THE MOUSE

In the early 1980s, a keyboard would probably have been the only input device that came with a computer. Today, all new PCs come with some kind of pointing device as standard equipment. If the computer is a desktop or tower model, the pointing device is usually a mouse. A mouse is an input device that rolls around on a flat surface (usually on a desk or mouse pad) and controls the pointer. The pointer is as on screen object, usually an arrow, that is used to select text, access menus, move files, or interact with other program files.

The mouse first gained recognition when it was packaged with the Apple Macintosh computer in 1984. Initially, some users scoffed at this simple device, but it quickly became apparent that the mouse is very convenient for entering certain types of input. For example, a mouse lets you position the cursor anywhere on the screen quickly and easily without having to use the cursor movement keys. You simply move the pointer to the on screen position you want, press the mouse button, and the cursor appears there. A mouse also allows you to create graphic elements on the screen, such as lines, curves, and freehand shapes, and it makes using menus and interactive message boxes easier. With this new capability, the mouse helped establish the computer as a versatile tool for graphic designers, starting what has since become a revolution in that field.

Using the Mouse

You use a mouse to point to a location on the screen. Push the mouse forward, and the pointer goes up; move the mouse to the left, and the pointers goes to the left. To point to an object or location on the screen, you simply use the mouse to place the pointer on tope of the object or location.

Everything you do with a mouse you accomplish by combining pointing with four other techniques: clicking, double-clicking, dragging, and right-clicking. Clicking, double-clicking and dragging. To click on something with the mouse means to move the pointer to the item on the screen and to press and release the mouse button once. To double-click on an item means to point to it with the cursor and to press and release the mouse button twice in rapid succession. To drag an item, you position the mouse cursor over the item, then depress the mouse button and hold it down as you move the mouse.

Although most mice have two buttons, clicking, double-clicking, and dragging are usually carried out with the left mouse button. The mouse usually sits to the right of the keyboard (for right-handed people) and the user maneuvers the mouse with the right hand, pressing the left button with the right forefinger, as shown in Figure 3.5. For this reason, the left mouse button is sometimes called the primary mouse button.

If you are left-handed, you may want to use the operating system to set the right mouse button as the primary button. This lets you place the mouse to the left of the keyboard, control the mouse with your left hand, and use your left forefinger for most mouse actions.

Although the primary mouse button is used for most muse actions, an increasing number of programs also use the right mouse button. Windows 95, or example, uses the right mouse button extensively to open shortcut menus. Using the right mouse button is known as right-clicking.

The Inner Workings of a Mouse

A mouse is really a simple device. The most common type of mouse has a ball inside it that extends just below the housing. When you slide the mouse around on a flat surface, such as a desktop or a mouse pad, the ball rolls as a result of friction. On two sides of the ball, at a 90-degree angle from each other, are two small rollers that touch the mouse and spin when the ball rolls. A sensor detects how much each roller spins and sends this information to the computer. The computer translates the information and changes the position of the on screen pointer to correspond to the position indicated by the mouse.

Like the keyboard, a mouse does not actually send a message directly to the program that the computer is running. Rather, it sends an interrupt request to the CPU. The program that is running checks regularly to see whether the mouse has been used; if it has, the program reads a memory location to see what happened, then reacts appropriately.

Click below to goto the Interrupt and IRQ section

Although most mouse units are connected directly to computers with a cord, some are not. A cordless mouse communicated with a special controller in or near the computer by transmitting a low-intensity radio or infrared signal. Cordless mice are more expensive that their tailed cousins, but many people like the freedom of movement they allow without the restriction of a cord.

Another difference between mice is the way in which they sense movement. Most track the rotation of rollers, but a few track movement optically by sensing the movement of dots or a grid on the mousepad. These optional models are generally more expensive. They are also less versatile, because they can be used only on their own special pads. Their chief advantage is that they are highly sensitive and therefore more accurate than standard mice. These "special" mice are basically used by drafters and architects.

The Trackball

A trackball s a pointing device that works like an upside-down mouse. You rest your thumb on the exposed ball and your fingers on the buttons. To move the cursor around the screen, you roll the ball with your thumb. Because you do not move the hole device, a trackball requires less space than a mouse, so when space is limited, a trackball can be at the advantage. Trackballs gained popularity with the advent of laptop computers, which typically are used on laps or on small work surfaces without room for a mouse. Some trackballs, are not even attached to the computer and act like a remote control for the pointer. They are especially useful when giving presentations, because the presenter often walks around the room rather than sitting at a computer.

The Trackpad

The trackpad is a stationary pointing device that many people find less tiring to use than a mouse or trackball. The movement of a finger across a small touch surface is translated into cursor movement on the computer screen. The touch-sensitive surface may be just 1.5 – 2 inches square, so the finger never has to move far. The size also makes it well suited for a notebook computer. The advantage to a trackpad is that there are no moving parts. This allows maintanence free use of the device nd will rovide for a longer life.

Pointers in the Keyboard

Several companies now offer another space-saving pointer device, consisting of a small "eraser-head" positioned near the middle of the keyboard, typically between the "g" and "h" keys. The eraser-head is controlled with either forefinger. Two buttons that perform the same function as mouse buttons are just beneath the spacebar and are pressed with the thumb. Because it occupies so little space, the device is built into several laptop models. Another advantage is that users do not have to take their hands off the keyboard, so the device saves time and effort.

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