texte inginerie din curs
TRANSCRIPT
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Television
Video
Computers
How Computers Work
ScannersElectronics
Electronic devices and components
Electromechanics
Environment
Power Stations
Optical Fiber Communication
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Television
Television is a telecommunication system for broadcasting and receiving moving
pictures and sound over a distance. The term has come to refer to all the aspects of television
from the television set to the programming and transmission.
The word is derived from mixed Latin and Greek roots, meaning "far seeing" (Greek "tele," meaning far, and Latin "visus," meaning seeing.
The origins of what would become today!s television system can be traced back as far as
the discovery of the photoconductivity of the element selenium by illoughby #mith in $%&',
and the invention of a scanning disk by aul )ipkow in $%%*. +ll practical television systems
use the fundamental idea of scanning an image to produce a time series signal representation.
That representation is then transmitted to a device to reverse the scanning process. The final
device, the television, relies on the human eye to integrate the result into a coherent image.
The first modern television broadcasts were made in ngland in $-'. Television did
not become common in /nited #tates homes until the middle $-01s. hile )orth +merican
over2the2air broadcasting was originally free of direct marginal cost to the consumer and
broadcasters were compensated primarily by receipt of advertising revenue, increasingly/nited #tates television consumers obtain their programming by subscription to cable
television systems or direct2to2home satellite transmissions. 3n the /nited 4ingdom, on the
other hand, the owner of each television must pay a license fee annually which is used to
support the 5ritish 5roadcasting 6orporation.
The elements of a simple television system are7
+n image source 2 this may be a camera for live pick2up of images or a flying spot
scanner for transmission of films.
+ sound source.
+ transmitter, which modulates one or more television signals with both picture and
sound information for transmission.
+ receiver (television which recovers the picture and sound signals from the television
broadcast.
+ display device turns the electrical signals into visible light and audible sound.
ractical television systems include e8uipment for selecting different image sources,
mixing images from several sources at once, insertion of pre2recorded video signals,
synchroni9ing signals from many sources, and direct image generation by computer for such
purposes as station identification. Transmission may be over the air from land2based
transmitters, over metal or optical cables, or by radio from synchronous satellites. :igital
systems may be inserted anywhere in the chain to provide better image transmission 8uality,
reduction in transmission bandwidth, special effects, or security of transmission from theft by
non2subscribers.
Readin and vocabular!"
$. hat is Television;
<. hat is the origin of the word television;
'. hich is the fundamental idea that television systems use;
*. here and when were the first broadcasts made;
0. hich are the elements of the television systems;
. =ow may the transmission be done;
&. hy is television so important;#ook up and $ind the meanin o$ the words"
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telecommunication
broadcasting
transmission
photoconductivity
scanningadvertising
satellite
receiver
display
bandwidth
subscriber
to modulate
%atch the words or the e&pressions with their de$initions"
$. adapter a. a part that electrically or physically connects a device to acomputer or to another device
<. ampere (+ b. a high2temperature conditioning of magnetic material to
relieve stresses introduces when the material was formed
'. analog device c. a microcircuit in which the output is a mathematical function
of the input
*. anneal d. a device that is the beginning point for getting radio, T> or
similar signals, for the final point for transmitting them
0. antenna e. the robot state in which automatic operations can be initiated
. application f. to run the robot by executing a program
&. automatic mode g. a program or group of programs that perform given task? asmaller form of an application is an applet
%. automatic robot
run
h. a unit used to define the rate of flow of electricity (current
in a circuit? units are one coulomb (,<%x$1$% electronics per
second
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Video
Video is the technology of capturing, recording, processing, transmitting,
and reconstructing moving pictures, typically using celluloid film, electronic
signals, or digital media, primarily for viewing on television or computer monitors.
The term video (from the Latin for "3 see" commonly refers to several
storage formats for moving pictures7 digital video formats, including :>:,
@uickTime, and AG2*? and analog videotapes, including >=# and 5etamax.
>ideo can be recorded and transmitted in various physical media7 in celluloid
film when recorded by mechanical cameras, in +L or )T#6 electric signals
when recorded by video cameras or in AG2* or :> digital media when
recorded by digital cameras.
'ualit! of video essentially depends on the capturing method and storageused. :igital television (:T> is a relatively recent format with higher 8uality
than earlier television formats and has become a standard for television video.
()*video, digital video in three dimensions, premiered at the end of <1th
century. #ix or eight cameras with real2time depth measurement are typically
used to capture ':2video streams. The format of ':2video is fixed in AG2*
art $ +nimation Bramework eCtension (+BC.
3n the /4, +ustralia, and )ew Dealand, the term video is often used
informally to refer to both video recorders and video cassettes? the meaning is
normally clear from the context.
Frame rate, the number of still pictures per unit of time of video, ranges
from six or eight frames per second (fps for old mechanical cameras to $<1 or
more frames per second for new professional cameras. +L (urope, +sia,
+ustralia, etc. and #6+A (Brance, Eussia, parts of +frica etc. standards
specify <0 fps, while )T#6 (/#+, 6anada, Fapan, etc. specifies <-.-& fps. Bilm
is shot at the slower frame rate of <*fps. To achieve the illusion of a moving
image, the minimum frame rate is about ten frames per second.
Video can be interlaced or progressive. 3nterlacing was invented as a way
to achieve good visual 8uality within the limitations of a narrow bandwidth. The
hori9ontal scan lines of each interlaced frame are numbered consecutively and partitioned into two fields7 the odd field consisting of the odd2numbered lines
and the even field consisting of the even2numbered lines. )T#6, +L and
#6+A are interlaced formats. +bbreviated video resolution specifications
often include an I” to indicate interlacing. Bor example, +L video format is
often specified as 0&i01, where 0& indicates the hori9ontal resolution, I H
indicates interlacing, and 01 indicate 01 (single2field frames per second.
Readin and vocabular!"
$. hat is the video technology;
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<. hat is the origin of the term video;
'. hat does this term refer to;
*. hen did ':2videos first appear;
0. hat does the term video refer to in +ustralia, /4 and )ew Dealand;
. hat is the frame rate;&. hat does the abbreviation 3H indicate;
%. hy is the video technology so important;
#ook up and $ind the meanin o$ the words"
capture
record
process
transmit
reconstruct
moving picture
celluloid film
electronic signal
digital media
view
storage
framework
frame rate
interlacing progressive
%ake sentences usin the $ollowin words"
capturing
recording
processing
transmitting
reconstructingmoving pictures
celluloid film
electronic signals
digital media
viewing
storage
resolution
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%atch the words or the e&pressions with their de$initions"
$. backbone a. a set of nods and their interconnecting links that form a
central, high2speed network interconnecting other,
typically lower2speed, networks or client nodes
<. backup b. abbreviation for binary digitH, it is the smallest piece
of computer information, either the number 1 or $
'. back2up
(of data
c. a term used in video monitor technology to modify how
much voltage is sent to the display area of the monitor or
screen, making the background and foreground images
lighter or darker
*. bit d. important procedure of saving data on a separate data
storage device to prevent complete data loss in case of
unexpected failure of main storage system
0. brightness e. a hard plastic tube, having an inside diameter several
times that of a fiber, that holds one or more fibres
. broadcast f. a transmitted fre8uency signal for radio, television or
similar communications
&. buffer tube g. a system, device, file or facility that can be used as an
alternative in case of a malfunction or loss of data
%. bug
h. a problem with computer software that causes it to
malfunction or crash
-. bus i. % bits of data, the basic measurement of the amount of
data
$1. byte I. a bus is a communication path between different
components in a computer? a bus is typically composed of
address wires, data wires and control wires. Bor example,
a computer!s central processing unit (6/ and memory
are usually connected via a bus
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Computers
+ computer is a machine for manipulating data according to a list of
instructions known as a program.
6omputers are extremely versatile. 3n fact, they are universal information2 processing machines. + computer with a certain minimum threshold capability is
in principle capable of performing the tasks of any other computer, from those of
a personal digital assistant to a supercomputer, as long as time and memory
capacity are not considerations. Therefore, the same computer designs may be
adapted for tasks ranging from processing company payrolls to controlling
unmanned spaceflights. :ue to technological advancement, modern electronic
computers are exponentially more capable than those of preceding generations.
6omputers take numerous physical forms. arly electronic computers were
the si9e of a large room, and such enormous computing facilities still exist for speciali9ed scientific computation J supercomputers J and for the transaction
processing re8uirements of large companies, generally called mainframes.
#maller computers for individual use, called personal computers, and their
portable e8uivalent, the laptop computer, are ubi8uitous information2processing
and communication tools and are perhaps what most non2experts think of as "a
computer". =owever, the most common form of computer in use today is the
embedded computer, small computers used to control another device. mbedded
computers control machines from fighter aircraft to digital cameras.
Kriginally, the term computerH referred to a person who performed
numerical calculations, often with the aid of a mechanical calculating device or
analog computer. xamples of these early devices, the ancestors of the
computer, included the abacus and the +ntikythera mechanism, an ancient Greek
device for calculating the movements of planets, dating from about %& 56. The
end of the Aiddle +ges saw a reinvigoration of uropean mathematics and
engineering, and ilhelm #chickard!s $<' device was the first of a number of
uropean engineers to construct a mechanical calculator. The abacus has been
noted as being an early computer, as it was like a calculator in the past.
3n $%1$, Foseph Aarie Fac8uard made an improvement to existing loom
designs that used a series of punched paper cards as a program to weave intricate patterns. The resulting Fac8uard loom is not considered a true computer but it
was an important step in the development of modern digital computers.
6harles 5abbage was the first to conceptuali9e and design a fully
programmable computer as early as $%<1, but due to a combination of the limits
of the technology of the time, limited finance, and an inability to resist tinkering
with his design, the device was never actually constructed in his lifetime. +
number of technologies that would later prove useful in computing, such as the
punch card and the vacuum tube had appeared by the end of the $-th century,
and large2scale automated data processing using punch cards was performed bytabulating machines designed by =ermann =ollerith.
