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
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 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
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