Transcript IT-101

IT-101
Section 001
Introduction to Information
Technology
Lecture #2
Overview
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Chapter 1:
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The Information age
Information, messages and signals
Information systems
Analog and digital information
Chapter 3:
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Representing information in binary form
The Information Age
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Information technology impacts every
aspect of our lives
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Work: IT industry-has become a major
economic sector
Home: Information appliances, information
utilities
Leisure: audio/video, gaming
Social: Web communities
Financial: on-line trading and banking
And so on…
Benefits of Information Technology
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Increased productivity
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Personal flexibility
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Information flow
Access to information (ex: the Internet)
Access to personnel
Data entry
Virtual workplaces
Recreation
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Gaming
Costs of Information Technology
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Equipment expense
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Social costs
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Equipment obsolescence. Example: personal
computers and CPU’s
Increased unemployment
Job elimination
Reduction in middle management
Personal costs
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Relearn new techniques and technologies
Career obsolescence (ex: typing pools)
Impact of Information Technology in
the last 30 years
1970
1999
Cost of 1 MHz processing
power
Cost of 1 Mbit memory
$7,601
$0.17
$5,257
$0.17
Cost of sending a trillion
bits of information
$150,000 $0.12
Source: The Economist, Sept. 23, 2000
 Information, Messages and
Signals
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From last class, we defined information: Knowledge
communicated or received concerning a particular fact or
circumstance
It is important to distinguish between information, message and
signal
Signal: The actual entity (electrical, mechanical, etc) that is
transmitted from sender to receiver (ex: electrical signals, sound
waves, optical pulses)
Message: The content of the signal (ex: binary representations,
alphanumeric characters, speech etc.)
Information: The content of the message, i.e. the knowledge
that is communicated/received by the message.
As an example, consider the following
scenario:
Information
Message (speech)
Information
Yes, Mr. Faraday would
like to meet you at 4:00
p.m. today
Electrical signal
Sure, I’ll be there!
 Information Systems
Definition:
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information system: 1. A system, whether automated or manual, that
comprises people, machines, and/or methods organized to collect,
process, transmit, and disseminate data that represent user
information. 2. Any communications and/or computer related
equipment or interconnected system or subsystems of equipment that
is used in the acquisition, storage, manipulation, management,
movement, control, display, switching, interchange, transmission, or
reception of voice and/or data, and includes software, firmware, and
hardware. [NIS] 3. The entire infrastructure, organization, personnel,
and components for the collection, processing, storage, transmission,
display, dissemination, and disposition of information. [INFOSEC-99]
Source: telecom glossary (http://atis.org)
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Examples of information systems include:
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The phonograph
The telephone system (communication system)
The Phonograph
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The phonograph, invented by
Thomas Edison in 1877 is a device
that can record sounds and play
them back
A diaphragm, which vibrates when
sound waves are impinged on it, is
connected to a stylus which can cut
grooves in a solid material such as
tin foil, wax, or vinyl. As the stylus is
moved over the material, the
vibration from the diaphragm
produces a groove whose depth is
proportional to the sound intensity
To play back, the stylus travels over
the grooves of the recording, which
vibrates the diaphragm and
produces sound
The Telephone System
Components of Communication
Systems
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Input transducer: The device that converts a physical signal
from the source to an electrical, mechanical or electromagnetic
signal that is more suitable for communicating
Transmitter: The device that sends the transduced signal to the
receiver
Transmission channel: The physical medium through which the
signal is transmitted
Receiver: The device that recovers the transmitted signal from
the channel
Output transducer: The device that converts the received signal
back into a useful physical quantity
Exercise: Identify the above components for the phonograph and
telephone system.
 Analog and Digital
Information
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The term analog is used to refer to the natural world,
where time is continuous, and most parameters (like
light, sound intensity, position, etc. ) can vary
smoothly and continuously over some range, taking
on an infinite number of possible values. Analog
signals have properties of frequency, amplitude and
phase
The term digital is used to refer to information
representations for which both time and the value
being measured move in discrete steps i.e. when
there are a finite number of possible values
Useful article for understanding difference between analog and digital:
http://cgi.sacbee.com/ib/tech/wiredlife/20010621.html
Discrete and Continuous
Representations of Temperature
Digital Information
Analog Information
Examples of Analog and Digital
Information
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Analog:
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Sound waves
Light intensity
Temperature
Digital:
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The number of cars passing through a point on the freeway
per hour
The flight time of a pilot per week
Examples of Analog and Digital
Devices:
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Analog
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Microphone
Cassette player
Radio
Vinyl record player
Photograph camera
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Digital:
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DVD
Digital camera
HDTV
CD player
New cell phones
Fiber-optics
The Natural World is Analog
Human speech is an example of analog communication.