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:uring the first half of the <1th century, many scientific computing needs
were met by increasingly sophisticated, special2purpose analog computers,
which used a direct mechanical or electrical model of the problem as a basis for
computation. These became increasingly rare after the development of the
programmable digital computer.+ succession of steadily more powerful and flexible computing devices
were constructed in the $-'1s and $-*1s, gradually adding the key features of
modern computers, such as the use of digital electronics and more flexible
programmability. :efining one point along this road as "the first digital
electronic computer" is exceedingly difficult. )otable achievements include the
+tanasoff25erry 6omputer ($-'&, a special2purpose machine that used valve2
driven (vacuum tube computation, binary numbers, and regenerative memory?
the secret 5ritish 6olossus computer ($-**, which had limited programmability
but demonstrated that a device using thousands of valves could be made reliable
and reprogrammed electronically? the =arvard Aark 3, a large2scale
electromechanical computer with limited programmability ($-**? the decimal2
based +merican )3+6 ($-* which was the first general purpose
electronic computer, but originally had an inflexible architecture that meant
reprogramming it essentially re8uired it to be rewired? and 4onrad Duse!s D
machines, with the electromechanical D' ($-*$ being the first working machine
featuring automatic binary arithmetic and feasible programmability.
The team who developed )3+6, recogni9ing its flaws, came up with a far
more flexible and elegant design, which has become known as the >on
)eumann architecture (or "stored program architecture". This stored programarchitecture became the basis for virtually all modern computers. + number of
proIects to develop computers based on the stored program architecture
commenced in the mid to late2$-*1s? the first of these were completed in
5ritain.
>alve2(tube driven computer designs were in use throughout the $-01s,
but were eventually replaced with transistor2based computers, which were
smaller, faster, cheaper, and much more reliable, thus allowing them to be
commercially produced, in the $-1s. 5y the $-&1s, the adoption of integrated
circuit technology had enabled computers to be produced at a low enough costto allow individuals to own a personal computer.
Readin and vocabular!"
$. hat is a computer;
<. hat does the term computerH originally referred to;
'. Give examples of early devices, the ancestors of the computer.
*. hat was )3+6;
0. ho was the first to conceptuali9e and design a fully programmablecomputer;
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. hat replaced the transistor2based computers;
&. hy are computers so important;
#ook up and $ind the meanin o$ the words"
manipulating
versatile
threshold capability
payrolls
unmanned
mainframes
ubi8uitous
embedded
punched
to weave
intricate
patterns
to conceptuali9e
tinkering
tabulating
%atch the words or e&pressions with their de$initions"
$. 6AK#
(6omplementary
Aetal Kxide
#emiconductor
a. a memory chip witch keeps a data record of the
components installed in a computer. The 6AK# uses
the power of a small battery and retains data even
when computer is turned off. 6AK# is used by a
computer to store 6!s configuration settings, such as
date, time, boot se8uence, drive(s parameters etc.
<. conductivity b. a collection of similar information stored in a file,
such a database or addresses, with a given structure for
accepting, sorting and providing, on demand, data for
multiple users
'. conductors c. any piece of control hardware such as an
emergency2stop button, selector switch, control
pendant, relay, solenoid value, sensor etc
*. conductor d. the computing term for information
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0. data e. materials that allow electrical charges to flow
through them
. database f. a measure of the ease with which electrical carriers
flow in a material7 the reciprocal of resistivity
&. decibel g. a software module that hides the details of a
particular peripheral and provides a high2level
programming interface to it
%. decimal h. refers to a base ten number system using the
characters 1 through - to represent values
-. device i. anything that allows the passage of electrons? a
material or obIect through which electricity can flow
with little resistance
$1. device driver I. information indicating the nature or location of a
malfunction
$$. diagnostic k. a standard logarithmic unit for the ratio of two
powers, voltage or currents? in fiber optics the ratio is power
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How computers work hile the technologies used in computers have changed dramatically since
the first electronic, general2purpose computers of the $-*1s, most still use the
stored program architecture. The design made the universal computer a practical
reality.The architecture describes a computer with $our main sections7 the
arithmetic and logic unit (+L/, the control circuitry, the memory, and the input
and output devices (3MK. These parts are interconnected by bundles of wires and
are usually driven by a timer or clock (although other events could drive the
control circuitry.
6onceptually, a computer!s memory can be viewed as a list of cells. ach
cell has a numbered addressH and can store a small, fixed amount of
information. This information can either be an instruction, telling the computer
what to do, or data, the information which the computer is to process using theinstructions that have been placed in the memory. 3n principle, any cell can be
used to store either instructions or data.
The +#, is in many senses the heart of the computer. 3t is capable of
performing two classes of basic operations. The first is arithmetic operations? for
instance, adding or subtracting two numbers together. The set of arithmetic
operations may be very limited? indeed, some designs do not directly support
multiplication and division operations. The second class of +L/ operations
involves comparison operations7 given two numbers, determining if they are
e8ual, or if not e8ual which is larger.
The -.O systems are the means by which the computer receives information
from the outside world, and reports its results back to that world. Kn a typical
personal computer, input devices include obIects like the keyboard and mouse,
and output devices include computer monitors, printers and the like, but as will
be discussed later a huge variety of devices can be connected to a computer and
serve as 3MK devices.
The control system ties this all together. 3ts Iob is to read instructions and
data from memory or the 3MK devices, decode the instructions, providing the
+L/ with the correct inputs according to the instructions, tellH the +L/ what
operation to perform on those inputs, and send the results back to the memory or to the 3MK devices. Kne key component of the control system is a counter that
keeps track of what the address of the current instruction is? typically, this is
incremented each time an instruction is executed, unless the instruction itself
indicates that the next instruction should be at some other location (allowing the
computer to repeatedly execute the same instructions.
#ince the $-%1s the +L/ and control unit (collectively called a central
processing unit or 6/ have typically been located on a single integrated
circuit called a microprocessor.
The functioning of such a computer is in principle 8uite straightforward.Typically, on each clock cycle, the computer fetches instructions and data from
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its memory. The instructions are executed, the results are stored, and the next
instruction is fetched. This procedure repeats until a halt instruction is
encountered.
The set of instructions interpreted by the control unit, and executed by the
+L/, are limited in number, precisely defined, and very simple operations.5roadly, they fit into one or more of four categories7
$ moving data from one location to another?
< executing arithmetic and logical processes on data?
' testing the condition of data?
* altering the se8uence of operations.
3nstructions, like data, are represented within the computer as binary code
a base two system of counting. The particular instruction set that a specific
computer supports is known as that computer!s machine language. /sing an
already2popular machine language makes it much easier to run existing software
on a new machine? conse8uently, in markets where commercial software
availability is important suppliers have converged on one or a very small
number of distinct machine languages.
Larger computers, such as some minicomputers, mainframe computers,
servers, differ from the model above in one significant aspect? rather than one
6/ they often have a number of them. #upercomputers often have highly
unusual architectures significantly different from the basic stored2program
architecture, sometimes featuring thousands of 6/s, but such designs tend to
be useful only for speciali9ed tasks.
Readin and vocabular!"
$ hich are the four main sections of a computer;
< hat is +L/;
' hat is 3MK;
* =ow can the computer!s memory be viewed;
0 hich are the input devices;
hich are the output devices;
& hat is the microprocessor;
#ook up and $ind the meanin o$ the words"circuitry
input device
output device
subtracting
multiplication
division
straightforward
broadly
alteringavailability
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%atch the words or e&pressions with their de$initions"
$. dial2up a. a type of communication that is established by a
switched2circuit connection using the telephone
network
<. dielectric b. messages sent electronically between networked
computers that may be across the office or around the
world
'. e2mail c. the signal or signals received from a controlled
machine or process to denote its response to the
command signal? a signal which is transferred from
the output back to the input for use in a closed2loop
system
*. fax d. a system designed to prevent unauthori9ed access
to or from a private network? all messages entering or
leaving the intranet pass through system, which
examines each message and blocks those that do not
meet the specified security criteria
0. feedback e. non2conductor of electricity? the ability of a
material to resist the flow of an electric current
. firewall f. short for Bacsimile, a fax is a scanned document
that is sent over phone lines to a fax machine or
computer with fax capabilities
&. firmware g. is called so because the entire sections of the
microchip are erased at once or flashed. Blash
memory cards lose power when they are disconnected
(removed from 6, yet the data stored in it is
retained for indefinitely long time until it is rewritten
%. flash memory
(card
h. a flexible magnetic media with a typical capacity
of $.** A5
-. floppy disk i. permanent set of instructions and data programmed
directly into the circuitry of read2only memory for
controlling the operation of the computer or disk
drive.
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Scanners
+ scanner is a device that can read text or illustrations printed on paper and translate the
information into a form the computer can use. + scanner works by digiti9ing an image 2
dividing it into a grid of boxes and representing each box with either a 9ero or a one,
depending on whether the box is filled in. Bor colour and grey scaling, the same principleapplies, but each box is then represented by up to <* bits. The resulting matrix of bits, called a
bit map, can then be stored in a file, displayed on a screen, and manipulated by programs.
Kptical scanners do not distinguish text from illustrations? they represent all images as bit
maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an
optical scanner, you need an optical character reconition (K6E system to translate the
image into +#633 characters. Aost optical scanners sold today come with K6E packages.
Scanners differ from one another in the following respects7
2 scanning technology7 most scanners use chare*coupled device (66: arrays, which
consist of tightly packed rows of light receptors that can detect variations in light intensity and
fre8uency. The 8uality of the 66: array is probably the single most important factor affecting
the 8uality of the scanner. 3ndustry2strength drum scanners use a different technology thatrelies on a photomultiplier tube (AT, but this type of scanner is much more expensive
than the more common 66:2based scanners.
2 resolution7 the denser the bit map, the higher the resolution. Typically, scanners
support resolutions of from &< to 11 dpi.
2 bit depth7 the number of bits used to represent each pixel. The greater the bit depth, the
more colours or greyscales can be represented. Bor example, a <*2bit colour scanner can
represent < to the <*th power ($.& million colours. )ote, however, that a large colour range
is useless if the 66: arrays are capable of detecting only a small number of distinct colours.
2 si9e and shape7 some scanners are small hand2held devices that you move across the
paper. These hand*held scanners are often called half2page scanners because they can only
scan < to 0 inches at a time. =and2held scanners are ade8uate for small pictures and photos,
but they are difficult to use if you need to scan an entire page of text or graphics.
