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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 - PowerPoint PPT Presentation
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INFORMATION TECHNOLOGY IN BUSINESS AND SOCIETYSESSION 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 8th 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 DATA000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011
FROM ANALOG TO DIGITAL DATA000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011
000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011
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: 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
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 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
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
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 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
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
OSI 7 LAYER MODEL
Coaxial Cable, Twisted Pair
EthernetIPTCP
HTTPSSL
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
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
TRANSMISSION CONTROL PROTOCOL
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?
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