Transcript Chapter 2 - Bilal A. Bajwa

Information Technology in Theory
By Pelin Aksoy and Laura DeNardis
Chapter 2
Understanding the Digital Domain
Objectives
• Understand the difference between analog and digital
representations of information
• Learn about techniques for transmitting and storing
digital information
• Understand the use of multipliers for representing,
transmitting, and storing large amounts of digital
information
• Discuss the advantages of representing information in
digital format and using digital devices for
processing, exchanging, and storing information
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Emergence of the Digital Age
• “Digital information” refers to representations of
numbers, text, sound, and images as a combination of
two fundamental logic symbols: 1 and 0
• These symbols are also called binary symbols, binary
digits, or bits
• Digital devices process information in the form of
ones and zeros; in other words, they speak a binary
language
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Emergence of the Digital Age
(continued)
• People recognized the possibilities of digital
technology
• They began to develop digital devices that could
“speak” the binary language advancement
• To realize this, an efficient switch was needed
– Vacuum tube
– Transistor
– Integrated circuit
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Emergence of the Digital Age
(continued)
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Emergence of the Digital Age
(continued)
An integrated circuit
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Emergence of the Digital Age
(continued)
• Moore’s Law states that “The number of devices that
can be integrated on a chip doubles every 18 months”
• Current technology indicates that Moore’s Law will
reach its limit in the future, so research on alternative
technologies is underway
• Digital technology has evolved tremendously over the
past few decades and will continue to evolve
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Analog Information
• Digital devices process many forms of information in
combinations of bits
• Most information we encounter is analog, not in
terms of 1s and 0s
• When we speak, we exchange information in analog
format; what we hear varies proportionally, or
analogously, to the sound produced by the person
who is speaking
• We call this analog information
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Analog Information (continued)
• A speedometer example helps to understand the
difference between analog and digital
• The speed varies continuously and an infinite number
of speed values exist over a given time measurement
• Information produced by the speedometer is analog
information
• The speedometer is classified as an analog device
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Analog Information (continued)
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Analog Information (continued)
• It is desirable to digitize analog information using
analog-to-digital converters
• First task to digitize is to reduce infinite number of
speed measurements to a finite number
• In other terms, make the information discrete
• Reducing infinite number of speed measurements
corresponds to sampling each measurement
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Analog Information (continued)
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Analog Information (continued)
• The next task is to round the speed values to the
closest speed value available
• Finally the rounded-off speed values are assigned a
binary code
• A speedometer that is able to display digital speed
values is classified as a digital device
• Can you name other digital devices?
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Analog Information (continued)
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Analog Information (continued)
• To convert any form of analog information to digital,
the analog information should first be reduced to a
finite set of values
• Each value should be rounded off
• Each rounded-off value should then be assigned an
appropriate binary code
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Manipulating Bits
• Speedometer example conveyed how bits can
logically represent information
• How can bits be physically generated so as to
transmit and store digital information?
• Bits may be physically generated using electrical
energy, magnetic energy, or electromagnetic energy
• A signal is used to transport bits physically across a
transmission medium
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Manipulating Bits (continued)
• Examples of signals include:
–
–
–
–
–
–
Electrical signals
Magnetic signals
Optical signals
Sound signals
Radio frequency signals
Etc.
• Examples of transmission media include metallic
wires, fiber-optic cables (i.e. optical fibers), air, etc.
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Manipulating Bits (continued)
• Bits should always exist physically in a form that is
based on the type of transmission media to be used
• If using fiber-optic cables, bits should be sent out as
optical signals
• If using metallic wires, bits should be sent out as
electrical signals, etc.
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Manipulating Bits (continued)
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Data Rate
• Rate at which bits are sent out over a transmission
medium
• Measured in terms of bits per second (bps) and bit
period in terms of seconds
• Data rate=1/bit period
• More complex version of this expression is explained
in a later chapter
• If bit period is 1 second, then data rate is 1 bps
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Data Rate (continued)
• Large and small numbers are usually expressed more
compactly through the use of multipliers
• Multipliers commonly used in the IT world within the
context of transmission:
– Kilobits per second (Kbps) 103 = 1000 bps (thousand)
– Megabits per second (Mbps) 106 = 1,000,000 bps
(million)
– Gigabits per second (Gbps) 109 = 1,000,000,000 bps
(billion)
– Terabits per second (Tbps) 1012 = 1,000,000,000,000
bps (trillion)
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Data Rate (continued)
• Solve some examples:
– Calculate how many bits per second are transmitted
over a 384-Kbps cable modem connection
– Calculate how many bits per second are transmitted
over a 1.25-Gbps fiber optic connection
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Storing Bits
• Storage media store digital information in some
physical form
• Most forms of storage media traditionally fall into
one of the following categories:
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–
–
–
–
Mechanical storage
Magnetic storage
Optical storage
Magneto-optical storage
Electronic storage
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Storing Bits (continued)
• Examples of current and historical storage media
include:
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–
–
–
–
–
CDs
DVDs
Hard disks
Floppy disks
Flash memory
Punch cards
• Can you identify which media are mechanical,
magnetic, optical, and electronic?