#arer scanners include machines into which you can feed sheets of paper. These are
called sheet*$ed scanners. #heet2fed scanners are excellent for loose sheets of paper, but they
are unable to handle bound documents.
+ second type of large scanner, called a $latbed scanner, is like a photocopy machine. 3t
consists of a board on which you lay books, maga9ines, and other documents that you want to
scan.
Overhead scanners (also called copy board scanners look somewhat like overhead
proIectors. Nou place documents face2up on a scanning bed, and a small overhead tower
moves across the page.
Readin and vocabular!"
$. hat is a scanner;
<. hat is a bit map;
'. hat does the abbreviation K6E refer to;
*. =ow do #canners differ from one another;
0. hat is a charge2coupled device;
. hat does the abbreviation AT refer to;
&. =ow many types of scanners does the text refer to;
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#ook up and $ind the meanin o$ the words"
digiti9ing
to distinguish
photomultiplier tube
resolutiongreyscales
hand2held
sheet2fed
flatbed scanner
overhead scanner
%atch the words or the e&pressions with their de$initions"
$. G#A a. abbreviation for Global #ystem for Aobile communications
<. hard disk b. a data error that does not go away with type (unlike the soft
error and is usually caused by defects in the physical structure
of the disk
'. hard error c. a device used to transfer heat from one substance to another?
can be air to air, air to li8uid, or almost any combination
*. hardware d. acoustical waves with fre8uency content below the fre8uency
of the human ear, typically below <1 =9? can often be felt, or
sensed as a vibration and can induce motion sickness and other
disturbances, and even kill
0. heat exchanger e. is a type of light wave? people cannot see it because it is Iust
outside the range of light which human eyes can detect
. infra2red f. the physical elements and interfaces that constitute a
component or system
&. infrasound g. storage medium that stores data in form of magnetic patterns
on a rigid disk. Aodern hard disks are usually made of several
thin films deposited on both sides of the aluminium, glass etc.
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Electronics
The field of electronics is the study and use of systems that operate by
controlling the flow of electrons (or other charge carriers in devices such as
thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the field of electronics
engineering, and includes the hardware design side of computer engineering.
The study of new semiconductor devices and their technology is sometimes
considered as a branch of physics. This page focuses on engineering aspects of
electronics.
lectronic systems are used to perform a wide variety of tasks. The main
uses of electronic circuits are the controlling, processing and distribution of
information, and the conversion and distribution of electric power. 5oth of these
uses involve the creation or detection of electromagnetic fields and electriccurrents. hile electrical energy had been used for some time to transmit data
over telegraphs and telephones, the development of electronics truly began in
earnest with the advent of radio.
Kne way of looking at an electronic system is to divide it into the following
parts7
2 3nputs J lectronic or mechanical sensors (or transducers, which take
signals from outside sources such as antennae or networks, (or signals which
represent values of temperature, pressure, etc. from the physical world and
convert them into currentMvoltage or digital signals.
2 #ignal processing circuits J These consist of electronic components
connected together to manipulate, interpret and transform the signals. Eecently,
complex processing has been accomplished with the use of :igital #ignal
rocessors.
Kutputs J +ctuators or other devices such as transducers that transform
currentMvoltage signals back into useful physical form.
Kne example is a television set. 3ts input is a broadcast signal received by
an antenna or fed in through a cable. #ignal processing circuits inside the
television extract the brightness, colour and sound information from this signal.
The output devices are a cathode ray tube that converts electronic signals into avisible image on a screen and magnet driven audio speakers.
Readin and vocabular!"
$. hat is the field of electronics;
<. hat devices does the field of electronics use;
'. hich are the main uses of electronic circuits;
*. hat do these uses involve;
0. :ivide the electronic system.
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. hat do electronic or mechanical sensors do;
&. hat do signal processing circuits do;
#ook up and $ind the meanin o$ the words"
thermionic
valves
semiconductors
conversion
transducers
to accomplish
actuator
%atch the words or the e&pressions with their de$initions"
$. 3 a. abbreviation for 3nternet rotocol
<. 3# b. the fastest way to get from one area of an 3nternet
service to another? also used by search engines to find
what one is searching for
'. keyboard c. a light source producing, through simulated emission,
coherent, near monochromatic light
*. keyword d. on most computers, is the primary text input device
0. laser e. current flowing from input or output to case of an
isolated converter at a specific voltage level
. leakage f. abbreviation for 3nternet #ervice rovider
Electronic devices and components
+n electronic component is any indivisible electronic building block
packaged in a discrete form with two or more connecting leads or metallic pads.
6omponents are intended to be connected together, usually by soldering to a
printed circuit board, to create an electronic circuit with a particular function
(for example an amplifier, radio receiver, or oscillator. 6omponents may be
packaged singly (resistor, capacitor, transistor, diode etc. or in more or lesscomplex groups as integrated circuits (operational amplifier, resistor array, logic
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gate etc. +ctive components are sometimes called devices rather than
components.
Aost analog electronic appliances, such as radio receivers, are constructed
from combinations of a few types of basic circuits. +nalog circuits use a
continuous range of voltage as opposed to discrete levels as in digital circuits.The number of different analogue circuits so far devised is huge, especially
because a circuitH can be defined as anything from a single component, to
systems containing thousands of components.
+nalo circuits are sometimes called linear circuits although many non
linear effects are used in analog circuits such as mixers, modulators etc. Good
examples of analog circuits are valve or transistor amplifiers, operational
amplifiers and oscillators.
#ome analog circuitry these days may use digital or even microprocessor
techni8ues to improve upon the basic performance of the circuit. This type of
circuits is usually called Hmixed signalH.
#ometimes it may be difficult to differentiate between analogue and digital
circuits as they have elements of both linear and non linear operation. +n
example is the comparator that takes in a continuous range of voltage but puts
out only one of two levels as in a digital circuit. #imilarly, a transistor amplifier
overdriven can take on the characteristics of a controlled switch having
substantially only two levels of output.
)iital circuits are electric circuits based on a number of discrete voltage
levels. :igital circuits are the most common mechanical representation of
5oolean algebra and are the basis of all digital computers. To most engineers,the terms digital circuitH, digital systemH and logicH are interchangeable in
the context of digital circuits. 3n most cases the number of different states of a
node is two, represented by two voltage levels labelled LowH and =ighH.
Kften LowH will be near 9ero volts and =ighH will be at a higher level
depending on the supply voltage in use.
6omputers, electronic clocks, and programmable logic controllers (used to
control industrial processes are constructed of digital circuits? :igital #ignal
rocessors are another example.
%i&ed*sinal circuits refers to integrated circuits (36s which have bothanalog circuits and digital circuits combined on a single semiconductor die or on
the same circuit board. Aixed2signal circuits are becoming increasingly
common. Aixed circuits contain both analogue and digital components. +nalog
to digital converters and digital to analogue converters are the primary
examples. Kther examples are transmission gates and buffers.
Readin and vocabular!"
$. hat is an electronic component;<. =ow may the components be packaged;
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'. hat is an analog circuit; =ow is it called;
*. hat may an analog circuitry use to improve the performance of the
circuit;
0. hat is a digital circuit;
. hat do LowH and =ighH mean;&. hat 3 a mixed2signal circuit;
#ook up and $ind the meanin o$ the words"
soldering
appliance
overdrive
interchangeable
transmission gate
buffer
analog circuit
digital circuit
mixed2signal circuit
%atch the words or the e&pressions with their de$initions"
$. microchip a. the brain of a robot
<. microphone b. the 6 board of a computer that contains the bus
lines and edge connectors to accommodate other
boards in the system
'.microprocessor c. another term for a computer display screen
*. monitor d. a pointing device that looks like a small box
with a ball underneath it and a cable attaching it to
the computer
0. motherboard e. a unit of measurement e8ual to one billionth of a
meter? e8ual to $12- meter or $12 mm or $12'
micrometer or $1 angstrom
. mouse f. the application of science to develop new
materials and processes by manipulating molecular
and atomic particles
&. nanometer g. converts sound waves to electrical signal
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%.nanotechnology h. a set of computers linked one to another for
resources and data sharing
-. network i. the mode in which a network control programcan direct a communication controller to perform
such activities as pooling, device addressing,
dialling and answering
$1. network
architecture
I. a compact element of a computer central
processing unit, constructed as a single integrated
unit and increasingly used as a control unit for
robots
$$. network
control mode
k. the logical structure and operating principles
(related to services, functions and protocols of a
computer network
Electromechanics
3n engineering, electromechanics combines the sciences of
electromagnetism of electrical engineering and mechanics. Aechatronics is thediscipline of engineering that combines mechanics, electronics and information
technology.
lectromechanical devices are those that combine electrical and mechanical
parts. These include electric motors and mechanical devices powered by them,
such as calculators and adding machines, switches, solenoids, relays, crossbar
switches and stepping switches.
arly on, /repeatersH originated with telegraphy and were
electromechanical devices used to regenerate telegraph signals. The telephony
crossbar switch is an electromechanical device for switching telephone calls.
They were first widely installed in the $-01s in both the /nited #tates and
ngland, and from there 8uickly spread to the rest of the world. They replaced
earlier designs like the #trowger switch in larger installations. )ikola Tesla, one
of the great engineers, pioneered the field of electromechanics.
aul )ipkow proposed and patented the first electromechanical television
system in $%%0. lectrical typewriters developed, up to the $-%1s, as power2
assisted typewritersH. They contained a single electrical component in them, the
motor.
+t 5ell Labs, in the $-*1s, the 5ell Aodel > computer was developed. 3t
was an electromechanical relay2based monster with cycle times in seconds. 3n$-% Garrett #ystems were invited to produce a digital computer to compete
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with electromechanical systems then under development for the main flight
control computer in the /# )avy!s new B2$* Tomcat fighter.
Today, though, common items which would have used electromechanical
devices for control, today use, less expensive and more effectively, a standard
integrated circuit (containing a few million transistors and write a computer program to carry out the same task through logic. Transistors have replaced
almost all electromechanical devices, are used in most simple feedback control
systems, and appear in huge numbers in everything from traffic lights to
washing machines.
Readin and vocabular!"
