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26 Οκτ 2013 (πριν από 4 χρόνια και 2 μήνες)

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INFORMATION
TECHNOLOGY IN
BUSINESS AND
SOCIETY

SESSION 6


HOW COMPUTERS AND THE WEB WORK

SEAN J.
TAYLOR

ADMINISTRATIVIA


Facebook Experiment: See
Beibei

Li in 8
-
186 Friday 2pm
-
4pm to receive payment


Varun’s

office hours on Monday: 2
-
4pm in
8
th

floor tutoring area


Assignment 1


My office hours: moved to 3:30
-
5:30pm on
FRIDAY (temporarily)

LEARNING OBJECTIVES

1.
Understand basic computer architecture and
how it has been enabled by layering platforms
and Moore’s law.

2.
Be able to explain how the Internet functions at
a high level.

WHY WE CARE?









“We’re
in an engineering culture. You couldn’t
put a [Rupert] Murdoch or a [Michael] Eisner
in charge of a company [like Google]. It’s
been tried. Terry
Semel

led Yahoo. I just
spent some time with Google engineers. I
couldn’t understand a thing they were
saying. I don’t think [
Semel
] understood the
engineers’ language, so he couldn’t
challenge them. I suspect that’s one reason
he didn’t
last”

Ken
Auletta
, SIIA keynote, 1/30/2008

BASIC COMPUTER
ARCHITECTURE:

INFORMATION REPRESENTATION


Numbers




Text




Pictures




Audio




42


00101010

IT


01001010 01010100

.gif, .jpeg, .bmp,…

AU
-
Sun, WAV
-
MS, AIF
-
Apple, MP3

Understanding Binary:
ASCII coding scheme

FROM ANALOG TO DIGITAL DATA

000000000000

000111111000

001100001100

001000000100

010010010010

010000000010

010000000010

001011110100

001100001100

000111111000

000000000011

000000000011

FROM ANALOG TO DIGITAL DATA

000000000000

000111111000

001100001100

001000000100

010010010010

010000000010

010000000010

001011110100

001100001100

000111111000

000000000011

000000000011

000000000000

000111111000

001100001100

001000000100

010010010010

010000000010

010000000010

001011110100

001100001100

000111111000

000000000011

000000000011

BASIC COMPUTER
ARCHITECTURE

UBIQUITOUS COMPUTING


COMPUTER BASICS:
HARDWARE


Central processing unit (CPU):

the actual hardware that
interprets and executes software instructions and
coordinates how all the other hardware devices work
together.


Intel
: 286

386

486

Pentium
I,II,III,IV, AM
D
Athlon,
IBM PowerPC,
Sun SPARC, MIPS


Random
Access Memory (RAM)
: The place to keep the data
and applications while the computer is
running


Storage:

A tool you use to store information for use at a later
time


floppy
disks, CD, DVD, Hard Disks,
tape


TELLING COMPUTERS WHAT TO DO

THE INTERNET

WHAT IS THE INTERNET?


A very large network of computers that “speak” IP (and usually TCP as well)


All connected to each other (hence a “network”)


Information exchanged between two computers may pass through several
other computers

HOW IT BEGAN: THE INTERNET IN 1969

Interface Message Processors

(IMPs)


packet switching nodes
used to connect to ARPANET

ARPANET 1971


ARPANET 1980


SIMPLIFIED STRUCTURE OF THE INTERNET


Hierarchy of privately
-
owned networks


Backbone

network: High speed, city
-
to
-
city, with network access
points, owned by large service providers (AT&T, Sprint, Level3)


ISP

networks: Connect from backbone to local areas (typically
providing access to consumers)


Local access networks
: Access to individual computers

Internet:


No single authority


No single control source


No single entry point


No single type of application

INTERNET BACKBONE


Set of interconnected Wide Area Networks (WANs)


Similar to the Interstate Highway network


WAN owners (backbone providers) compete with each other


Several connections converge at a Network Access Point
(NAP). Each NAP has at least one intelligent device


transitional data communication facilities.


Backbone providers own and maintain devices at NAPs


Internet Backbone

Carriers

ISP

ISP

THE INTERNET








THE INTERNET








LAYERS

WHY IS INTERNET STRUCTURE
STRATEGIC?

Resilient. One node goes down, others don’t.

Intelligence is at the edges.

Content agnostic.

Application agnostic.

No single authority controls it.

Extensible


Can always add more.



PACKET
-
SWITCHED NETWORKS


Data is sent as a sequence of ‘packets’


Packet Switched vs. Circuit Switched Networks


It isn’t cost effective to have telephone
-
like connections
between different communicating computers


This is primarily because data transmission is ‘bursty’



Packetize,
transmit, reassemble.

……..

01101010101000010101011100

01101010101000010101011100

01101010101000010101011100

Packets

0110110111101111101111101010110111……….01110

Message

Network

PROTOCOLS AND TCP/IP

Effective communication requires rules


Protocol: A set of rules for transmitting data
between computers


Example: TCP/IP

The ‘rules’ in a protocol answer questions like:


How do I write down the address of the computer I
want to send my packet to?


Where do I send the next packet I get?


How do I detect the beginning of a new packet?


How do I figure out an error in transmission?


IP address


32
-
bit number given to each device connected to the
Internet

OSI 7 LAYER MODEL

Coaxial Cable,
Twisted Pair

Ethernet

IP

TCP

HTTP

SSL

INTERNET PROTOCOL


Each Internet computer (host) has an
IP address


String of 32 ones and zeros (IPv4
-
> IPv6)


Usually represented by four number segments separated by dots: dotted
decimal notation, e.g., 128.171.17.13


IP names

(e.g., www2.nyu.edu) correspond to IP addresses

Routers


Connect the Internet’s individual networks (subnets)


Cooperate to give an end
-
to
-
end route for each packet


Need to be very fast


Who is the world’s leading

seller of routers?


127.18.47.145

127.47.17.47

From:

128.122.199.131

To:

216.115.102.78

IP
Xpress

Internet Delivery Envelope

seanjtaylor.com

www.yahoo.com

TCP OVER IP

IP and TCP protocols allow any two computers on
the Internet to exchange data

TRANSMISSION CONTROL
PROTOCOL

DNS: UNDERSTANDING DOMAINS


DNS is the Internet’s “directory assistance” linking IP names to IP addresses

A computer’s IP name tells you a lot; e.g., the type of organization supporting
the Web site

Top
-
level domain: the last part of IP names, e.g.,


com


commercial or for
-
profit business


edu



educational institution


gov



U.S. government agency


mil


U.S. military organization


net


Internet administrative organization


org


professional or non
-
profit organization


biz


business


pro


accountants, doctors, and lawyers, to start

How do you get a domain name?

HTTP:

HYPERTEXT TRANSFER PROTOCOL

HTTP IN ACTION

“THE ELEMENTS OF COMPUTING SYSTEMS”

“WEAVING THE WEB” (TIM BERNERS
-
LEE)

NEXT CLASS:

COMPUTERS AND THE WEB II


HTML tutorial