IT-101Section 001 Introduction to Information Technology Lecture #2
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 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: Information Message (speech) Information Yes, Mr. Faraday would like to meet you at 4:00 p.m. today Sure, I’ll be there! Electrical signal
Information Systems Definition: • 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, 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 Phonograph
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 digitalis used to refer to information representations for which both time and the value being measured move in discretesteps 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
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 Information
Analog Microphone Cassette player Radio Vinyl record player Photograph camera Digital: DVD Digital camera HDTV CD player New cell phones Fiber-optics Examples of Analog and Digital Devices:
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 • 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
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..) If an analog signal provides such a close representation of information sources, why do we use digital? Noise • (unwanted electrical/ • electromagnetic energy) Analog signal Distorted Signal • 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.
Digital vs. Analog (cont..) 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 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 • 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