Fundamentals of Computer Science

Transcription

1 Fundamentals of Computer Science

2 Macmillan Computer Science Series Consulting Editor Professor F. H. Sumner, University of Manchester S.T. Allworth and R.N. Zobel, Introduction to Real-Time Software Design, second edition Ian 0. Angell, A Practical Introduction to Computer Graphics Ian 0. Angell and Gareth Griffith, High Resolution Graphics Using Fortran 77 R.E. Berry and B.A.E. Meekings, A Book on C G.M. Birtwistle, Discrete Event Modelling on Simula T.B. Boffey, Graph Theory in Operations Research Richard Bornat, Understanding and Writing Compilers J.K. Buckle, Software Configuration Management W.D. Burnham and A.R. Hall, Prolog Programming and Applications J.C. Cluley, Interfacing to Microprocessors Robert Cole, Computer Communications, second edition Derek Coleman, A Structured Programming Approach to Data Andrew J. T. Colin, Fundamentals of Computer Science Andrew J.T. Colin, Programming and Problem-solving in Algo/68 S.M. Deen, Fundamentals of Data Base Systems S.M. Deen, Principles and Practice of Data Base Systems B. T. Den vir, Introduction to Discrete Mathematics for Software Engineering P.M. Dew and K.R. James, Introduction to Numerical Computation in Pascal M.R.M. Dunsmuir and G.J. Davies, Programming the UNIX System K.C.E. Gee, Introduction to Local Area Computer Networks J.B. Gosling, Design of Arithmetic Units for Digital Computers Roger Hutty, Fortran for Students Roger Hutty, Z80 Assembly Language Programming for Students Roland N. Ibbett, The Architecture of High Performance Computers Patrick Jaulent, The Hardware and Software J.M. King and J.P. Pardoe, Program Design Using JSP- A Practical Introduction H. Kopetz, Software Reliability E. V. Krishnamurthy, Introductory Theory of Computer Science V.P. Lane, Security of Computer Based Information Systems Graham Lee, From Hardware to Software: an introduction to computers A.M. Lister, Fundamentals of Operating Systems, third edition G.P. McKeown and V.J. Rayward-Smith, Mathematics for Computing Brian Meek, Fortran, PL/1 and the Algols Barry Morrell and Peter Whittle, CP/M 80 Programmer's Guide Derrick Morris, System Programming Based on the PDP// Pim Oets, MS-DOS and PC-DOS - A Practical Guide Christian Queinnec, LISP W.P. Salman, 0. Tisserand and B. Toulout, FORTH L.E. Scales, Introduction to Non-linear Optimization Peter S. Sell, Expert Systems - A Practical Introduction Colin J. Theaker and Graham R. Brookes, A Practical Course on Operating Systems J-M. Trio, Architecture and Programming M.J. Usher, Information Theory for Information Technologists Colin Walls, Programming Dedicated Microprocessors B.S. Walker, Understanding Microprocessors Peter J.L. Wallis, Portable Programming I.R. Wilson and A.M. Addyman, A Practical Introduction to Pascal- with BS6192, second edition

3 Fundamentals of Computer Science Andrew J. T. Colin Professor of Computer Science, University of Strathclyde M MACMILLAN

4 Andrew J. T. Colin 1980 All rights reserved. No reproduction, copy or transmission of this publication may be made without written permission. No paragraph of this publication may be reproduced, copied or transmitted save with written permission or in accordance with the provisions of the Copyright Act 1956 (as amended). Any person who does any unauthorised act in relation to this publication may be liable to criminal prosecution and civil claims for damages. First published 1980 Reprinted 1982, 1983, 1986 Published by MACMILLAN EDUCATION L TO Houndmills, Basingstoke, Hampshire RG21 2XS and London Companies and representatives throughout the world ISBN ISBN (ebook) DOI / The paperback edition of this book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, resold, hired out, or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser.

5 Contents Preface 1. Information 1.1 The Four Information Revolutions 1.2 Some Properties of Information 1.3 Coding 2. Information Inside Computers 2.1 Representation of Characters 2.2 Representation of Numbers 2.3 External Representations of Binary Numbers 3. The Basic Structure of a Computer 3.1 An Over-all View 3.2 Logic Networks 3.3 The Hydraulic Analogy 3.4 Electronic Circuitry 3.5 Truth Tables 3.6 Conversion between Truth Tables and Logic Networks 3.7 Propagation Time 4. The Implementation of Binary Arithmetic 4.1 Serial and Parallel Transmission of Words 4.2 Addition of Numbers 4.3 Subtraction of Numbers 4.4 The Multiplexer 4.5 Shifting Binary Numbers 4.6 An Arithmetic Unit 5. Sequential Networks 5.1 Storage Elements 5.2 Registers viii

6 5.3 Bus Structures Register Transfer Notation Immediate Access Stores Random Access Memory Read-only Memory Timing Introduction to SNARK 62 7.I The SNARK Computer 7.2 The Basic Structure of the SNARK 7.3 Instructions 7.4 Address Modes 7.5 Input and Output 8. Jump Instructions on SNARK 8.1 Conditional Jumps 8.2 Flow Charts 8.3 Controlled Loops Array Handling on SNARK 9.1 The Internal Format of SNARK Instructions 9.2 Index Modification 9.3 Table Look-up 9.4 Access to Entire Tables 9.5 Table Searching 10. Computers- the Grand Design 10.1 Sequences of Operations 10.2 Variable Sequences 10.3 Design of the SNARK 11. Backing Stores 11.1 Serial Storage 11.2 Cyclic Storage 11.3 Hierarchies of Stores 12. Peripheral Devices 12.1 Peripherals for Human Communication 12.2 Punched Paper 12.3 Links with Mechanical Systems 12.4 Communication