$. hat is lectromechanics;
<. hat is Aechatronics;
'. hat are electromechanical devices;
*. hat are repeatersH;
0. hen the telephony crossbar switch was first installed;
. =ow were the electrical typewriters;
&. hich devices replaced the electromechanical devices;
#ook up and $ind the meanin o$ the words"
electromechanicsmechatronics
electromagnetism
switches
solenoids
relays
crossbar switches
stepping switches
typewriter
%atch the words or the e&pressions with their de$initions"
$. overcurrent a. any current in excess of a rated current of a drive to
maintain or move to a new position at a given velocity
and acceleration and deceleration rate
<. overhead b. the condition where more load is applied to the
transducer that can measure? this will result in
saturation
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'. overload c. a hand2held computer
*. palm d. a variable that is given a constant value for a
specified application and that may denote theapplication
0. panel e. extra processing time re8uired prior to the execution
of a command or extra space re8uired for non2data
information such as location and timing? disk overhead
occupies up to ten percent of drive capacity
. parameter f. for computer or network security, a specific string of
characters entered by a user and authenticated by thesystem in determining the user!s privileges J if any J to
access and manipulate the data and operations of the
system
&. password g. a line or a list of items waiting to be processed
%. 8ueue h. a formatted display of information that appears on a
display screen
Environment
+n environment is a complex of surrounding circumstances, conditions, or
influences in which a thing is situated or is developed, or in which a person or
organism lives, modifying and determining its life or character.
3n biology, ecology, and environmental science, an environment is the
complex of physical, chemical, and biotic factors that surround and act upon an
organism or ecosystem. The natural environment is such an environment that is
relatively unaffected by human activity.
Environmentalism is a concern that deals with the preservation of the
natural environment, especially from human pollution, and the ethics and
politics associated with this.
3n social science, environmentalism is the theory that the general and
social environment is the primary influence on the development of a person or
group. #ee also nature versus nurture.
+nother social science concept is the Social environment, also known as
milieu.
3n computing, an environment is the overall system, software, or interface
in which a program runs, such as a runtime environment or environment
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variable, or through which a user operates the system, such as an integrated
development environment in which the user develops software or a desktop
environment.
3n art, an environment is a kind of installation, an artwork that surrounds
the observer, and sometimes allows the audience to modify it or interact with it.The first environment was probably the installation of wool strings and playing
children by Aarcel :uchamp in a group exhibition around $-*0.
Readin and vocabular!"
$. hat is an environment;
<. hat is an environment in biology, ecology, and environmental science;
'. hat is an environment in computing;
*. hat is an environment in art;
0. hat is a milieu;
. hat is nvironmentalism;
&. hat is nvironmentalism in social science;
%. =ow important do you think it is to preserve the natural environment;
#ook up and $ind the meanin o$ the words"
deforestation
landfillwaste disposal
overfertili9ation
unleaded petrol M gas
packaging
endangered
global warming
)o tipping
dumping
%atch the words or the e&pressions with their de$initions"
$. @ueue a. + line or a list of items waiting to be processed
<. E+A (Eandom
+ccess Aemory
b. 3s a section of memory that is permanent and will
not be lost when the computer is turned off? the
computer!s start2up instructions are stored
'. EKA (EeadKnly Aemory
c. The command given to execute a program or instruction
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*. Eun d. +bbreviation for Eandom +ccess Aemory? the
working memory of the computer into which
application programs can be loaded and executed
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Power stations
+ power station or power plant is a facility for the generation of electric
power. ower plantH is also used to refer to the engine in ships, aircraft and
other large vehicles. #ome prefer to use the term energy centre because it moreaccurately describes what the plants do, which is the conversion of other forms
of energy, like chemical energy, into electrical energy. =owever, power plant is
the most common term in the /.#., while elsewhere power station and power
plant are both widely used, power station prevailing in the 6ommonwealth and
especially in 5ritain.
+t the centre of nearly all power stations is a generator, a rotating machine
that converts mechanical energy into electrical energy by creating relative
motion between a magnetic field and a conductor. The energy source harnessed
to turn the generator varies widely. 3t depends chiefly on what fuels are easilyavailable and the types of technology that the power company has access to.
Thermal power stations
3n thermal power stations, mechanical power is produced by a heat engine,
which transforms thermal energy, often from combustion of a fuel, into
rotational energy. Aost thermal power plants produce steam, and these are
sometimes called steam power plants. )ot all thermal energy can be transformed
to mechanical power, according to the second law of thermodynamics.
Therefore, thermal power plants also produce low2temperature heat. 3f no use is
found for the heat, it is lost to the environment. 3f reIect heat is employed as
useful heat, for industrial processes or district heating, the power plant is
referred to as a cogeneration power plant or 6= (combined heat2and2power
plant. 3n countries where district heating is common, there are dedicated heat
plants called heat2only boiler stations. +n important class of power stations in
the Aiddle ast uses by2product heat for desalination of water.
Classi$ication
Thermal power plants are classified by the type of fuel and the type of
prime mover installed.
0! $uel
1uclear power plants use a nuclear reactor!s heat to operate a steamturbine generator.
Fossil $uel powered plants may also use a steam turbine generator or in
the case of )atural gas fired plants may use a combustion turbine.
2eothermal power plants use steam extracted from hot underground
rocks.
Renewable ener! plants may be fuelled by waste from sugar cane,
municipal solid waste, landfill methane, or other forms of biomass.
3n integrated steel mills, blast furnace exhaust gas is a low2cost, although
low2energy2density, fuel.
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aste heat from industrial processes is occasionally concentrated enough
to use for power generation, usually in a steam boiler and turbine.0! prime mover
Steam turbine plants use the pressure generated by expanding steam to
turn the blades of a turbine.2as turbine plants use the heat from gases to directly operate the turbine.
)atural2gas fuelled turbine plants can start rapidly and so are used to supply
peakH energy during periods of high demand, though at higher cost than base2
loaded plants.
Combined c!cle plants have both a gas turbine fired by natural gas, and a
steam boiler and steam turbine which use the exhaust gas from the gas turbine to
produce electricity. This greatly increases the overall efficiency of the plant, and
most new base load power plants are combined cycle plants fired by natural gas.
3nternal combustion Eeciprocating engines are used to provide power for
isolated communities and are fre8uently used for small cogeneration plants.
=ospitals, office buildings, industrial plants, and other critical facilities also use
them to provide backup power in case of a power outage. These are usually
fuelled by diesel oil, heavy oil, natural gas and landfill gas.
Aicro turbines, #tirling engine and internal combustion reciprocating
engines are low cost solutions for using opportunity fuels, such as landfill gas,
digester gas from water treatment plants and waste gas from oil production.
Coolin towers and waste heat
5ecause of the fundamental limits to thermodynamic efficiency of any heat
engine, all thermal power plants produce waste heat as a by2product of theuseful electrical energy produced. )atural draft wet cooling towers at nuclear
power plants and at some large thermal power plants are large hyperbolic
chimney2like structures (as seen in the image at the left that release the waste
heat to the ambient atmosphere by the evaporation of water (lower left image.
=owever, the mechanical induced2draft or forced2draft wet cooling towers
(as seen in the image to the right in many large thermal power plants, petroleum
refineries, petrochemical plants, geothermal, biomass and waste to energy plants
use fans to provide air movement upward through down coming water and are
not hyperbolic chimney2like structures. The induced or forced2draft coolingtowers are rectangular, box2like structures filled with a material that enhances
the contacting of the up flowing air and the down flowing water.
3n desert areas a dry cooling tower or radiator may be necessary, since the
cost of make2up water for evaporative cooling would be prohibitive. These have
lower efficiency and higher energy consumption in fans than a wet, evaporative
cooling tower.
here it is economically and environmentally possible, electric companies
prefer to use cooling water from the ocean, or a lake or river, or a cooling pond,
instead of a cooling tower. This type of cooling can save the cost of a coolingtower and may have lower energy costs for pumping cooling water through the
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plant!s heat exchangers. =owever, the waste heat can cause the temperature of
the water to rise detectably. ower plants using natural bodies of water for
cooling must be designed to prevent intake of organisms into the cooling cycle.
+ further environmental impact would be organisms that adapt to the warmer
temperature of water when the plant is operating that may be inIured if the plantshuts down in cold weather.
Readin and vocabular!"
$. hat is a power station or a power plant;
<. =ow is mechanical power produced in thermal power stations;
'. hich is the classification of thermal power plants;
*. hat is a nuclear power plant;
0. hat is a fossil fuel powered plant;
. hat is a geothermal power plant;
&. hat is a renewable energy plant;
%. hat do steam turbine plants use;
-. hat about gas turbine plants and combined cycle plants;
$1.hy are power plants so important for the industry;
#ook up and $ind the meanin o$ the words and the e&pressions"
commonwealth
harnesscogeneration
desalination
reciprocating engines
forced2draft cooling towers
induced2draft
prime mover
by2product heat
%atch the words or the e&pressions with their de$initions"
$. sample a. a device or devices randomly chosen from o lot of
material. #ampling assumes that randomly selected devices
will exhibit characteristics during testing that are typical of
the lot as a whole
<. scaling b. a hardware device that is the central point, or one of
them, for a network, a unit that provides services, share its
resources and information with other computers, calledclients, on a network
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'. server c. the process of ending operation of a system or a
subsystem, following a defined procedure
*. shutdown d. the name given to any telecommunications systeminvolving the transmission of speech information, allowing
two or more persons to communicate verbally
0. solvency e. a box into which a computer user can type text, usually in
a word processor, within a formatting procedure or a
graphic
. telephony f. an operation performed by a digital processor to fill the
screen with an image not being displayed in the native
resolution of the L6: panel
&. text box g. an insidious and usually illegal computer program that
mas8uerades as a program that is useful, fun or otherwise
desirable for users to download to their system. Knce the
program is downloaded, it performs a destructive act
%. troIan horse h. abbreviation for /ninterruptible ower #upply, a standby
power source that provides power to a server or other
devices from a battery in the event of normal +6 power failure
-. /# i. ability of a fluid to dissolve inorganic materials and
polymers
Optical $iber communications
Kptical fiber communication is the method of transmitting informationthrough optical fibers. Kptical fibers can be used to transmit light and thus
information over long distances. )owadays, fiber2based systems have largely
replaced radio transmitter systems for long2haul optical data transmission. They
are largely used for telephony, but also for 3nternet traffic, long high2speed local
area networks (L+)s, cable2T>, and increasingly also for shorter distances.
