollers to ensure that the mouse’s movement in either the up/down (Y) or side to side (X) actions are translated. Both rollers often move at the same time.
   
3. The rollers each connect to a shaft, and the shaft spins a disk with many small holes.
   
4. Around each edge of the disc, there two components. One is an infrared LED, emitting a constant beam of infrared light. The other is an infrared receiver, detecting the beam. As the mouse moves, the disc spins, and the beam of light is broken and re-made many times a second. From this motion, the mouse can calculate the distance and speed the mouse is moving.
   
5. The mouse has a processor built onto its electronic circuits, which can take signals from both of the rotating discs, and also the two (or more) mouse buttons on the top-front of the device. This processor can convert the signals it receives into binary data, which can be transmitted to the computer either through a USB or PS/2 mouse cord/connection. The computer can then interpret this input, and perform the necessary calculations to convert the data to cursor movement across the screen.

As time has moved on, an alternative to the original ball mouse has appeared. This is an optical mouse, which reads the surface it is travelling across with an LED rather than through mechanical parts.

The optical mouse actually uses a tiny camera to take 1,500 pictures every second. The LED hits the surface or worktop, and takes a precise image of the patterns and textures on the surface of that material. Because so many pictures are taken, in such a short period of time, the mouse can compare one with another, and perform calculations to see how far (if at all) the mouse has moved since the last photo.

This allows a set of coordinates to be calculated, which can be sent to the computer in order to convert the physical movement of the mouse into software to move the cursor across the screen.

Optical mice have several benefits over wheeled mice:

• There are no moving parts, which reduces the chance of a mechanical failure in the device
• Dirt and grit cannot enter past the ball, which could affect the rollers and disc in the ball mouse
• Because so many images are taken per second, a very smooth action is gained
• It works on almost any surface

Although USB is coming into use more and more, many mice in use today still use the PS/2 connector. This is a brief explanation of how the PS/2 connector works:

The pins around the PS2 connector have the following functions. (Pin 1 is the one directly to the lower left of the black square in the middle)

1. Unused
2. +5 volts (to power the chip and LEDs)
3. Unused
4. Clock
5. Ground
6. Data