Speech causes air to vibrate with varying amplitude (volume) and frequency (pitch).
This continuous acoustical waveform can be detected by a microphone and converted into an
analogous electrical waveform for transmission over a circuit.
The Computer World is Digital
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Digital computers communicate using 2 discrete values. In other
words, they speak in binary (0 and 1).
Of course, 0s and 1s are not literally transmitted
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In an electrical network, variations in voltage represent one of the
two discrete values.
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In an optical network, pulses of light provide the discrete values.
Recall that the 0s and 1s are the “message” and the pulses of light or
voltage variations are the “signal.”
Two values in different combinations sufficiently encode text, numbers,
image, and video!
Note that the telegraph was an early example of communications
using discrete, electrical pulse transmission.
Digital vs. Analog
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Analog signals are susceptible to distortion and inaccuracy due
to other signals (interference)
Digital information can be compressed for efficient transmission
and storage
Digital information can be encrypted for increased security and
multiplexed for increased capacity
Digital technology is much cheaper
Digital signals can be accurately reproduced
Digital signals are easier to detect
There is opportunity for error detection and correction in digital
technology
Digital vs. Analog (cont..)
If an analog signal provides such a close representation of information
sources, why do we use digital?
Noise
Analog signal
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(unwanted electrical/
electromagnetic energy)
Distorted Signal
Above is shown an analog signal on magnetic tape. Random
fluctuations in the magnetic tape add “noise” to the signal. The tonelike noise components cannot be removed and become part of the
subsequent versions of the analog signal.
Digital vs. Analog (cont..)
Digital Signal
Noise
Distorted Signal
Threshold
Detector
Processor
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Regenerated Digital Signal
Restoration of digital signals stored on magnetic tape. Random
fluctuations in the magnetic tape add noise to the digital signal. A
processor, called a threshold detector, compares the signal to a
threshold (dashed line) and decides that the data value is a 1 if the
signal lies above the threshold, or a 0, otherwise.
 Representing information in
binary form
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In order to efficiently store, transmit, process and retrieve
information, we need a process for encoding the information
The encoding process is a method of representing information
using a finite number of basic elements, called an alphabet
Examples of written alphabets are:
 The English alphabet: 26 lower case, 26 upper case, 10
numbers and 32 special characters=94 characters
 The Chinese alphabet (Mandarin): 40, 000 characters
A comparison between these alphabets shows us that the
Chinese alphabet is a more powerful code as it can convey more
information with a single complex character (symbol). Fewer
characters are required to communicate an idea
However, this code is very complex and the task of
distinguishing one character from the other at the receiving end
is highly challenging
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We therefore would require a more robust scheme since reliable
manipulation of information depends upon resistance to errors
The fewer symbols the code has, the easier it is to distinguish
the symbols from each other
The code with the minimum number of symbols (2) is called the
binary code
It consists of two distinct symbols: 1 and 0
Any information can be coded using only these two symbols
called bits: Binary digits
Why Use a Code with Only Two
Values?
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A binary system is more resistant to errors
The two symbols are highly distinguishable from one another.
Consider a compact laser disc for music or computer storage:
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A CD is comprised of an enormous number of domains, each of
which stores one bit.
Each domain either has a smooth surface that reflects the laser or
a “pit” which doesn’t reflect the laser. It’s very clear which of the
two values is held by each domain.
If, instead of 2 values, each domain held 3 values (domains of zero,
partial, and high reflectivity) a simple fingerprint might create
errors.
The 2 clear values make the system simple and reliable.
Two values correspond well to the “on” and “off” states of
electronic switches that comprise digital computers.
Bits in the physical world
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Generation
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Storage
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Varying the voltage in a circuit
Varying the light intensity (ex: switch light on or off)
Magnetic disk: Magnetized in one of two directions: “up” or
“down”
Compact disc: Constructed to reflect or not reflect light
using a reflective surface or pit
Transmission media
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Wires
Electrical cables
Optical fibers
Air
Comments for next class
Please go over class notes and read chapter 3
 Topics to be covered next class:
Chapter 3:
 Representing Information in Binary Form (cont..)
 Binary to decimal conversion
 Decimal to binary conversion
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