Practical Introduction to Computer Architecture

649 Pages·2009·9.45 MB·English

by  Daniel Page

Texts in Computer Science
Editors
DavidGries
FredB.Schneider
Forfurthervolumes:
http://www.springer.com/series/3191
Daniel Page
A Practical Introduction to
Computer Architecture
123
Dr.DanielPage
UniversityofBristol
Dept.ComputerScience
Room3.10,MerchantVenturersBuilding
WoodlandRoad,Bristol
UnitedKingdom,BS81UB
[email protected]
SeriesEditors
DavidGries FredB.Schneider
DepartmentofComputerScience DepartmentofComputerScience
UpsonHall UpsonHall
CornellUniversity CornellUniversity
Ithaca,NY14853-7501,USA Ithaca,NY14853-7501,USA
ISBN 978-1-84882-255-9 e-ISBN 978-1-84882-256-6
DOI 10.1007/978-1-84882-256-6
SpringerDordrechtHeidelbergLondonNewYork
BritishLibraryCataloguinginPublicationData
AcataloguerecordforthisbookisavailablefromtheBritishLibrary
LibraryofCongressControlNumber:2009922086
(cid:2)c Springer-VerlagLondonLimited2009
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as
permittedundertheCopyright,DesignsandPatentsAct1988,thispublicationmayonlybereproduced,
stored or transmitted, in any form or by any means, with the prior permission in writing of the
publishers,orinthecaseofreprographicreproductioninaccordancewiththetermsoflicensesissuedby
theCopyrightLicensingAgency.Enquiriesconcerningreproductionoutsidethosetermsshouldbesent
tothepublishers.
Theuseofregisterednames,trademarks,etc.,inthispublicationdoesnotimply,evenintheabsenceofa
specificstatement,thatsuchnamesareexemptfromtherelevantlawsandregulationsandthereforefree
forgeneraluse.
Thepublishermakesnorepresentation,expressorimplied,withregardtotheaccuracyoftheinformation
containedinthisbookandcannotacceptanylegalresponsibilityorliabilityforanyerrorsoromissions
thatmaybemade.
Printedonacid-freepaper
SpringerispartofSpringerScience+BusinessMedia(www.springer.com)
ToKate♥
Foreword
It is a great pleasure to write a preface to this book. In my view, the content is
uniqueinthatitblendstraditionalteachingapproacheswiththeuseofmathematics
and a mainstream Hardware Design Language (HDL) as formalisms to describe
key concepts. The book keeps the “machine” separate from the “application” by
strictlyfollowingabottom-upapproach:itstartswithtransistorsandlogicgatesand
onlyintroducesassemblylanguageprogramsoncetheirexecutionbyaprocessoris
clearlydefined.
Using a HDL, Verilog in this case, rather than static circuit diagrams is a big
deviation from traditional books on computer architecture. Static circuit diagrams
cannotbeexploredinahands-onwaylikethecorrespondingVerilogmodelcan.In
ordertounderstandwhyIconsiderthisshiftsoimportant,onemustconsiderhow
computer architecture, a subject that has been studied for more than 50 years, has
evolved.
Inthepioneeringdayscomputerswereconstructedbyhand.Anentirecomputer
could (just about) be described by drawing a circuit diagram. Initially, such dia-
grams consisted mostly of analogue components before later moving toward dig-
ital logic gates. The advent of digital electronics led to more complex cells, such
ashalf-adders,flip-flops,anddecodersbeingrecognisedasusefulbuildingblocks.
However, miniaturisation of devices and hence computers has led to the design of
singlecircuitscontainingmillionsorevenbillionsofcomponents.Asaresult,hand-
lay-out isonlyused forspecific modules, and circuitdiagrams arelessuseful asa
mechanismfordescribingfunctionalityforrealcircuits.
