1. 3. Global Applications CS100: The World of Computing John Dougherty Haverford College

2. Overview  Revisit Applications  General Networking and Data Communication  The Internet  The World Wide Web  Benefits, Side Effects and Consequences

3. 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)

4. Computation and Storage computation storage algorithms + data structures == programs

5. 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

6. Communication  Transmission of data from one time/place to another time/place verbal written smoke signals gesturing icons

7. 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

8. 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)

9. A more complete picture computation storage communication

10. Types of Networks  LAN: Local Area Networks Ethernet, FDDI, token-ring  Internet Decentralized, nested  Intranet Intranet Private network, secure, uses Internet protocols  Extranet Extranet Part of intranet extended to include partners, customers

11. Internet  Initials Goals: Connect research computers Fault tolerant  decentralized  Features Packet-switched Layered Routers use IP address to forward to destination

12. A Sample Network Source Destination Message

13. Circuit Switching Circuit Source Destination

14. Packet Switching Source Destination Packet

15. General IP Packet Structure Sequence Number Source Address Destination Address Packet Data Checksum

16. Some Internet Applications  ftp: file transfer protocol  email  telnet: remote interaction with O/S  newsgroups  gopher  www: World Wide Web

17. 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

18. Components of the WWWeb Internet Client – Server Computing Hypertext Multimedia

19. 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

20. Communication: Conventional vs. IT  Temporally Distinct, Point-to-Point US mail Email  Temporally Distinct, Indirect Bulletin Board Newsgroup Server – “Homework Drop Box”

21. 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

22. Implications (3.6)  Freedom of Speech  Privacy  Information Quality  (Too) Easy Access to All Information  Intellectual Property  Others …