6ompared to systems based on electrical cables, the approach of optical
fiber communications has advantages, the most important of which are7
The capacity of fibers for data transmission is huge7 a single fiber can carry
hundreds of thousands of telephone channels even without nearly utili9ing thefull theoretical capacity. 3n the last '1 years, the progress concerning
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transmission capacities of fiber links has been significantly faster than e.g. the
progress in the speed or storage capacity of computers.
The losses for light propagating in fibers are ama9ingly small7 about 1. <
d5Mkm for modern single2mode fibers, so that many tens of kilometres can be
bridged without amplifying the signals.+ large number of channels can be reamplified in a single fiber amplifier, if
re8uired for very large transmission distances.
:ue to the achievable huge transmission rate, the cost per transported bit
can be extremely low.
6ompared to electrical cables, fiber2optic cables are very lightweight, so
that the cost of laying a fiber2optic cable is much lower.
Biber2optic cables are immune to problems of electrical cables such as
ground loops or electromagnetic interference (A3.
=owever, fiber systems are somewhat more sophisticated to install and
operate, so that they tend to be less economical if their full transmission capacity
is not re8uired. Therefore, the Hlast mileH (the connection to the homes and
offices and usually still bridged with electrical cables, while fiber2based
communications do the bulk of the long2haul transmission. Gradually, however,
fiber communications are used within metropolitan areas, and currently we see
even the beginning of fiber to the home (BTT=, particularly in Fapan, where
private 3nternet users can already obtain affordable 3nternet connections with
data rates of $11 AbitMs J well above the performance of current +:#L systems,
which use electrical telephone lines.
Kptical fiber communications typically operate in a wavelength regioncorresponding to one of the following "telecom windows"7
The first window at %112-11 nm was originally used. Ga+s M +lGa+s2based
laser diodes and light2emitting diodes (L:s served as senders, and silicon
photodiodes were suitable for the receivers. =owever, the fiber losses are
relatively high in this region, and fiber amplifiers are not well developed for this
spectral region. Therefore, the first telecom window is suitable only for short2
distance transmission.
The second telecom window utili9es wavelengths around $.' Om, where the
fiber loss is much lower and the fiber dispersion is very small, so that dispersive broadening is minimi9ed. This window was originally used for long2haul
transmission. =owever, fiber amplifiers for $.' Om are not as good as their $.02
Om counterparts based on erbium, and 9ero dispersion is not necessarily ideal for
long2haul transmission, as it can increase the effect of optical nonlinearities.
The third telecom window, which is now very widely used, utili9es
wavelengths around $.0 Om. The fiber losses are lowest in this region, and
erbium2doped fiber amplifiers are available which offer very high performance.
Biber dispersion is usually anomalous but can be tailored with great flexibility
(dispersion2shifted fibers.
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Readin and vocabular!"
$. hat is optical fiber communication;
<. =ow can optical fibers be used;'. hich are the advantages of fiber communications;
*. hat are Telecom indows;
0. hich are the characteristics of the first window;
. hat about the second and the third window;
&. hy is optical fiber communication so important;
#ook up and $ind the meanin o$ the words and the e&pressions"
optical fiber
long2haul optical data
bulk
wavelength
broadening
counterparts
erbium
erbium2doped fiber
dispersion2shifted fiber
%atch the words or the e&pressions with their de$initions"
$. virtual
address
a. the address of a location in virtual storage? a virtual address
must be translated into a real address in order to process the
data in processor storage
<. wireless b. a lens with variable focal length providing the ability to
adIust the si9e on a screen by adIusting the 9oom lens, instead
of having to move the proIector closer or further
'. wi9ard c. in a user interface, to progressively increase or decrease the
si9e of a part of an image on a screen or in a window
*.workstation d. an insidious and usually illegal computer program that it
designed to replicate itself over a network for the purpose of
causing harm and M or destruction.
0. worm e. a dialog within an application that uses step2by2step
instructions to guide a user through a specific task
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. 9oom f. the term refers to telecommunication in which
electromagnetic waves, such as radio or television, to carry any
communications signal from one section of a communications
path to another
&. 9oom lens g. a computer, usually used on a network or a scientific
computer used for scientific application
%. cable
assembly
h. a designated memory holding area that temporarily stores
information copied or cut from a document, or files for transfer
-. clipboard i. fiber optic cable that has connectors installed on one or both
ends
$1.cluster I. a group of sectors on a hard drive that is addressed as one
logical unit by the operating system. 3t is also the smallest
contiguous area that can be allocated for the storage of data
even if actual data re8uire less storage
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Supplementar! te&ts"
Other sources o$ ener!
Kther power stations use the energy from wave or tidal motion, wind,sunlight or the energy of falling water, hydroelectricity. These types of energy
sources are called renewable energy.
H!droelectricit!7 =ydroelectric dams impound a reservoir of water and
release it through one or more water turbines to generate electricity.
Pumped storae7 + pumped storage hydroelectric power plant is a net
consumer of energy but decreases the price of electricity. ater is pumped to a
high reservoir during the night when the demand, and price, for electricity is
low. :uring hours of peak demand, when the price of electricity is high, the
stored water is released to produce electric power. #ome pumped storage plantsare actually not net consumers of electricity because they release some of the
water from the lower reservoir downstream, either continuously or in bursts.
Solar power7 + solar photovoltaic power plant converts sunlight directly
into electrical energy, which may need conversion to alternating current for
transmission to users. This type of plant does not use rotating machines for
energy conversion. #olar thermal electric plants are another type of solar power
plant. They direct sunlight using either parabolic troughs or heliostats. arabolic
troughs direct sunlight onto a pipe containing a heat transfer fluid, such as oil,
which is then used to boil water, which turns the generator. The central tower
type of power plant uses hundreds or thousands of mirrors, depending on si9e, to
direct sunlight onto a receiver on top of a tower. +gain, the heat is used to
produce steam to turn turbines. There is yet another type of solar thermal electric
plant. The sunlight strikes the bottom of the pond, warming the lowest layer
which is prevented from rising by a salt gradient. + Eankine cycle engine
exploits the temperature difference in the layers to produce electricity. )ot many
solar thermal electric plants have been built. Aost of them can be found in the
AoIave :esert, although #andia )ational Laboratory, 3srael and #pain have also
built a few plants.
Wind power7 ind turbines can be used to generate electricity in areaswith strong, steady winds. Aany different designs have been used in the past,
but almost all modern turbines being produced today use the :utch three2bladed,
upwind design. Grid2connected wind turbines now being built are much larger
than the units installed during the $-&1!s, and so produce power more cheaply
and reliably than earlier models. ith larger turbines (greater than $11 k, the
blades move more slowly than older, smaller (less than $11 k units, which
makes them less visually distracting and safer for airborne animals. =owever,
the old turbines can still be seen at some wind farms, particularly at +ltamont
ass and Tehachapi ass.
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1uclear power plant7 + nuclear power station7 The nuclear reactor is
contained inside the cylindrical containment buildings to the right 2 left is a
cooling tower venting water vapour from the )on2Eadioactive side of the plant.
+ nuclear power plant () is a thermal power station in which the heat
source is one or more nuclear reactors generating nuclear power. )uclear power plants are base load stations, which work best when the
power output is constant (although boiling water reactors can come down to half
power at night. Their units range in power from about *1 Ae to over $111
Ae. )ew units under construction in <110 are typically in the range 112$<11
Ae.
+s of <110 there are **' licensed nuclear power reactors in the world, of
which **$ are currently operational operating in '$ different countries. Together
they produce about $&P of the world!s electric power.
lectricity was generated for the first time by a nuclear reactor on
:ecember <1, $-0$ at the 5E23 experimental station near +rco, 3daho in the
/nited #tates. Kn Fune <&, $-0*, the world!s first nuclear power plant to
generate electricity for a power grid started operations at Kbninsk, /##E. The
world!s first commercial scale power station, 6alder =all in ngland opened in
$& Kctober, $-0.
T!pes o$ nuclear power plants
)uclear power plants are classified according to the type of reactor used.
=owever some installations have several independent units and these may usedifferent classes of reactor. 3n addition, some of the plant2types below in the
future may have passively safe features.
Fission reactors7 Bission power reactors generate heat by nuclear fission of
fissile isotopes of uranium and plutonium.
They may be further divided into three classes7
Thermal reactors use a neutron moderator to slow or moderate neutrons
so that they are more likely to produce fission. )eutrons created by fission are
high energy, or fast, and must have their energy decreased (be made thermal by
the moderator in order to efficiently maintain the chain reaction.Bast reactors sustain the chain reaction without needing a neutron
moderator. 5ecause they use different fuel than thermal reactors, the neutrons in
a fast reactor do not need to be moderated for an efficient chain reaction to
occur.
#ub2critical reactors use an outside source of neutrons rather than a chain
reaction to produce fission.
Fast reactors7 +lthough some of the earliest nuclear power reactors were
fast reactors, they have not as a class achieved the success of thermal reactors.
Bast reactors have the advantages that their fuel cycle can use all of the uraniumin natural uranium, and also transmute the longer2lived radioisotopes in their
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waste to faster2decaying materials. Bor these reasons they are inherently more
sustainable as an energy source than thermal reactors. #ee fast breeder reactor.
5ecause most fast reactors have historically been used for plutonium production,
they are associated with nuclear proliferation concerns.
Fusion reactors7 )uclear fusion offers the possibility of the release of verylarge amounts of energy with a minimal production of radioactive waste and
improved safety. =owever, there remain considerable scientific, technical, and
economic obstacles to the generation of commercial electric power using nuclear
fusion. 3t is therefore an active area of research, with very large2scale facilities
such as FT, 3TE, and the D machine.
+dvantages of nuclear power plants against other mainstream energy
resources are7 2 no greenhouse gas emissions (during normal operation 2
greenhouse gases are emitted only when the mergency :iesel Generators are
tested (the processes of uranium mining and of building and decommissioning
power stations produce relatively small amounts? 2 does not pollute the air 2
9ero production of dangerous and polluting gases such as carbon monoxide,
sulphur dioxide, aerosols, mercury, nitrogen oxides, particulates or
photochemical smog? 2 small solid waste generation (during normal operation?
low fuel costs 2 because so little fuel is needed? 2 large fuel reserves 2 again,
because so little fuel is needed? 2 nuclear batteries.
