 2001 Prentice Hall, Inc. All rights reserved. Chapter 1 – Introduction to Computers, the Internet and the World Wide Web Outline 1.1Introduction 1.2What is a Computer? 1.3Computer Organization 1.4Evolution of Operating Systems 1.5Personal Computing, Distributed Computing and Client/ Server Computing 1.6Machine Languages, Assembly Languages and High-level Languages 1.7Structured Programming 1.8Object-Oriented Programming 1.9Hardware Trends 1.10History of the Internet 1.11History of the World Wide Web 1.12History of Perl

 2001 Prentice Hall, Inc. All rights reserved. Chapter 1 – Introduction to Computers, the Internet and the World Wide Web Outline 1.13Perl Library 1.14General Notes About Perl and This Book

 2001 Prentice Hall, Inc. All rights reserved. 1.1 Introduction We will learn –How to use Perl with the Common Gateway Interface (CGI) for building dynamic, Web-based applications This course is appropriate for –Novices with little or no programming experience –Experienced professionals building substantial information systems

 2001 Prentice Hall, Inc. All rights reserved. 1.2 What is a Computer? Computer –Device capable of performing computations and making logical decisions –Computers process data under the control of sets of instructions called computer programs Hardware –Various devices comprising a computer –Keyboard, screen, mouse, disks, memory, CD-ROM, and processing units Software –Programs that run on a computer

 2001 Prentice Hall, Inc. All rights reserved. 1.3 Computer Organization Logical units of a computer –Input unit –Output unit –Memory unit –Arithmetic and logic unit (ALU) –Central processing unit (CPU) –Secondary storage unit

 2001 Prentice Hall, Inc. All rights reserved. 1.4 Evolution of Operating Systems Batch processing in early systems Operating systems –Early systems increased throughput –Multiprogramming “Simultaneous” operation of many jobs –Timesharing Many users sharing a computer at once Development of UNIX

 2001 Prentice Hall, Inc. All rights reserved. 1.5 Personal Computing, Distributed Computing, and Client/Server Computing Personal computers –Economical enough for individual Distributed computing –Computing distributed over networks Client/server computing –Sharing of information across computer networks between file servers and clients (personal computers)

 2001 Prentice Hall, Inc. All rights reserved. 1.6 Machine Languages, Assembly Languages and High-level Languages Three types of programming languages 1.Machine languages Strings of numbers giving machine specific instructions Example: Assembly languages English-like abbreviations representing elementary computer operations (translated via assemblers) Example: LOAD BASEPAY ADD OVERPAY STORE GROSSPAY

 2001 Prentice Hall, Inc. All rights reserved. 1.6 Machine Languages, Assembly Languages and High-level Languages 3.High-level languages Codes similar to everyday English Use mathematical notations (translated via compilers) Example: grossPay = basePay + overTimePay Other high-level languages –FORTRAN Used for scientific and engineering applications –COBOL Used to manipulate large amounts of data

 2001 Prentice Hall, Inc. All rights reserved. 1.7 Structured Programming Structured programming –Disciplined approach to writing programs –Clear, easy to test and debug and easy to modify Development of programming languages –Pascal Designed for teaching structured programming –C Developed for writing systems software and compilers –Ada Developed to meet the needs of the Department of Defense Multitasking

 2001 Prentice Hall, Inc. All rights reserved. 1.8 Object-Oriented Programming Software reuse Programs more understandable and easier to maintain History –Dates back to at least mid 1960s –Development of C++ Added capabilities to create and manipulate objects –Development of Java in early 1990s –Completely object-oriented language

 2001 Prentice Hall, Inc. All rights reserved. 1.9 Hardware Trends Improving technologies –Internet community thrives on improvements of Hardware Software Communications –Cost of products and services Consistently dropping over the decades –Computer capacity and speed Doubles every two years (on average) –Microprocessor chip Laid groundwork in late 1970s and 1980s for productivity improvements of the 1990s

 2001 Prentice Hall, Inc. All rights reserved History of the Internet The Internet enables –Quick and easy communication via –International networking of computers Packet switching –The transfer of digital data via small packets –Allows multiple users to send and receive data simultaneously No centralized control –If one part of the Internet fails, other parts can still operate Bandwidth –Information carrying capacity of communications lines

 2001 Prentice Hall, Inc. All rights reserved History of the World Wide Web WWW –Allows computer users to locate and view multimedia- based documents –Introduced in 1990 by Tim Berners-Lee Internet today –Mixes computing and communications technologies –Makes information constantly and instantly available to anyone with a connection

 2001 Prentice Hall, Inc. All rights reserved History of Perl Developed by Larry Wall in 1987 –Aimed to integrate features of the UNIX languages awk and sed with framework provided by shell Gained support in open-source community Versions of Perl –Perl 3 Adopted GNU General Public License –Perl 4 Adopted Artistic License to attract more users –Perl 5 Major reorganization of Perl language

 2001 Prentice Hall, Inc. All rights reserved History of Perl –Perl 6 Development announced on July 18, 2000 Will be a complete rewrite of internals and externals of Perl

 2001 Prentice Hall, Inc. All rights reserved Perl Library Perl modules –Reusable pieces of software –Defined in library files ending in.pm –Primary distribution center is the Comprehensive Perl Archive Network (CPAN)

 2001 Prentice Hall, Inc. All rights reserved General Notes About Perl and This Book Perl approach to programming –Qualities of a good programmer Laziness –Reusable code Impatience –Functional programs Hubris –Easy to understand code –Programs can be written in many different ways –Highly portable