Sylvia Langfield and Dave Duddell Cambridge International ...

[Pages:7]Cambridge University Press 978-1-107-54673-8 ? Cambridge International AS and A Level Computer Science Sylvia Langfield Dave Duddell Frontmatter More information

Sylvia Langfield and Dave Duddell

Cambridge International AS and A level

Computer Science

Coursebook

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Cambridge University Press 978-1-107-54673-8 ? Cambridge International AS and A Level Computer Science Sylvia Langfield Dave Duddell Frontmatter More information

CAMBRIDGE

UNIVERSITY PRESS

University Printing House, Cambridge CB2 8BS, United Kingdom

Cambridge University Press is part of the University of Cambridge.

It furthers the University's mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence.



Information on this title: education.

? Cambridge University Press 2015

This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press.

First published 2015

Printed in the United Kingdom by Latimer Trend

A catalogue record for this publication is available from the British Library

ISBN 978-1-107-54673-8 Paperback

Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. ........................................................................................................................................................................................... NOTICE TO TEACHERS IN THE UK It is illegal to reproduce any part of this work in material form (including photocopying and electronic storage) except under the following circumstances: (i) where you are abiding by a licence granted to your school or institution by the

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The past paper questions on pages 107-108 and 316 are taken from the 9608 Specimen papers 1 and 3 respectively and are reproduced with the permission of Cambridge International Examinations.

All other examination-style questions and comments that appear in this book were written by the authors.

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Cambridge University Press 978-1-107-54673-8 ? Cambridge International AS and A Level Computer Science Sylvia Langfield Dave Duddell Frontmatter More information

Contents

Contents

Introduction

PART 1 THEORY FUNDAMENTALS

Chapter 1 Information representation Chapter 2 Communication and Internet technologies Chapter 3 Hardware Chapter 4 Logic gates and logic circuits Chapter 5 Processor fundamentals Chapter 6 Assembly language programming Chapter 7 System software Chapter 8 Data security, privacy and integrity Chapter 9 Ethics and ownership Chapter 10 Database and data modelling

PART 2 FUNDAMENTAL PROBLEMSOLVING AND PROGRAMMING SKILLS

Chapter 11 Algorithm design and problem solving Chapter 12 Stepwise refinement and structure charts Chapter 13 Programming and data representation Chapter 14 Structured programming Chapter 15 Software development

PART 3 ADVANCED THEORY

Chapter 16 Data representation Chapter 17 Communication and Internet technologies Chapter 18 Boolean algebra and logic circuits Chapter 19 Processor and computer architecture Chapter 20 System software Chapter 21 Security Chapter 22 Monitoring and control systems

v

2 18 36 49 59 69 78 88 99 109

iii

125 155 176 212 228

246 258 270 282 287 303 310

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Cambridge University Press 978-1-107-54673-8 ? Cambridge International AS and A Level Computer Science Sylvia Langfield Dave Duddell Frontmatter More information

Cambridge International AS and A level Computer Science

PART 4 FURTHER PROBLEM-SOLVING AND PROGRAMMING SKILLS

Chapter 23 Computational thinking and problem-solving

317

Chapter 24 Algorithm design methods

337

Chapter 25 Recursion

347

Chapter 26 Further programming

356

Chapter 27 Object-oriented programming (OOP)

368

Chapter 28 Low level programming

394

Chapter 29 Declarative programming

405

Chapter 30 Software development

420

Glossary

430

Index

434

Acknowledgements

442

iv

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Cambridge University Press 978-1-107-54673-8 ? Cambridge International AS and A Level Computer Science Sylvia Langfield Dave Duddell Frontmatter More information

Introduction

This full-colour, illustrated textbook has been written by experienced authors specifically for the Cambridge International AS and A Level Computer Science syllabus (9608). The presentation of the chapters in this book reflects the content of the syllabus: ? The book is divided into four parts, each of which is closely matched to the corresponding

part of the syllabus. ? Each chapter defines a set of learning objectives which closely match the learning

objectives set out in the syllabus. ? The syllabus defines two assessment objectives: A01 Knowledge with understanding and

A02 Skills. Papers 1 and 3 have a major focus on A01 and Papers 2 and 4 have a major focus on A02. The chapters in Parts 1 and 3 have been written with emphasis on the promotion of knowledge and understanding. The chapters in Parts 2 and 4 have been written with an emphasis on skill development. The chapters in Parts 1 and 3 have a narrative. We would encourage students to read the whole chapter first before going back to revisit the individual sections. The chapters in Parts 2 and 4 contain many more tasks. We would encourage students to approach these chapters step-by-step. Whenever a task is presented, this should be carried out before progressing further. In particular, Chapter 11 (Algorithm design and problem-solving) may be worked through in parallel with Chapter 13 (Programming and data representation). For example, Task 13.03 is based on Worked Example 11.03. After studying this worked example, students may wish to cover the first part of Chapter 13 and write the program for Task 13.03. This will give the student the opportunity to test their understanding of an algorithm by implementing it in their chosen programming language. Then further study of Chapter 11 is recommended before attempting further tasks in Chapter 13.

Introduction

v

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Cambridge University Press 978-1-107-54673-8 ? Cambridge International AS and A Level Computer Science Sylvia Langfield Dave Duddell Frontmatter More information

Cambridge International AS and A level Computer Science

How to use this book: a guided tour

Chapter ? each chapter begins with a short list of the learning objectives and concepts that are explained in it.

