IT101

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IT-101

• Introduction to Information Technology

Lecture 2 Spring 2005
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Overview

• Chapter 1
• Information, messages and signals
• Information systems
• Analog and digital information
• Chapter 3
• Representing information in binary form

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Information, Messages and Signals

• It is important to distinguish between
  information, messages and signals
• 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 song,
  speech, binary code etc.)
• Information The content of the message, i.e. the
  knowledge that is communicated/received by the
  message.
• Message and information are sometimes used
  interchangeably, however there is a subtle
  difference between the two.

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• As an example, consider the following
  scenario

Information
Message (speech)
Information
Yes, Mr. Faraday would like to meet you at 400
p.m. today
Sure, Ill be there!
Electrical signal
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Information Systems

• Information System The entire
  infrastructure, organization, and components that
  collect, process, store, transmit, display,
  disseminate, and act on information
• Source http//www.jfcom.mil/about/glossary.htmI

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Information System Example
The Phonograph

• Breakthrough in the communication of information
  (sound).
• Invented by Thomas Edison.
• A diaphragm vibrates when it detects sound waves.
• The diaphragm transfers a vibration to a stylus,
  which cuts grooves into a solid material.

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Information System Example
The Telephone System
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Information System Example
The World Wide Web
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Components of Communication Systems

• Input Transducer- Also known as a sensor.
  Converts a physical signal to an electrical,
  electromechanical, mechanical, optical, or
  electromagnetic signal.
• Transmitter - A device that sends the transduced
  signal to a receiver.
• Transmission Channel - A physical medium by which
  a signal is carried.
• Receiver - A device that recovers a transmitted
  signal from the transmission channel.
• Output Transducer - A device that converts the
  received signal back into a useful physical
  quantity.

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Analog and Digital Information

• 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
• 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

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Analog Versus Digital
DISCRETE
CONTINUOUS
Discrete Information
Analog Information
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Analog Versus Digital
Exists for ALL values of space and time Variables
can have ALL POSSIBLE values Example smoothly
rotating hand on a clock
Analog Information

• When each discrete information value is converted
  to a binary value, the information becomes
  digitized.

Exists at SPECIFIC POINTS in space and
time Variables can have ONLY SPECIFIC values
Example Clock hand that rotates in jumps
(ticks)
Discrete Information
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Examples of Analog and Digital Devices

• Analog
• Microphone
• Cassette player
• Radio
• Vinyl record player
• Photograph camera

• Digital
• DVD
• Digital camera
• HDTV
• CD player
• Most cell phones
• Fiber-optic systems

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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
analog electrical signal for transmission over a
piece of wire.
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The Computer World is Digital

• 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
• In an electrical network, variations in voltage
  represent one of the two values.
• In an optical network, pulses of light provide
  the discrete values.
• The pulses of light or voltage variations are the
  signal.
• Two values in different combinations sufficiently
  encode text, numbers, image, and sound!
• Recall that the telegraph was an early example of
  communications using discrete, electrical pulse
  transmission.

Digital
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Digital vs. Analog

• 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

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A Problem with Analog
If an analog signal provides such a close
representation of information, why do we use
digital?
Noise
(unwanted electrical/ electromagnetic energy)
Analog signal
Distorted Signal

• Analog signal on magnetic tape. Random
  fluctuations in the magnetic tape add noise to
  the signal. The noise cannot be removed and
  becomes part of the subsequent versions of the
  analog signal.

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The Digital Advantage
Digital Signal
Noise
Distorted Signal
Threshold Detector
Regenerated Digital Signal
Processor

• Restoration of digital signals stored on magnetic
  tape. Random fluctuations in the magnetic tape
  add noise to the digital signal. A device,
  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.

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Representing information in binary form

• 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 characters94
  characters
• The Chinese alphabet (Mandarin) 40, 000
  characters
• 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 onecharacter from the other at
  the receiving end is highly challenging

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Representing information in binary form (cont.)

• We 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 alphabet with the minimum number of symbols
  (2) is called the binary alphabet or code
• It consists of two distinct symbols 1 and 0
• Any information can be coded using only these two
  symbols called bits Binary digits

00110010100101010011101010101001010101010101010101
01010
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Why Use a Code with Only Two Values?

• 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
• 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 light or a pit which doesnt
  reflect the light.
• 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.

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Bits in the physical world

• Generation
• Varying the voltage in a circuit
• Varying the light intensity (ex switch light on
  or off)
• Storage
• Magnetic disk Magnetized in one of two
  directions up or down
• Compact disc Constructed to reflect/not reflect
  light using reflective surfaces and pits
• Transmission
• Electrical wires
• Optical fibers
• Air

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How do Digital Systems Produce 0s and 1s?

• Physically, a 1 or a 0 can be produced in several
  ways
• The presence of or level of voltage in an
  electrical network.
• A pulse of light or varying of light intensity in
  an optical network.
• Discrete variations of signal amplitude in a
  radio network like satellite or cellular.
• STORAGE - To store binary data, storage media
  must represent two values.
• Magnetic disk can be magnetized in two directions
  up or down
• Laser disk domains have either a smooth surface
  or pitted surface.
• TRANSMISSION - Two distinct electrical or optical
  quantities are transmitted such as a pulse of
  light and absence of light.
• PROCESSING - Computer circuits can be broken down
  into the fundamental building block, the
  electronic switch (either on or off).

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Practical Use

• Everyday stuff measured in bits
• 32-bit sound card
• 64-bit video accelerator card
• 128-bit encryption in your browser
• 650 MB CD

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Comments for next class

• Go over todays lecture notes
• Download next weeks lecture notes
• Finish reading chapters 1 and 3