Transcript Global Applications

3. Global Applications
CS100: The World of Computing
John Dougherty
Haverford College
Overview
 Revisit Applications
 General Networking and Data
Communication
 The Internet
 The World Wide Web
 Benefits, Side Effects and Consequences
Recall: A program …
… is an implementation of an algorithm
… transforms input data into output data
… is a set of instructions
… is a collection of methods used to
manipulate the properties of objects (OOP)
… is where algorithm meets data structure
(classic view)
Computation and Storage
computation
storage
algorithms + data structures == programs
Overlap includes …
… storage needed to perform a computation
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Registers
Cache
… computation needed to access (i.e., store or
retrieve) storage
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Device driver software
Natural Interdependence
Communication
 Transmission of data from one time/place to
another time/place
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verbal
written
smoke signals
gesturing
icons
Data and Information
 Data is communicated
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Ink on paper (or even lower-level)
Electric signals on a wire
Lights at an intersection
 Information is abstracted from the data
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Poetry, warnings
Stop, yield or go
Computers and Communication
 Mainframes – centralized (i.e., planet)
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Easy to access everything in the “universe”
Single point of failure
 PCs – decentralized (i.e., islands)
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Independent  fault tolerant
Hard to access distributed information
 Networking – balance (islands with bridges)
A more complete picture
computation
communication
storage
Types of Networks
 LAN: Local Area Networks
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Ethernet, FDDI, token-ring
 Internet
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Decentralized, nested
 Intranet
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Private network, secure, uses Internet protocols
 Extranet
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Part of intranet extended to include partners, customers
Internet
 Initials Goals:
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Connect research computers
Fault tolerant  decentralized
 Features
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Packet-switched
Layered
Routers use IP address to forward to destination
A Sample Network
Message
Destination
Source
Circuit Switching
Destination
Circuit
Source
Packet Switching
Destination
Source
Packet
General IP Packet Structure
Sequence Number
Destination Address
Source Address
Packet Data
Checksum
Some Internet Applications
 ftp: file transfer protocol
 email
 telnet: remote interaction with O/S
 newsgroups
 gopher
 www: World Wide Web
World Wide Web
 Most visible Internet Application
 Multiple protocols
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ftp
http: hypertext transfer protocol
file: local file access
 Languages for information interchange
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HTML, DHTML, VRML, XML
Components of the WWWeb
Hypertext
Client – Server
Computing
Internet
Multimedia
Component Definitions
 Hypertext: text that can be read in a nonlinear manner; permits the reader to “go as
deep” as required or desired
 Client-Server Computing: separation of the
interface from the application so each can
reside on the same or different computers
 Multimedia: merging text, graphics, sound,
and animation into a single document
Communication:
Conventional vs. IT
 Temporally Distinct, Point-to-Point
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US mail
Email
 Temporally Distinct, Indirect
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Bulletin Board
Newsgroup
Server – “Homework Drop Box”
Communication:
Conventional vs. IT
 Temporally Connected, Broadcast
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Shout (local), megaphone, radio
Post on web/newsgroup, spam
 Temporally Connected, Multicast
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Telephone party line
Chat room
Nextel Direct feature
Implications (3.6)
 Freedom of Speech
 Privacy
 Information Quality
 (Too) Easy Access to All Information
 Intellectual Property
 Others …