=owever, the disadvantages include7 2 risk of maIor accidents? 2 nuclear
waste 2 high level radioactive waste produced can remain dangerous for
thousands of years? 2 can help produce bombs? high initial costs? 2 high
maintenance costs? 2security concerns? high cost of decommissioning plants.
Telecommunication
Telecommunication is the transmission of signals over a distance for the
purpose of communication. Today this process almost always involves the
sending of electromagnetic waves by electronic transmitters but in earlier years
it may have involved the use of smoke signals, drums or semaphores. Today,
telecommunication is widespread and devices that assist the process such as the
television, radio and telephone are common in many parts of the world. There isalso a vast array of networks that connect these devices, including computer
networks, public telephone networks, radio networks and television networks.
6omputer communication across the 3nternet, such as e2mail and internet faxing,
is Iust one of many examples of telecommunication.
The word telecommunication was adapted from the Brench word
tQlQcommunication. 3t is a compound of the Greek prefix tele2 (RSU2, meaning
far offH, and communication, meaning exchange of informationH.
The basic elements of a telecommunication system are7
2 a transmitter that takes information and converts it to a signal for transmission
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2 a transmission medium over which the signal is transmitted
2 a receiver that receives and converts the signal back into usable
information
Bor example, consider a radio broadcast. 3n this case, the broadcast tower is
the transmitter, the radio is the receiver and the transmission medium is freespace. Kften telecommunication systems are two2way and devices act as both a
transmitter and receiver or transceiver. Bor example, a mobile phone is a
transceiver. Telecommunication over a phone line is called point2to2point
communication because it is between one transmitter and one receiver?
telecommunication through radio broadcasts is called broadcast communication
because it is between one powerful transmitter and numerous receivers.
#ignals can either be analogue or digital. 3n an analogue signal, the signal is
varied continuously with respect to the information. 3n a digital signal, the
information is encoded as a set of discrete values.
+ collection of transmitters, receivers or transceivers that communicate
with each other is known as a network. :igital networks may consist of one or
more routers that route data to the correct user. +n analogue network may
consist of one or more switches that establish a connection between two or more
users. Bor both types of network, a repeater may be necessary to amplify or
recreate the signal when it is being transmitted over long distances. This is to
combat noise which can corrupt the information carried by a signal.
+ channel is a division in a transmission medium so that it can be used to
send multiple independent streams of data. Bor example, a radio station may
broadcast at - A=9 while another radio station may broadcast at -*.0 A=9. 3nthis case the medium has been divided by fre8uency and each channel received a
separate fre8uency to broadcast on. +lternatively one could allocate each
channel a segment of time over which to broadcast.
The shaping of a signal to convey information is known as modulation.
Aodulation is a key concept in telecommunications and is fre8uently used to
impose the information of one signal on another. Aodulation is used to represent
a digital message as an analogue waveform. This is known as keying and several
keying techni8ues exist J these include phase2shift keying, amplitude2shift
keying and minimum2shift keying. 5luetooth, for example, uses phase2shiftkeying for exchanges between devices.
=owever, more relevant to earlier discussion, modulation is also used to
boost the fre8uency of analogue signals. This is because a raw signal is often not
suitable for transmission over free space due to its low fre8uencies. =ence its
information must be superimposed on a higher fre8uency signal (known as a
carrier wave before transmission.
Earl! telecommunications
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arly forms of telecommunication include smoke signals and drums.
:rums were used by natives in +frica, )ew Guinea and tropical +merica
whereas smoke signals were used by natives in +merica and 6hina. 6ontrary to
what one might think, these systems were often used to do more than merely
announce the presence of a camp.3n $&-<, a Brench engineer, 6laude 6happe built the first visual telegraphy
(or semaphore system between Lille and aris. This was followed by a line
from #trasbourg to aris. 3n $&-*, a #wedish engineer, +braham delcrant9 built
a 8uite different system from #tockholm to :rottningholm. +s opposed to
6happe!s system which involved pulleys rotating beams of wood, delcrant9!s
system relied only upon shutters and was therefore faster. =owever semaphore
as a communication system suffered from the need for skilled operators and
expensive towers often at intervals of only ten to thirty kilometres (six to
nineteen miles. +s a result, the last commercial line was abandoned in $%%1.
Teleraph and telephone
The first commercial electrical telegraph was constructed by #ir 6harles
heatstone and #ir illiam Bothergill 6ooke. 3t used the deflection of needles
to represent messages and started operating over thirteen miles (twenty2one
kilometres of the Great estern Eailway on - +pril $%'-. 5oth heatstone and
6ooke viewed their device as an improvement to the (existing electromagnetic
telegraphH not as a new device.
Kn the other side of the +tlantic Kcean, #amuel Aorse independentlydeveloped a version of the electrical telegraph that he unsuccessfully
demonstrated on < #eptember $%'&. #oon after he was Ioined by +lfred >ail
who developed the register J a telegraph terminal that integrated a logging
device for recording messages to paper tape. This was demonstrated successfully
over three miles (five kilometres on Fanuary $%'% and eventually over forty
miles (* kilometres between ashington, :6 and 5altimore on <* Aay $%**.
The patented invention proved lucrative and by $%0$ telegraph lines in the
/nited #tates spanned over <1,111 miles ('<,111 kilometres.
The first transatlantic telegraph cable was successfully completed on <&Fuly $%, allowing transatlantic telegraph communications for the first time.
arlier transatlantic cables installed in $%0& and $%0% only operated for a few
days or weeks before they failed.
The conventional telephone was invented by +lexander 5ell in $%&.
+lthough in $%*- +ntonio Aeucci invented a device that allowed the electrical
transmission of voice over a line. Aeucci!s device depended upon the
electrophonic effect and was of little practical value because it re8uired users to
place the receiver in their mouth to hearH what was being said.
The first commercial telephone services were set2up in $%&% and $%&- on both sides of the +tlantic in the cities of )ew =aven and London. 5ell held
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patents needed for such services in both countries. The technology grew 8uickly
from this point, with inter2city lines being built and exchanges in every maIor
city of the /nited #tates by the mid2 $%%1!s. :espite this, transatlantic
communication remained impossible for customers until Fanuary &, $-<& when a
connection was established using radio. =owever no cable connection existeduntil T+T2$ was inaugurated on #eptember <0, $-0 providing ' telephone
circuits.
Radio and television 3
3n $%'<, Fames Lindsay gave a classroom demonstration of wireless
telegraphy to his students. 5y $%0* he was able to demonstrate a transmission
across the Birth of Tay from :undee to oodhaven, a distance of two miles,
using water as the transmission medium.
+ddressing the Branklin 3nstitute in $%-', )ikola Tesla described and
demonstrated in detail the principles of wireless telegraphy. The apparatus that
he used contained all the elements that were incorporated into radio systems
before the development of the vacuum tube. =owever it was not until $-11, that
Eeginald Bessenden was able to wirelessly transmit a human voice. 3n :ecember
$-1$, Guglielmo Aarconi established wireless communication between 5ritain
and the /nited #tates earning him the )obel ri9e in physics in $-1- (which he
shared with 4arl 5raun.
Kn Aarch <0, $-<0, Fohn Logie 5aird was able to demonstrate the
transmission of moving pictures at the London department store #elfridges.=owever his device did not ade8uately display halftones and thus only presented
a silhouette of the recorded image. This problem was rectified in Kctober of that
year leading to a public demonstration of the improved device on < Fanuary
$-< again at #elfridges. 5aird!s device relied upon the )ipkow disk and thus
became known as the mechanical television. 3t formed the basis of experimental
broadcasts done by the 5ritish 5roadcasting 6orporation beginning #eptember
'1, $-<-.
=owever for most of the twentieth century televisions depended upon the
cathode ray tube invented by 4arl 5raun. The first version of such a television toshow promise was produced by hilo Barnsworth and demonstrated to his
family on #eptember &, $-<&. Barnsworth!s device would compete with the
work of >ladimir Dworykin who also produced a television picture in $-<- on a
cathode ray tube. Dworykin!s camera, which later would be known as the
3conoscope, had the backing of the influential Eadio 6orporation of +merica
(E6+ however eventually court action regarding the electron imageH between
Barnsworth and E6+ would resolve in Barnsworth!s favour.
Computer networks
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Kn #eptember $$, $-*1 George #tibit9 was able to transmit problems using
teletype to his 6omplex )umber 6alculator in )ew Nork and receive the
computed results back at :artmouth 6ollege in )ew =ampshire. This
configuration of a centrali9ed computer or mainframe with remote dumb
terminals remained popular throughout the $-01s. =owever it was not until the$-1s that researchers started to investigate packet switching J a technology that
would allow chunks of data to be sent to different computers without passing
through a centrali9ed mainframe, first. + four 2 node network emerged on
:ecember 0, $-- between the /niversity of 6alifornia, Los +ngeles, the
#tanford Eesearch 3nstitute, the /niversity of /tah and the /niversity of
6alifornia, #anta 5arbara. This network would become +E+)T, which by
$-%$ would consist of <$' nodes. 3n Fune $-&', the first non2/# node was
added to the network belonging to )orway!s )KE#+E proIect. This was shortly
followed by a node in London.
Telephone
Today, the fixed2line telephone systems in most residential homes remain
analogue and, although short2distance calls may be handled from end2to2end as
analogue signals, increasingly telephone service providers are transparently
converting signals to digital before, if necessary, converting them back to
analogue for reception. Aobile phones have had a dramatic impact on telephone
service providers. Aobile phone subscriptions now outnumber fixed line
subscriptions in many markets. #ales of mobile phones in <110 totalled %$.million with that figure being almost e8ually shared amongst the markets of
+siaMacific (<1*m, estern urope ($*m, 6A+ (6entral urope, the
Aiddle ast and +frica ($0'.0m, )orth +merica ($*%m and Latin +merica
($1<m. 3n terms of new subscriptions over the five years from $---, +frica has
outpaced other markets with 0%.<P growth compared to the next largest market,
+sia, which boasted '*.'P growth. 3ncreasingly these phones are being serviced
by digital systems such as G#A or 26:A+ with many markets choosing to
depreciate analogue systems such as +A#.