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Mathematics of Storage
• Digital information is stored by grouping bits into
bytes
• 8 bits = 1 byte
• Multipliers are commonly used in the IT world within
the context of storage:
–
–
–
–
Kilobyte (KB) 210 = 1,024 bytes
Megabyte (MB) 220 = 1,048,576 bytes
Gigabyte (GB) 230 = 1,073,741,824 bytes
Terabyte (TB) 240 = 1,099,511,627,776 bytes
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Mathematics of Storage (continued)
• Some examples:
– Calculate the storage capacity (the number of bits)
that can be stored on a 700-MB CD
– Calculate the number of bits in a 68-KB digital file
stored on your hard disk
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Advantages of Digital Technology
•
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•
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Ability for noise removal
Capacity for error control
High speed
High level of security
Amenable to compression
Reliable storage of information
Ease of reproduction
Simplicity in transmission
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Ability for Noise Removal
• Noise is defined as an effect that disrupts a signal,
hence the information carried by the signal
• Noise acts upon both analog and digital signals
• It is desirable to remove noise in its entirety from the
signal
• It is always easier to remove noise from digital
signals than it is from analog signals
• Threshold device may be used to remove noise from
a noisy digital signal
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Ability for Noise Removal (continued)
Noisy analog signal
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Ability for Noise Removal (continued)
Noisy digital signal
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Ability for Noise Removal (continued)
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Capacity for Error Control
• Not all levels of noise may be removed from a noisy
digital signal
• If noise levels are too great, a receiver might make an
incorrect decision on the value of the bit, resulting in
an error
• Special error control schemes may be used to detect
and sometimes correct errors if they occur at the
receiving end of a communications system
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Capacity for Error Control (continued)
• Error control is accomplished by applying extra bits
prior to transmission at the transmitting end
• These redundant bits help the receiver in
detecting/correcting errors if they occur
• Errors are not only limited to transmission systems
• They also frequently arise within storage systems
• Similar error control schemes may be applied prior to
storage so that the reading device may be able to
detect/correct errors
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High Speed
• Digital information may be transmitted and processed
faster than analog information
• Improved transmission media materials and special
transmission techniques enable faster transmission
speeds
• Miniaturization of transistors, the development of
novel materials, and more refined manufacturing
techniques for integrated circuits enable faster
processing
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High Level of Security
• Digital systems can protect sensitive information by
encrypting information
• Encryption ensures that if third parties intercept
information-carrying signals, they cannot decipher
the signals
• One encryption method is to reverse the order of the
bits before transmission; for example, a bit stream of
1100 is transmitted as 0011
• As long as the transmitting and receiving ends agree
on the scheme, the receiver can decipher the
information
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Amenability to Compression
• Digital information is highly amenable to
compression (a reduction in the overall number of
bits to be transmitted/stored)
• This is especially true for digital audio, image, and
video files
• Applying compression algorithms can help to achieve
various levels of compression
• Both lossy and lossless compression schemes exist in
IT
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Reliable Storage of Information
• Analog storage approaches are highly amenable to
degradation during storage
• If an analog audio cassette is played repeatedly, the
overall quality of the audio stored on the cassette is
reduced
• In contrast, digital storage approaches such as CDs
and flash drives can store information more reliably
over long periods of time
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Ease of Reproduction
• Analog information is highly susceptible to
degradation during reproduction
• An analog audio cassette tape copied in a double
cassette recorder usually does not have the same
quality as the original tape
• Information on digital media such as flash drives can
be reproduced with the same quality as the original,
and with greater ease
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Simplicity in Transmission
• Digital information is easy to transmit, because the
transmitter needs to generate a signal with only a
discrete number of values
• Consequently, the receiver needs to follow a signal
with only discrete number of values
• Transmitters that have to transmit analog signals must
be able to generate a signal with an infinite number of
values, and the receiver has to follow this complex
signal
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Summary
• Digital devices are technologies that process
information in the form of 1s and 0s
• Digital information is discrete, comprising a finite
number of information values
• Analog information is continuous, comprising an
infinite number of values
• The transistor and the integrated circuit—a layer of
silicon containing numerous interconnected
transistors—were major breakthroughs that led to
smaller and faster digital technologies
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Summary (continued)
• Moore’s Law states that the number of transistors
contained on an integrated circuit doubles every 18
months
• Any form of information, including sound, text, or
images, can be represented digitally using ones and
zeros
• The bits can be physically generated using various
sources of energy, such as electricity, light, or radio
frequency
• The rate at which bits are transmitted over any medium
is called the data rate
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Summary (continued)
• Bits are usually stored on magnetic media such as
hard disks, on optical media such as CDs and DVDs,
on magneto-optical media such as magneto-optical
drives, and on electronic media such as flash cards
• Digital technology has many advantages over analog
technology, including resistance to noise, higher
speeds, and greater reliability
• Digital technology also offers more efficient security,
error detection and correction, compression, and ease
of reproduction
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