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 Registers Cache
… computation needed to access (i.e., store or retrieve) storage Device driver software
Natural Interdependence
Communication
Transmission of data from one time/place to another time/place verbal written smoke signals gesturing icons
Data and Information
Data is communicated Ink on paper (or even lower-level) Electric signals on a wire Lights at an intersection
Information is abstracted from the data Poetry, warnings Stop, yield or go
Computers and Communication
Mainframes – centralized (i.e., planet) Easy to access everything in the “universe” Single point of failure
PCs – decentralized (i.e., islands) Independent fault tolerant Hard to access distributed information
Networking – balance (islands with bridges)
A more complete picture
computation storage
communication
Types of Networks
LAN: Local Area Networks Ethernet, FDDI, token-ring
Internet Decentralized, nested
Intranet Private network, secure, uses Internet protocols
Extranet Part of intranet extended to include partners, customers
Internet
Initials Goals: Connect research computers Fault tolerant decentralized
Features Packet-switched Layered Routers use IP address to forward to destination
A Sample Network
Source
DestinationMessage
Circuit Switching
Circuit
Source
Destination
Packet Switching
Source
Destination
Packet
General IP Packet Structure
Sequence Number
Source Address
Destination 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
ftp http: hypertext transfer protocol file: local file access
Languages for information interchange HTML, DHTML, VRML, XML
Components of the WWWeb
Internet
Client – ServerComputing
Hypertext Multimedia
Component Definitions
Hypertext: text that can be read in a non-linear 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 US mail Email
Temporally Distinct, Indirect Bulletin Board Newsgroup Server – “Homework Drop Box”
Communication:Conventional vs. IT
Temporally Connected, Broadcast Shout (local), megaphone, radio Post on web/newsgroup, spam
Temporally Connected, Multicast 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 …