Lecture #2

IT-101Section 001

Introduction to Information Technology

Overview

Chapter 1: The Information age Information, messages and signals Information systems Analog and digital information

Chapter 3: Representing information in binary

form

The Information Age Information technology impacts

every aspect of our lives 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 Increased productivity

Information flow Access to information (ex: the Internet) Access to personnel Data entry

Personal flexibility Virtual workplaces

Recreation Gaming

Costs of Information Technology Equipment expense

Equipment obsolescence. Example: personal computers and CPU’s

Social costs Increased unemployment Job elimination Reduction in middle management

Personal costs 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

$7,601 $0.17

Cost of 1 Mbit memory $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 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:

Yes, Mr. Faraday would like to meet you

at 4:00 p.m. today Sure, I’ll be there!

Electrical signal

Message (speech) Information Information

Information SystemsDefinition: 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)

Examples of information systems include: The phonograph The telephone system (communication system)

The Phonograph 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

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 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

Analog: Sound waves Light intensity Temperature

Digital: 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:

Analog Microphone Cassette player Radio Vinyl record

player Photograph

camera

Digital: DVD Digital camera HDTV CD player New cell phones Fiber-optics

The Natural World is Analog

This continuous acoustical waveform can be detected by a microphone and converted into an analogous electrical waveform for transmission over a circuit.

Human speech is an example of analog communication.Speech causes air to vibrate with varying amplitude (volume) and frequency (pitch).

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 discrete values.

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

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..)

Analog signal

Noise

If an analog signal provides such a close representation of If an analog signal provides such a close representation of information sources, why do we use digital?information sources, why do we use digital?

Above is shown an analog signal on magnetic tape. Random fluctuations in the magnetic tape add “noise” to the signal. The tone-like noise components cannot be removed and become part of the subsequent versions of the analog signal.

Distorted Signal(unwanted electrical/electromagnetic energy)

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.

Digital Signal Noise Distorted Signal

ThresholdDetector

Regenerated Digital SignalProcessor

Digital vs. Analog (cont..)

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 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

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? 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 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

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 or not reflect light

using a reflective surface or pit Transmission media

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