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INFORMATION TECHNOLOGY IN BUSINESS AND SOCIETYSESSION 6 – HOW COMPUTERS AND THE WEB WORK
SEAN J. TAYLOR
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ADMINISTRATIVIA
• Facebook Experiment: See Beibei Li in 8-186 Friday 2pm-4pm to receive payment
• Varun’s office hours on Monday: 2-4pm in 8th floor tutoring area
• Assignment 1• My office hours: moved to 3:30-5:30pm on
FRIDAY (temporarily)
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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.
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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
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BASIC COMPUTER ARCHITECTURE:INFORMATION REPRESENTATION• Numbers
• Text
• Pictures
• Audio
42 00101010
IT 01001010 01010100
.gif, .jpeg, .bmp,…
AU-Sun, WAV-MS, AIF-Apple, MP3
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Understanding Binary:ASCII coding scheme
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FROM ANALOG TO DIGITAL DATA000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011
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FROM ANALOG TO DIGITAL DATA000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011
000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011
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BASIC COMPUTER ARCHITECTURE
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UBIQUITOUS COMPUTING
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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: 286386486Pentium I,II,III,IV, AMD 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
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TELLING COMPUTERS WHAT TO DO
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THE INTERNET
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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
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HOW IT BEGAN: THE INTERNET IN 1969
Interface Message Processors (IMPs) – packet switching nodes used to connect to ARPANET
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ARPANET 1971
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ARPANET 1980
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SIMPLIFIED STRUCTURE OF THE INTERNETHierarchy 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
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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
ISPISP
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THE INTERNET
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THE INTERNET
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LAYERS
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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.
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PACKET-SWITCHED NETWORKSData 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
Packets0110110111101111101111101010110111……….01110
Message
Network
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PROTOCOLS AND TCP/IPEffective communication requires rules
• Protocol: A set of rules for transmitting data between computers
• Example: TCP/IPThe ‘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
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OSI 7 LAYER MODEL
Coaxial Cable, Twisted Pair
EthernetIPTCP
HTTPSSL
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INTERNET PROTOCOLEach 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
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From:
128.122.199.131
To:
216.115.102.78 IPXpressInternet Delivery Envelope
seanjtaylor.com
www.yahoo.com
TCP OVER IP
IP and TCP protocols allow any two computers on the Internet to exchange data
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TRANSMISSION CONTROL PROTOCOL
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DNS: UNDERSTANDING DOMAINSDNS 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?
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HTTP: HYPERTEXT TRANSFER PROTOCOL
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HTTP IN ACTION
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“THE ELEMENTS OF COMPUTING SYSTEMS”“WEAVING THE WEB” (TIM BERNERS-LEE)
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NEXT CLASS:COMPUTERS AND THE WEB II
• HTML tutorial