=owever there have been e8ually drastic changes in telephonecommunication behind the scenes. #tarting with the operation of T+T2% in $-%%,
the $--1s saw the widespread adoption of systems based around optic fibres.
The benefit of communicating with optic fibres is that they offer a drastic
increase in data capacity. T+T2% itself was able to carry $1 times as many
telephone calls as the last copper cable laid at that time and today!s optic fibre
cables are able to carry <0 times as many telephone calls as T+T2%. This rapid
increase in data capacity is due to several factors. Birst, optic fibres are
physically much smaller than competing technologies. #econd, they do not
suffer from crosstalk which means several hundred of them can be easily bundled together in a single cable. Lastly, improvements in multiplexing have
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lead to an exponential growth in the data capacity of a single fibre. This is due to
technologies such as dense wavelength2division multiplexing, which at its most
basic level is building multiple channels based upon fre8uency division as
discussed in the Technical foundations section. =owever despite the advances of
technologies such as dense wavelength2division multiplexing, technologies based around building multiple channels based upon time division such as
synchronous optical networking and synchronous digital hierarchy remain
dominant.
+ssisting communication across these networks is a protocol known as
+synchronous Transfer Aode (+TA. +s a technology, +TA arose in the $-%1s
and was envisioned to be part of the 5roadband 3ntegrated #ervices :igital
)etwork. The network ultimately failed but the technology gave birth to the
+TA Borum which in $--< published its first standard. Today, despite
competitors such as Aultiprotocol Label #witching, +TA remains the protocol
of choice for most maIor long2distance optical networks. The importance of the
+TA protocol was chiefly in its notion of establishing pathways for data through
the network and associating a traffic contract with these pathways. The traffic
contract was essentially an agreement between the client and the network about
how the network was to handle the data. This was important because telephone
calls could negotiate a contract so as to guarantee themselves a constant bit rate,
something that was essential to ensure the call could take place without a caller!s
voice being delayed in parts or cut2off completely.
Radio and television 4
The broadcast media industry is also at a critical turning point in its
development, with many countries starting to move from analogue to digital
broadcasts. The chief advantage of digital broadcasts is that they prevent a
number of complaints with traditional analogue broadcasts. Bor television, this
includes the elimination of problems such as snowy pictures, ghosting and other
distortion. These occur because of the nature of analogue transmission, which
means that perturbations due to noise will be evident in the final output. :igital
transmission overcomes this problem because digital signals are reduced to binary data upon reception and hence small perturbations do not affect the final
output.
3n digital television broadcasting, there are three competing standards that
are likely to be adopted worldwide. These are the +T#6, :>5 and 3#:5
standards and the adoption of these standards thus far is presented in the
captioned map. +ll three standards use AG2< for video compression. +T#6
uses :olby :igital +62' for audio compression, 3#:5 uses +dvanced +udio
6oding (AG2< art & and :>5 has no standard for audio compression but
typically uses AG2$ art ' Layer <. The choice of modulation also varies between the schemes. 5oth :>5 and 3#:5 use orthogonal fre8uency2division
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multiplexing (KB:A for terrestrial broadcasts (as opposed to satellite or cable
broadcasts where as +T#6 uses vestigial sideband modulation (>#5. KB:A
should offer better resistance to multi2path interference and the :oppler ffect
(which would impact reception using moving receivers. =owever controversial
tests conducted by the /nited #tates! )ational +ssociation of 5roadcasters haveshown that there is little difference between the two for stationary receivers.
3n digital audio broadcasting, standards are much more unified with
practically all countries (including 6anada choosing to adopt the :igital +udio
5roadcasting standard (also known as the ureka $*& standard.
=owever, despite the pending switch to digital, analogue receivers still
remain widespread. +nalogue television is still transmitted in practically all
countries. Bor analogue, there are three standards in use. These are known as
+L, )T#6 and #6+A. The basics of +L and )T#6 are very similar? a
8uadrature amplitude modulated sub2carrier carrying the chrominance
information is added to the luminance video signal to form a composite video
base2band signal (6>5#. The #6+A system, on the other hand, uses a
fre8uency modulation scheme on its colour sub2carrier. The name "hase
+lternating Line" describes the way that the phase of part of the colour
information on the video signal is reversed with each line, which automatically
corrects phase errors in the transmission of the signal by cancelling them out.
Bor analogue radio, the switch to digital is made more difficult by the fact that
analogue receivers cost a fraction of the cost of digital receivers.
The -nternet
Today an estimated $0.&P of the world population has access to the
3nternet with the highest concentration in )orth +merica (%.P,
KceaniaM+ustralia (0<.P and urope ('.$P. 3n terms of broadband access,
countries such as 3celand (<.& per $11, #outh 4orea (<0.* per $11 and the
)etherlands (<0.' per $11 lead the world. The 3nternational Telecommunication
/nion uses this information to compile a :igital +ccess 3ndex that measures the
overall ability of citi9ens to access and use information and communication
technologies. /sing this measure, countries such as #weden, :enmark and3celand receive the highest ranking while +frican countries such as )iger,
5urkina Baso and Aali receive the lowest.
The history of the 3nternet dates back to the early development of
communication networks. The idea of a computer network intended to allow
general communication between users of various computers has developed
through a large number of stages. The melting pot of developments brought
together the network of networks that we know as the 3nternet. This included
both technological developments and the merging together of existing network
infrastructure and telecommunication systems.
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The earliest versions of these ideas appeared in the late $-01s. ractical
implementations of the concepts began during the late $-1s and $-&1s. 5y the
$-%1s, technologies we now recogni9e as the basis of the modern 3nternet began
to spread over the globe. 3n the $--1s the introduction of the orld ide eb
( saw its use become commonplace.The infrastructure of the 3nternet spread across the globe to create the world
wide network of computers we know today. 3t spread throughout the estern
nations and then begged a penetration into the developing countries, thus
creating both unprecedented worldwide access to information and
communications and a digital divide in access to this new infrastructure. The
3nternet went on to fundamentally alter and affect the economy of the world,
including the economic implications of the dot2com bubble and offshore
outsourcing of hite2collar workers.
0e$ore the -nternet
rior to the widespread inter2networking that led to the 3nternet, most
communication networks were limited by their nature to only allow
communications between the stations on the network. #ome networks had
gateways or bridges between them, but these bridges were often limited or built
specifically for a single use. Kne prevalent computer networking method was
based on the central mainframe method, simply allowing its terminals to be
connected via long leased lines. This method was used in the $-01s by roIect
E+): to support researchers such as =erbert #imon, in ittsburgh,ennsylvania, when collaborating across the continent with researchers in #anta
Aonica, 6alifornia, on automated theorem proving and artificial intelligence.
1etworks that led to the -nternet
+RP+1ET7 romoted to the head of the information processing office at
+E+, Eobert Taylor intended to reali9e Licklider!s ideas of an interconnected
networking system. 5ringing in Larry Eoberts from A3T, he initiated a proIect
to build such a network. The first +E+)T link was established between the/niversity of 6alifornia, Los +ngeles and the #tanford Eesearch 3nstitute on <$
)ovember $--. 5y 0 :ecember $--, a *2node network was connected by
adding the /niversity of /tah and the /niversity of 6alifornia, #anta 5arbara.
5uilding on ideas developed in +LK=+ net, the +E+)T started in $-&< and
was growing rapidly by $-%$. The number of hosts had grown to <$', with a
new host being added approximately every twenty days.
+E+)T became the technical core of what would become the 3nternet,
and a primary tool in developing the technologies used. +E+)T development
was centred on the Ee8uest for 6omments (EB6 process, still used today for proposing and distributing 3nternet rotocols and #ystems. EB6 $, entitled
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=ost #oftwareH, was written by #teve 6rocker from the /niversity of
6alifornia, Los +ngeles, and published on +pril &, $--.
-nternet protocol suite
ith so many different network methods, something needed to unify them.
Eobert . 4ahn of :+E+ and +E+)T recruited >int 6erf of #tanford
/niversity to work with him on the problem. 5y $-&', they had soon worked
out a fundamental reformulation, where the differences between network
protocols were hidden by using a common internetwork protocol, and instead of
the network being responsible for reliability, as in the +E+)T, the hosts
became responsible. 6erf credits =ubert Dimmerman and Louis ou9in
(designer of the 6N6L+:# network with important work on this design.
ith the role of the network reduced to the bare minimum, it became
possible to Ioin almost any networks together, no matter what their
characteristics were, thereby solving 4ahn!s initial problem. :+E+ agreed to
fund development of prototype software, and after several years of work, the
first somewhat crude demonstration of what had by then become T6M3
occurred in Fuly $-&&. This new method 8uickly spread across the networks, and
on Fanuary $, $-%', T6M3 protocols became the only approved protocol on the
+E+)T, replacing the earlier )6 protocol.
+RP+1ET to 1SF1et
+fter the +E+)T had been up and running for several years, +E+
looked for another agency to hand off the network to? +E+!s primary business
was funding cutting2edge research and development, not running a
communications utility. ventually, in Fuly $-&0, the network had been turned
over to the :efence 6ommunications +gency, also part of the :epartment of
:efence. 3n $-%', the /.#. military portion of the +E+)T was broken off as
a separate network, the A3L)T.The networks based around the +E+)T were government funded and
therefore restricted to non2commercial uses such as research? unrelated
commercial use was strictly forbidden. This initially restricted connections to
military sites and universities. :uring the $-%1s, the connections expanded to
more educational institutions, and even to a growing number of companies such
as :igital 8uipment 6orporation and =ewlett2ackard, which were
participating in research proIects or providing services to those who were.
+nother branch of the /.#. government, the )ational #cience Boundation
()#B, became heavily involved in internet research and started development of a successor to +E+)T. 3n $-%* this resulted in the first ide +rea )etwork
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designed specifically to use T6M3. This grew into the )#B)et backbone,
established in $-%, and intended to connect and provide access to a number of
supercomputing centres established by the )#B.
The transition toward an -nternet
3t was around the time when +E+)T began to merge with )#B)et,
which the term 3nternet originated, with "an internet" meaning any network
using T6M3. "The 3nternet" came to mean a global and large network using
T6M3, which at the time meant )#B)et and +E+)T. reviously "internet"
and "internet work" had been used interchangeably, and "internet protocol" had
been used to refer to other networking systems such as Cerox )etwork #ervices.
