The mouse

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A computer mouse is a pointing device (hand control) that detects two-dimensional motion relative to a surface. This motion is typically translated into the motion of a pointer on a display, which allows a smooth control of the graphical user interface.

The mouse
The mouse has become a major component of the majority of desktop computer systems sold today, and is the little box with the tail connecting it to the machine in our
basic computer system picture (Figure 2.1). It is a small, palm-sized box housing a
weighted ball – as the box is moved over the tabletop, the ball is rolled by the table
and so rotates inside the housing. This rotation is detected by small rollers that are
in contact with the ball, and these adjust the values of potentiometers. If you remove
the ball occasionally to clear dust you may be able to see these rollers. The changing
values of these potentiometers can be directly related to changes in position of the
ball. The potentiometers are aligned in different directions so that they can detect
both horizontal and vertical motion. The relative motion information is passed
to the computer via a wire attached to the box, or in some cases using wireless or
infrared, and moves a pointer on the screen, called the cursor. The whole arrangement tends to look rodent-like, with the box acting as the body and the wire as the
tail; hence the term ‘mouse’. In addition to detecting motion, the mouse has typically
one, two or three buttons on top. These are used to indicate selection or to initiate
action. Single-button mice tend to have similar functionality to multi-button mice,
and achieve this by instituting different operations for a single and a double button
click. A ‘double-click’ is when the button is pressed twice in rapid succession. Multibutton mice tend to allocate one operation to each particular button.
2.3
72 Chapter 2 n The computer
The mouse operates in a planar fashion, moving around the desktop, and is an
indirect input device, since a transformation is required to map from the horizontal
nature of the desktop to the vertical alignment of the screen. Left–right motion is
directly mapped, whilst up–down on the screen is achieved by moving the mouse
away–towards the user. The mouse only provides information on the relative movement of the ball within the housing: it can be physically lifted up from the desktop
and replaced in a different position without moving the cursor. This offers the
advantage that less physical space is required for the mouse, but suffers from being
less intuitive for novice users. Since the mouse sits on the desk, moving it about is
easy and users suffer little arm fatigue, although the indirect nature of the medium
can lead to problems with hand–eye coordination. However, a major advantage of
the mouse is that the cursor itself is small, and it can be easily manipulated without
obscuring the display.
The mouse was developed around 1964 by Douglas C. Engelbart, and a photograph of the first prototype is shown in Figure 2.6. This used two wheels that
slid across the desktop and transmitted x–y coordinates to the computer. The housing was carved in wood, and has been damaged, exposing one of the wheels. The
original design actually offers a few advantages over today’s more sleek versions:
by tilting it so that only one wheel is in contact with the desk, pure vertical or horizontal motion can be obtained. Also, the problem of getting the cursor across the
large screens that are often used today can be solved by flicking your wrist to get
the horizontal wheel spinning. The mouse pointer then races across the screen with
no further effort on your behalf, until you stop it at its destination by dropping the
mouse down onto the desktop.