THE DESIGN PHILOSOPHY OF A SMALL ELECTRONIC AUTOMATIC DIGITAL COMPUTER Thesis Presented for the Degree of Doctor of Philosophy By Paiil A.V. Thomas, B.Sc. (Eng.) June. 1961 ProQuest Number: 13850774 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13850774 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 CONTENTS Page No. 1. Introduction 1 2. The History of Automatic Digital Computers 3 2.1 The Mechanical Era 3 2.1.1 Charles Babbage and his Difference Engine U 2.1.2 Babbage's Analytical Engine 6 2.2 'Die Electromechanical Era 9 2.3 The Electronic Era 12 3. Computer Basic Units 20 3*1 Storage Elements 21 3.2 Main Storage 22 3.2.1 The Ultrasonic Delay line Store 22 3.2.2 Ihe Magnetic Drum Store 23 3.2.3 The Magnetic Core Store 23 3.2.U Magnetic Storage Cost 2h 3.3 Temporary Storage 2S> 3 .3 .1 Main S tore 'fypes 26 3.3.2 Bistable Units 27 3 .I* Control Gates 30 Page No, U• Valve Computer 32 U.l General Requirements 32 U.2 Word Length 33 14. 2 .1 Number Form 33 U .2.2 In stru c tio n Form 3U U.3 Size or the Main Store 37 I4.I4 The Arithmetic Unit 38 U.5 Operation Timing 39 I4.6 Input-Output Facilities I 4I U.7 Final Arrangements U2 5. Transistor Computer. General Considerations U5 5*1 Historical Development U5 5.2 Size or Computer 50 5.3 Speed of Operation 5U 5.3.1 Minimum Timing of Operations 55 5.U Order Code £8 5. U.l Multiplication 58 5.U.2 Division 61 5.U.3 Shift Operations 63 5.U.U Normalise Operation 63 5.U.5 Input-Output Operations 65 5.U.6 Modify Orders 67 5 .U.7 Jump In stru c tio n s 67 5.U.8 Stops 68 5.5 Initial Orders 69 Page No. 6. Transistor Computer* Logical Design, 71 6 .1 General 71 6.2 Basic Timing 71 6.3 Basic Instruction Period 73 6.U Basic Operation Period 7k 6,5 L-Register Operations 77 6,6 Multipli cation 78 6.7 D ivision 82 6.8 Shirt Operations 8U 6.9 Normalise Operation 86 6.10 Input and Output Operations 91 6.11 Modify Orders 96 6.12 Jump In stru c tio n s 97 6.13 Starting Procedure 98 6.11* Stopping Precautions 100 6.1U.1 Causes of Stopping 100 Transistor Computer. Engineering Design 101* 7.1 Gates 10h 7.2 Logical Units 107 7.3 Bistable Unit 109 7.3.1 Steady State Stability 111 7.3.2 Transient Analysis 112 7.3.3 Transient Analysis Experiments 117 7.3.U Effects of the Circuit Parameters 119 7.3.5 Transistor Parameters 123 7.3.6 Conclusions 225 Page No. 7.1* Counters 126 7*5 R eg isters 126 7*6 Main S tore 229 7.7 Initial Order Store 130 8. Conclusions 332 9 . Bibliography 136 10. Appendices: 11*3 Appendix I - Glossary 11*3 Appendix I I - Symbols 150 Appendix III — Valve Computer Order Code 152 Appendix IV - Transistor Computer Order Code 151* Appendix V - Initial Orders l£9 Appendix VI - Dialling Subroutine 166 Appendix VII - Reprint of Reference 56 168 1 1* Introduction The Thesis being submitted is an account of the development of a small electronic digital computer which began during the summer of 1956, after the Author had attended the Convention on D ig ita l Computer Techniques (April 1956) held under the auspices Of the Institution of Electrical Ehgineers* At this meeting i t was suggested, during one of the many discussions, that one of th e problems was to in stil an understanding of digital computers into the engineering world, starting right back at the students in the Universities and Technical Colleges* With these thoughts in mind, the Author approached the late Professor B* Hague with the idea or developing simple analogue and digital computers, primarily xor teaching students both how to use them and also, in the case of studmts of electrical engineering, their basic design, Ihe idea was received enthusiastically and a Grant was made av a ila b le to develop the two machines* Though the work: was begun in 195©, whoa a rough scheme was drafted in order to obtain a Grant, the sain part oi the work was not started until two years later, the intervening period having been devoted to the development of the analogue computer. this, in fact, proved to be a fortunate 'decision, as it enabled the Author to take advantage ci rapfaiy falling prices of transistors during the two years in stead of using thendumic valves, as originally intended, •;"5he 2 - The Thesis concerns itself with the development of the Digital Computer only, in particular with the special problem of providing a flexible machine as comparable as possible with modern design and techniques and yet keeping the cost to a low value. In order to do this, in the final design, considerable time was devoted to the