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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 8186 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 42 00101010 • Text • Pictures IT 01001010 01010100 .gif, .jpeg, .bmp,… • Audio 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: 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 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 •No single •No single •No single authority control source entry point 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 ISP Carriers 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. 0110110111101111101111101010110111……….01110 Packets Message 01101010101000010101011100 01101010101000010101011100 …….. 01101010101000010101011100 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 HTTP SSL TCP IP Ethernet Coaxial Cable, Twisted Pair 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 TCP OVER IP seanjtaylor.com From: 128.122.199.131 To: IPXpress 216.115.102.78 Internet Delivery Envelope IP and TCP protocols allow any two computers on the Internet to exchange data www.yahoo.com 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