Introduction - Java Software Solutions: Foundations of Program Design - page 5

FIGURE 1.2 An example of a graphical user interface (GUI)

for measuring temperature. The alcohol rises in a tube in direct proportion to
the temperature outside the tube. Another example of analog information is an
electronic signal used to represent the vibrations of a sound wave. The signal's
voltage varies in direct proportion to the original sound wave. A stereo amplifier
sends this kind of electronic signal to its speakers, which vibrate to reproduce
the sound. We use the term analog because the signal is directly analogous to the
information it represents. Figure 1.3 graphically depicts a sound wave captured
by a microphone and represented as an electronic signal.
Digital technology breaks information into discrete pieces and represents those
pieces as numbers. The music on a compact disc is stored digitally, as a series of
numbers. Each number represents the voltage level of one specific
instance of the recording. Many of these measurements are taken in
a short period of time, perhaps 44,000 measurements every second.
The number of measurements per second is called the

KEY CONCEPT
Digital computers store information
by breaking it into pieces and repre-
senting each piece as a number.

sampling rate.
If samples are taken often enough, the discrete voltage measurements