The Digital Signal
All data that a computer processes must be encoded digitally,
as a series of zeroes and ones. Internally, computers are
digital because they consist of discrete units called bits
that are either on or off. But by combining many bits in
complex ways, computers simulate analog events. (Analog
is a term for information being used in its original form).
An input device such as a phone set takes an acoustic signal
(which is a natural analog signal) and converts it into
an electrical equivalent in terms of volume (signal amplitude)
and pitch (frequency of wave change). Since the telephone
company’s signaling is already set up for this analog
wave transmission, it's easier for it to use that as the
way to get information back and forth between your telephone
and the telephone company
Because analog transmission only uses a small portion of
the available amount of information that could be transmitted
over copper wires, the maximum amount of data that you can
receive using ordinary modems is about 56 Kbps (thousands
of bits per second) as bits and bytes stored in electronic
memory, similar to facts stored in a person's mind.
Distinct pieces of information are usually formatted in
a special way. All software is divided into two general
categories: data and programs. Programs are collections
of instructions for manipulating data. Data can exist in
a variety of forms -- as numbers or text on pieces of paper.
The term data is often used to distinguish binary machine-readable
information from textual human-readable information. For
example, some applications make a distinction between data
files (files that contain binary data) and text files (files
that contain ASCI data). In database management systems,
data files are the files that store the database information,
whereas other files, such as index files and data dictionaries,
store administrative information, known as metadata.
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