7 Contents vii 13. Software 13.1 S:ymbolic Assemblers 13.2 High-level Languages 13.3 Operating Systems 13.4 The Program library 14. Translators 14.1 Language Definition 14.2 Lexical Analysis 14.3 Syntactic Analysis 14.4 Code Generation 14.5 Compilers and Interpreters 15. The History of Computers IS.1 A Classification of Computers 16. Main-frame Computers 16.1 File Maintenance 16.2 Physical and Engineering Problems 16.3 Operating Systems 17. Minicomputers 17.1 General Applications 17.2 Plant Control 17.3 X-ray Tomography 17.4 Packet Switching 18. Microprocessors 18.1 Toys and Games 18.2 Word Processing 18.3 Microcomputers 18.4 Conclusion Appendix A: SNARK- An Abstract Teaching Machine Appendix B: The SNARK Simulator Program Assignments Sample Solutions Bibliography Index

8 Preface Computer science can be divided into two great streams of knowledge: one is programming, and the other deals with the principles, construction and applications of computer systems. This book is centred on the second stream; it is not primarily about programming, but assumes that the reader is following a parallel course on this key subject. The range of knowledge needed to understand a computer system is large. It includes elementary physics, electronics, information theory, logic design, computer architecture, microcoding, machine code programming, compilers, interpreters, operating systems and a selection of typical applications. Most important of all is an over-all view which reveals how all these different areas can be made to work together in harmony to form an integrated system. Traditional introductory computer science courses tend to consider a selection of these topics in isolation. Thus students may well be taught elementary logic design by one lecturer, assembly code programming by another and a high-level language by a third, but the links between these areas are never explored. The student's impression of the subject is of a few islands of clarity set in a sea of incomprehensible magic. The aim of this book is to dispel the magic by providing a continuous and logically connected survey of the subject. For example, the section on logic design does not stop short at elementary combinatorial functions such as binary addition, but goes on to introduce multiplexers, sequential circuits, and buses. The chapter on over-all computer design does not therefore need to rely on abstractions which have no apparent connection with anything already covered in the course, but can use concepts which are familiar to the student. This continuity of treatment in a first-year course cannot be achieved except at a certain cost. First, the text moves fast, and does not often pause to examine details which are not essential to the main theme. Second, the book traces but a single path across the subject. The aim is to show just one way in which a computer system could be implemented. The route chosen is largely arbitrary, and alternative routes that exist at every stage are simply ignored. Every teacher of computer science will be able to name numerous topics which are given the briefest treatment, or not even mentioned. Nevertheless, the student

9 Preface ix who reads and understands the book will know at least one way to implement a working computer system. His knowledge will not have any conceptual gaps, and he will have a unified framework on which to hang new concepts that he may learn in the future. A computer system is one of the most complex artefacts in existence. The only way to understand it is by a holistic approach. This word, first used by Koestler, describes any hierarchic system in which every component part is itself a system constructed from more elementary components. In computer science, the principle of holism appears at every stage, both in software and hardware, and this book puts it to considerable use. Sometimes, as in describing hardware, the approach is from 'bottom-up'. Some functional unit (say a full adder or a multiplexer) is fully described in terms of its elementary components, then it is notionally sealed in a box with the appropriate number of terminals, and used as an 'elementary' component in a more complex structure such as a parallel adder or arithmetic unit. In software, the design method is more often 'top-down'. The book recommends the use of flow charts in which the portions which are not clearly understood at any stage are drawn as 'clouds'. Later, these clouds are expanded and elaborated, perhaps through several levels, until the entire algorithm can be expressed in elementary terms. The use of structure to describe complex systems is perhaps one of the most important mental tools at our disposal. It is hoped that the integrated approach used in this book will help its readers to become totally familiar with the method, and be able to apply it in their everyday study and work. At the end of the book there are ten 'assignments', each based on the ground covered by one or two chapters. Sample solutions are provided. The three assignments on machine coding assume the use of a simple simulator for the SNARK abstract machine. Appendix B includes the listing of a suitable BASIC program for an 8K Commodore PET 2001 *.The program does not make use of graphics or any other of the special features of this machine, and can easily be adapted to run on other systems. My thanks are due to many people who have made the publication of this book possible: to students and colleagues at the University of Strathclyde, who have read the manuscript, made comments and found errors; to Frank Sumner and Simon Lavington, who gave me constant encouragement and detailed, constructive criticism; to Miss Agnes Wisley who typed the book (parts of it many times over); and above all to my wife and family, who left me undisturbed at times when they had every legitimate claim on my time and attention. Glasgow January, 1980 ANDREWCOUN * A cassette tape of this program can be bought from Commodore Ltd, 360 Euston Road, London,NWl

10 Abbreviations ACC ARPA ASCII BASIC BNF CIR COBOL DEC EBCDIC EMI GPO IBM ICL JCL MAR PET Accumulator Advanced Research Project Agency American Standard Code for Information Interchange Beginners' All-purpose Symbolic Information Code Backus-Naur Form Current Instruction Register Common Business-oriented Language Digital Equipment Corporation Extended Binary Coded Decimal Interchange Code Electrical and Musical Industries Ltd General Post Office International Business Machines Ltd International Computers Ltd Job Description Language Memory Address Register Personal Electronic Transactor