Instead, two formalisms are used in industry: HDLs and mathematics. A HDL
allows us to tell the component-layout and simulation tools how we would like to
implement our circuit; mathematics tells us what the circuit ought to do. In order
toverifywhetherthecircuitdoeswhatwewantitto,wecan(partlymechanically)
compare the mathematical description with the HDL description. This represents
increased use of abstraction to cope with complexity, and an engineer can now be
productivebysimplyunderstandingandusinghigh-levelcircuitdesign(e.g.,multi-
plierdesignorpipelinedprocessors)andformalisms(e.g.,HDLsandmathematics).
vii
viii Foreword
Circuitdiagramsarestillusedinthedesignflow,butmostlytosketchthephysical
layout,inordertopredictwhetheracircuitcanbelaidoutsensibly.
Dealingwithgapsinunderstandingbetweensuchawiderangeofconceptsand
techniques is often off-putting for people new to the subject. The best way to ap-
proachtheproblemisbyplacingitwithinapracticalcontextthatenablesstudents
toexperimentwithideasanddiscoverthemselvestheadvantagesanddisadvantages
ofaparticulartechnique.
Inthisbook,Dandoesjustthatbygivinganexcellentoverviewofkeyconcepts
andanintroductiontoformalismswithwhichtheycanbeexplored.Ihopethisbook
willinspiremanyreaderstofollowacareerinthisfascinatingsubject.
HenkMuller.
PrincipalTechnologist,XMOS.
Preface
Intheorythereisnodifferencebetweentheoryandpractice.Inpracticethereis.
–L.P.“Yogi”Berra
Overview
In my (limited) experience, and although there are a number of genuinely excel-
lent textbooks on the subject, two main challenges exist in relation to delivery of
Universityleveltaughtmodulesincomputerarchitecture:
1. Such modules are often regarded as unpopular and irrelevant by students who
have not been exposed to the subject before, and who view a computer system
fromtheapplicationslevel.Thisiscompoundedbytheprevalenceoftechnolo-
gies such as Java which place a further layer between the student and actual
computerhardware.Inshort,andnomatterhowonetriestopersuadethemoth-
erwise,studentsoftenseenopointinlearningabouttheinternalsofacomputer
systembecausetheycannotseethebenefit.
2. Conventionaltextbooksteachthesubjectinadifferentwaythaninothermodules
studentsareexposedtoatthesametime.Forexample,conventionalwisdomsays
that one cannot “teach” programming, one has to “do” programming in order
to learn. This is in stark contrast to textbooks on computer architecture where
students are often forced to learn in a more theoretical way, learning by taking
factsforgrantedratherthanexperimentingtoarriveattheirownconclusions.For
example,becauseofthedifficultyinworkingwithlargelogicdesignsonpaper,
anypracticalworkisoftenlimitedandhencedetachedfromthemorechallenging
content.
I would argue that this is a shame: computer architecture represents a broad spec-
trum of fundamental and exciting topics that underpin computer science in gen-
eral.Asidefromthetechnicalchallengesandsenseofachievementthatstemfrom
ix
x Preface
understanding exactly how high-level programs are actually executed on devices
builtfromsimplebuildingblocks,historicaldevelopmentsincomputerarchitecture
neatlycaptureandexplainmanydesigndecisionsthathaveshapedalandscapewe
nowtakeforgranted.TherepresentationofstringsinCisagreatexample:thenull-
terminated ASCIIZ approach was not adopted for any real reason other than the
PDP-7computerincludedinstructionsidealforprocessingstringsinthisform,and
yet we still live with this decision years after the PDP-7 became obsolete. Seem-
ingly frivolous anecdotes and examples like this are increasingly being consigned
to history whereas from an Engineering perspective, one would like to learn and
understandpreviousapproachessoastopotentiallyimproveinthefuture.
International experts regularly debate tools and techniques for delivering
University-levelmodulesincomputerarchitecture;theWorkshoponComputerAr-
chitectureEducation(WCAE),currentlyheldinconjunctionwiththeInternational
SymposiumonComputerArchitecture(ISCA),isthepremierresearchconference
inthisarea.Thisbookrepresentsanattemptattranslatingmypersonalphilosophy,
that theoretical concepts should be accessible for practical experimentation, into a
formsuitableforuseinsuchmodules.Putsimply,Iseecomputerarchitectureasa
subjectinwhich“gettingthingsdone”isparamount;theabilitytounderstandtrade-
offs before selecting between and implementing well considered design options is
oftenasimportantasthestudyofthoseoptionsatamoretheoreticallevel.Thisfo-
cusisunderlinedbythebooksub-title:a“practical”approachistheaimthroughout.
