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 …