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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: 286386486Pentium 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