Toenablethis,akeyfeatureofthisbookisinclusionanduseofahardwaredescrip-
tion language (i.e., Verilog), and a concrete processor (i.e., MIPS32) as practical
vehiclesformodellingandexperimentingwithdigitallogicandprocessordesign.
TargetAudience
Thecontentisorganisedintothreepartswhichcontainatotalofthirteencorechap-
ters. Although some slight disagreement about inclusion of specific topics is in-
evitable,thechaptersrepresentacompromisebetweenmyinformalopinion,inter-
estsandexperience,andmoreformalcurriculumguidelinessuchasthatdeveloped
bytheUKQualityAssuranceAgency(QAA):
http://www.qaa.ac.uk/
Ofcourse,internationalequivalentsexist;examplesincludethosedevelopedjointly
bytheIEEEandACM,leadingprofessionalbodieswithinthisdomain:
http://www.computer.org/curriculum/
The general aim of this book is to cover topics every computer science student
should have at least a basic grasp of, and equip said students with enough knowl-
edgetoreadandunderstandmoreadvancedtextbooks.Inthisrespect,thecoretar-
getaudienceisfirst-yearUndergraduatestudentswitharudimentaryknowledgeof
Preface xi
programminginC.Moregenerally,thebookcontentispitchedatalevelwhichsat-
isfies most of the demands that have resulted from our degree programmes at the
UniversityofBristol.Inparticular,themoreadvancedmaterialhasprovedusefulas
a bridge toward, or in support of, more specialised textbooks that cover later-year
UndergraduateandPostgraduatemodules.
Organisation
The book chapters aredescribed briefly below. Veryroughly thethree partsof the
bookcanbeviewedassomewhatself-contained,representingthreelayersorlevels
ofabstraction:thedigitallogiclayer,theinstructionsetandmicro-architecture
layer,andthehardware/softwareinterface.Part1dealswithbasictoolsandtech-
niqueswhichunderpintherestofthebook:
Chapter1 Introducesthetheoreticalbackgroundincludinglogic,sets,andnum-
berrepresentation.
Chapter2 Usesthetheorydevelopedinthepreviouschaptertodescribetheba-
sicsofdigitallogicincludinglogicgatesandtheirconstructionusingtransistors,
combinatorialandclockedcircuitsandtheiroptimisation.
Chapter3 Asameansofrealisingthedigitallogicdesignspresentedinthepre-
vious chapter, Verilog is presented in an introductory manner; this content is
writtenwithareaderwhoisaproficientCprogrammerinmind.
Part2dealswiththebroadtopicofprocessordesignandimplementation.Thecon-
tenttakesastep-by-stepapproach,startingwithafunctionaldescriptionofacom-
puter processor and gradually expanding on the details, issues and techniques that
haveresultedinmodern,high-performanceprocessordesigns:
Chapter4 Thefirststepinintroducingthedesignofprocessors(asanextension
tothestudyofgeneralcircuits)istotrackhistoricaldevelopmentsandusethem
asameanstoexplaincentralconceptssuchasthefetch-decode-executecycle.
Chapter5 Once the core concepts are introduced, a concrete realisation in the
formofMIPS32isdiscussed;thisdiscussionincludesdetailssuchasaddressing
modesandinstructionencodingforexample.
Chapter6 This chapter outlines some basic methods for evaluating processors
in terms of various metrics which can be used to defined quality, focusing on
performanceinparticular.
Chapter7 Asavitalcomponentinanyprocessor,thedesignofefficientcircuits
forarithmetic(e.g.,additionandmultiplication)isintroducedanddemonstrated
usingVerilog.
Chapter8 Inthesamewayasarithmetic,thedesignofefficientcomponentsin
thememoryhierarchyisintroducedanddemonstratedusingVerilog.
Chapter9 Finally, a number of more advanced topics in processor design are
investigatedincludingapproachessuchassuperscalarandvectorprocessors.