overall logical design and to analytical and experimental investigation of some of the basic units in order to achieve a maximum operating speed with essaitially low frequency components, Die Author wishes to acknowledge the support and encouragement given to him by the late Professor B. Hague and to thank Dr. A.J. Small for permission to use the facilities in the Electrical Ehgineering Laboratories, He also wishes to thank Dr. D,C. Gilles and his staff in the Computing Laboratory for their help, and Messrs. Barr & Stroud Ltd. for their help, in particular with regard to the construction of the final machine. - 3 - 2. History of Automatic Digital Computers 2.1 The Mechanical Era The earliest known form of digital calculator was the Abacus which dates back several thousands of years, though s till in use in Japan today and, it is said, was introduced into Europe about a thousand years ago by Gerber, who later became Pope Sylvester This was followed considerably later (about 1630) by ttNapier,s Bones11 as they were called, which were a system of numbered rods used as an aid to computation devised by John Napier of Napierian Logarithm fame^. The first mechanised digital calculator was not built for a further 12 years, when Blaise Pascal produced his calculating machine, which incorporated ten position wheels for each decade and, more important, included automatic carry from one decade to the next^. Finally, in 1673, Leibnitz produced a machine in which multiplication was automatically carried out by the process of „ bU continued addition”. However, none of th ese machines was autom atic and, though there was considerable development of these machines in the form of desk calculators, as they have come to be called, there was no further /development A References to individual articles are given by a number whereas references to a book are given by a book reference letter followed by the relevant page number; thus reference BU refers to page U of book reference B (see bibliography). - it - development towards an automatic machine until the 19th century, when Charles Babbage, a Cambridge mathematician, laid down the principles or the modem automatic calculating machines when he designed, but unfortunately never built, his "Analytical Ehgine". It seems only fair, therefore, to devote a few lines to this genius, without whom the modem computers might not eadLst. 2.1.1 Charles Babbage and his Difference Engine Charles Babbage was bom in Devonshire in 1792 and went up to Cambridge in 1810 to study mathematics. However, he was so much ahead of his time that he eventually refused to take the Mathematics Tripos, though this did not prevent him from eventually becoming the Lucasian P rofessor of Mathematics®*^ (1828 - 1839) • In the intervening years he, together with George Peacock and John Herschel, founded the Analytical Society and it was in the Society Booms that Babbage, in 1812, first produced his ideas for a computing machine. At the time, the French Government were producing new tables of logarithms, the bulk of the labour force, numbering about 80, carrying out the actual calculations of interpolation involving the operations of addition and subtraction. Babbage proposed to replace these human computers by a machine, the Difference Engine, for which a very able account is given in the "Edinburgh Review" of July In 1822 he constructed and demonstrated a small working model, which would tabulate to 8 decimals, a function whose second differences were / constant - 5> - Wk ^ . BB7 , constant and produced figures at the rate of kh a minute • This was received with such enthusiasm that the British Government agreed to give financial support to the construction of a larger machine, the Difference Ehgine; this machine was to work to an accuracy of 20 decimals and sixth-order differences and also to print out automatically the results to avoid errors of transcription, Die machine was never completed, due mainly to the lack of precision equipment to manufacture component parts and the work was stopped in 1833, the Government finally abandoning the project in 18142, Die most important problem that Babbage solved in this design was a method of simultaneous operation of all "carries11, thereby speeding up the propagation of "carry over" in addition from one end of a twenty-digit number to the other, changing a whole BIO series of nines to zeros, - a slow process • The modem equivalent to this is in use today in all parallel computers.