+s interest in wide spread networking grew and new applications for it
arrived, the 3nternet!s technologies spread throughout the rest of the world.
T6M3!s network2agnostic approach meant that it was easy to use any existing
network infrastructure, such as the 3## C.<0 network, to carry 3nternet traffic.
3n $-%*, /niversity 6ollege London replaced its transatlantic satellite links with
T6M3 over 3##.
Aany sites unable to link directly to the 3nternet started to create simple
gateways to allow transfer of e2mail, at that time the most important application.
#ites which only had intermittent connections used //6 or Bido)et and reliedon the gateways between these networks and the 3nternet. #ome gateway
services went beyond simple e2mail peering, such as allowing access to BT
sites via //6 or e2mail.
The first +E+)et connection outside the /# was established to )KE#+E
in )orway in $-&', Iust ahead of the connection to Great 5ritain. These links
were all converted to T6M3 in $-%<, at the same time as the rest of the +rpanet.
CER15 the European internet5 the link to the Paci$ic and be!ond
3n $-%* the move in urope towards more widespread use of T6M3
started, and 6E)T was converted over to using it. The T6M3 6E)T
remained isolated from the rest of the 3nternet, forming a small internal internet
until $-%-.
3n $-%% :aniel 4arrenberg, from 63 in +msterdam, visited 5en #egal,
6E)!s T6M3 6oordinator? looking for advice about the transition of the
uropean side of the //6 /senet network (much of which ran over C.<0
links over to T6M3. 3n $-%&, 5en #egal had met with Len 5osack from the
then still small company 6isco about T6M3 routers, and was able to give4arrenberg advice and forward him on to 6isco for the appropriate hardware.
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This expanded the uropean portion of the 3nternet across the existing //6
networks, and in $-%- 6E) opened its first external T6M3 connections. This
coincided with the creation of EQseaux 3 uropQens (E3, initially a group of
3 network administrators who met regularly to carry out co2ordination work
together. Later, in $--<, E3 was formally registered as a cooperative in+msterdam.
+t the same time as the rise of internetworking in urope, ad2hoc
networking to +E+ and in2between +ustralian colleges formed, based on
various technologies such as C.<0 and //6)et. These were limited in their
connection to the global networks, due to the cost of making individual
international //6 dial2up or C.<0 connections. 3n $-%-, +ustralian colleges
Ioined the push towards using 3 protocols to unify their networking
infrastructures. ++E)et was formed in $-%- by the +ustralian >ice2
6hancellors! 6ommittee and provided a dedicated 3 based network for
+ustralia.
The 3nternet began to penetrate +sia in the late $-%1s. Fapan, which had
built the //62based network F/)T in $-%*, connected to )#B)et in $-%-.
3t hosted the annual meeting of the 3nternet #ociety, 3)T!-<, in 4obe.
#ingapore developed T6=)T in $--1, and Thailand gained a global 3nternet
connection between 6hulalongkorn /niversity and //)T in $--<.
+ diital divide
hile developed countries with technological infrastructures were Ioiningthe 3nternet, developing countries began to experience a digital divide separating
them from the 3nternet. +t the beginning of the $--1s, +frican countries relied
upon C.<0 3## and <*11 baud modem //6 links for international and
internet work computer communications. 3n $-- a /#+3: funded proIect, the
Leland initiative, started work on developing full 3nternet connectivity for the
continent. Guinea, Ao9ambi8ue, Aadagascar and Ewanda gained satellite earth
stations in $--&, followed by 6Vte d!3voire and 5enin in $--%.
3n $--$ 6hina saw its first T6M3 college network, Tsinghua /niversity!s
T/)T. 6hina went on to make its first global 3nternet connection in $--*, between the 5eiIing lectro2#pectrometer 6ollaboration and #tanford
/niversity!s Linear +ccelerator 6enter. =owever, 6hina went on to implement
its own digital divide by implementing a country2wide content filter.
Openin the network to commerce
The interest in commercial use of the 3nternet became a hotly debated
topic. +lthough commercial use was forbidden, the exact definition of
commercial use could be unclear and subIective. veryone agreed that onecompany sending an invoice to another company was clearly commercial use,
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but anything less was up for debate. //6)et and the C.<0 3## had no such
restrictions, which would eventually see the official barring of //6)et use of
+E+)T and )#B)et connections. #ome //6 links still remained
connecting to these networks however, as administrators cast a blind eye to their
operation.:uring the late $-%1s, the first 3nternet service provider (3# companies
were formed. 6ompanies like #3)et, //)T, )etcom, and ortal #oftware
were formed to provide service to the regional research networks and provide
alternate network access, //62based email and /senet )ews to the public.
The first dial2up 3#, world.std.com, opened in $-%-.
This caused controversy amongst university users, who were outraged at
the idea of non2educational use of their networks. ventually, it was the
commercial 3nternet service providers who brought prices low enough that
Iunior colleges and other schools could afford to participate in the new arenas of
education and research.
5y $--1, +E+)T had been overtaken and replaced by newer
networking technologies and the proIect came to a close. 3n $--*, the )#B)et,
now renamed +)#)T (+dvanced )etworks and #ervices and allowing non2
profit corporations access, lost its standing as the backbone of the 3nternet. 5oth
government institutions and competing commercial providers created their own
backbones and interconnections. Eegional network access points ()+s
became the primary interconnections between the many networks and the final
commercial restrictions ended.
Email and ,senet 6 The rowth o$ the te&t $orum
2mail is often called the killer application of the 3nternet. =owever, it
actually predates the 3nternet and was a crucial tool in creating it. 2mail started
in $-0 as a way for multiple users of a time2sharing mainframe computer to
communicate. +lthough the history is unclear, among the first systems to have
such a facility were #:6!s @'< and A3T!s 6T##.
The +E+)T computer network made a large contribution to the
evolution of e2mail. There is one report indicating experimental inter2system e2mail transfers on it shortly after +E+)T!s creation. 3n $-&$ Eay Tomlinson
created what was to become the standard 3nternet e2mail address format, using
the W sign to separate user names from host names.
+ number of protocols were developed to deliver e2mail among groups of
time2sharing computers over alternative transmission systems, such as //6
and 35A!s >)T e2mail system. 2mail could be passed this way between a
number of networks, including +E+)T, 53T)T and )#B)et, as well as to
hosts connected directly to other sites via //6.
3n addition, //6 allowed the publication of text files that could be read by many others. The )ews software developed by #teve :aniel and Tom
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Truscott in $-&- was used to distribute news and bulletin board2like messages.
This 8uickly grew into discussion groups, known as newsgroups, on a wide
range of topics. Kn +E+)T and )#B)et similar discussion groups would
form via mailing lists, discussing both technical issues and more culturally
focused topics.
+ world librar! 6 From opher to the WWW
The first orld ide eb server, currently in the 6E) museum, labelled
"This machine is a server. :K )KT KE :K)XX"
+s the 3nternet grew through the $-%1s and early $--1s, many people
reali9ed the increasing need to be able to find and organi9e files and
information. roIects such as Gopher, +3#, and the BT +rchive list attempted
to create ways to organi9e distributed data. /nfortunately, these proIects fell
short in being able to accommodate all the existing data types and in being able
to grow without bottlenecks.
Kne of the most promising user interface paradigms during this period was
hypertext. The technology had been inspired by >annevar 5ush!s "memex" and
developed through Ted )elson!s research on roIect Canadu and :ouglas
ngelbart!s research on )L#. Aany small self2contained hypertext systems had
been created before, such as +pple 6omputer!s =yper6ard.
3n $--$, Tim 5erners2Lee was the first to develop a network2based
implementation of the hypertext concept. This was after 5erners2Lee had
repeatedly proposed his idea to the hypertext and 3nternet communities atvarious conferences to no avail 2 no one would implement it for him. orking at
6E), 5erners2Lee wanted a way to share information about their research. 5y
releasing his implementation to public use, he ensured the technology would
become widespread. #ubse8uently, Gopher became the first commonly2used
hypertext interface to the 3nternet. hile Gopher menu items were examples of
hypertext, they were not commonly perceived in that way.
+n early popular web browser, modelled after =yper6ard, was
>iola. 3t was eventually replaced by, Aosaic in terms of popularity.
Aosaic a graphical browser for the , was developed by a team at the )ational 6enter for #upercomputing +pplications at the /niversity of 3llinois at
/rbana26hampaign ()6#+2/3/6, and led by Aarc +ndreessen. Bunding for
Aosaic came from the =igh2erformance 6omputing and 6ommunications
3nitiative, a funding program initiated by then2#enator +l Gore!s =igh
erformance 6omputing +ct of $--$. Aosaic!s graphical interface soon became
more popular than Gopher, which at the time was primarily text2based, and the
became the preferred interface for accessing the 3nternet. The orld
ide eb has led to a widespread culture of individual self publishing and co2
operative publishing.
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Findin what !ou need 6 The search enine
ven before the orld ide eb, there were search engines that attempted
to organi9e the 3nternet. The first of these was the +rchie search engine from
AcGill /niversity in $--1, followed in $--$ by +3# and Gopher. +ll three of those systems predated the invention of the orld ide eb but all continued to
index the eb and the rest of the 3nternet for several years after the eb
appeared. There are still Gopher servers as of <11, although there are a great
many more web servers.
+s the eb grew, search engines and eb directories were created to track
pages on the eb and allow people to find things. The first full2text eb search
engine was eb6rawler in $--1. 5efore eb6rawler, only eb page titles were
searched. +nother early search engine, Lycos, was created in $--' as a
university proIect, and was the first to be commercially successful. 5y +ugust
<11$, Google tracked over $.' billion web pages and the growth continues,
although the real advances are not in terms of database si9e, but relevancy
ranking, the methods by which search engines attempt to sort the best results
first. +lgorithms for this have continuously improved since circa $--, when it
became a maIor issue, due to the rapid growth of the web, which made it
impractical for searchers to look through the entire list of results. +s of <11 the
rankings are more important than ever, since looking through the entire list of
results is not so much impractical as humanly impossible, since for popular
topics new pages appear on the web faster than anyone could read them all.
Google!s age Eank method for ordering the results has received the most press, but all maIor search engines continually refine their ranking methodologies with
a view toward improving the ordering of results.
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