2

Chapter 1 Information Representation

Learning objectives

By the end of this chapter you should be able to:

systems show understanding of, and be able to represent,

character data in its internal binary form show understanding of how data for a bitmapped or

vector graphic image is encoded

show understanding of how sound is represented and encoded

show understanding of the characteristics of video streams show understanding of how digital data can be

compressed.

TASK 1.01 Convert the denary number 374 into a hexadecimal number. Convert the hexadecimal number 3A2C to a denary number.

Key Term ? clear and straightforward explanations of the most important terms in each chapter.

KEY TERMS Byte: a group of eight bits treated as a single unit

Task ? exercises for the student to test their skills.

Question ? questions for the student to test their knowledge and understanding.

Discussion Point ? discussion points intended for class discussion.

Question: Construct a partial drawing list for the graphic shown in figure 1.06. You can take measurements from the image and use the bottom le corner of the box as the origin of a

vi

coordinate system. You can invent your own format for the drawing list.

Discussion Point What is the two's complement of the binary value 1000? Are you surprised by this?

Extension Question: Graphic files can be stored in a number of formats. For example, JPEG, GIF, PNG and TIFF are just a few of the possibilities. What compression techniques, if any, do these use?

Extension Question ? extended questions for consideration of more advanced aspects or topics beyond the immediate scope of the Cambridge International AS and A Level syllabus.

Tip ? quick notes to highlight key facts and important points.

Worked Example ? step-by-step examples of solving problems or implementing specific techniques.

! TIP For multiples of bytes, the terminology used has recently changed. Traditionally, computer scientists have used the terminology kilobyte, megabyte, gigabyte etc. in a way that conflicted with the definition of these prefixes established by the International System of Units (SI). Following the SI convention, one kilobyte would represent 1000 bytes. Computer scientists have used one kilobyte to represent 1024 bytes. There have been a number of variations on how this was written, for example Kbyte, KB or kB but the basic contradiction remained. In order to resolve this unsatisfactory situation, the International Electrotechnical Commission (IEC) in 1998 proposed a new set of definitions for such quantities. 1024 bytes is now identified as one kibibyte where the kibi can be considered as representing kilobinary. This proposal has been accepted by other international standards bodies.

Converting a negative number expressed in two's complement form to the corresponding denary number.

Consider the two's complement binary number 10110001.

Method 1. Convert to the corresponding positive binary number then find the denary value

Converting to two's complement leaves unchanged the 1 in the least significant bit position then changes all of the remaining bits to produce 01001111.

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Extension Question 1.01

Graphic files can be stored in a number of formats. For example, JPEG, GIF, PNG and TIFF are

Cambridge UjunstivaefreswitoyfPthreespsossibilities. What compression techniques, if any, do these use? 9Sy7l8v-i1a-1L0a7n-g5If4fiet6hl7de3iD-m8aav?geeCDcaoumddbidnregildlfoger aInvitdeernoaistitoonbael AcoSmapnrdesAseLde,voenleCaopmpprouatcehr iSsctioentaccekle the spatial Frontmatterredundancy in individual frames using techniques applicable to an image file. However, this More informisautniolinkely to be an efficient technique because, in general, one frame is very similar to the

preceding one. It will be more effective to tackle this temporal redundancy by changing the

frame by frame coding to one which mainly records differences between adjacent frames.

A video contains images and sound but these do not go to the same part of any receiving and displaying system. Clearly the audio and visual parts of a video must be handled independently but in a way that guarantees synchronisation. The solution to this is to package the audio and visual components in what is known as a multimedia container format. This concept is currently being developed by several different organisations or companies. The use is not restricted to

one vidSeoufmile mandaornye sound file. Rather, one multimedia container file will have many audio

and video streams plus other streams, perhaps for subtitles or chapter headings.

A binary code or a binary number can be documented as a hexadecimal number.

Internal coding of signed integers is usually based on a two's complement representation.

BCD is a convenient coding scheme for single denary digits.

ASCII and Unicode are standardised coding schemes for text characters.

Summary An image can be stored either in a vector graphic file or in a bitmap file. An ADC works by sampling a continuous waveform.

A binarLyoscsoledses coormapbreisnsaiornyanlluomwsbaenrocraigninbael fidleotcoubme reencotevdereadsbayhaedxeacdodeecri;mloaslsyncuommbpreers.sion

16

irretrievably loses some information.

Internal coding of signed integers is usually based on a two's complement representation.

BCD is a convenient coding scheme for single denary digits.

ASCII and Unicode are standardised coding schemes for text characters.

An image can be stored either in a vector graphic file or in a bitmap file.

An ADC works by sampling a continuous waveform.

SummarLyosCslhesescckolmisptre?ssaiotnthaleloewnsdanoofreigaincahl fcilheatopbteerrecovered by a decoder; lossy compression to reviewirwrehtraietvtahbelyslotusedsesnotmheainsfolermarantieodn..

vii

Exam-style Questions

1 A file contains binary coding. The following are two successive bytes in the file:

10010101 00110011

a One possibility for the information stored is that the two bytes together represent one unsigned integer binary number.

i Give the denary number corresponding to this. Show your working.

[2]

ii Give the hexadecimal number corresponding to this. Show your working.

[2]

b Give one example of when a hexadecimal representation is used.

[1]

Exam-style Questions ? Exam-style questions for the student to test their skills, knowledge and understanding at the end of each chapter

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