Introduction to Windows as a Platform.docx

Introduction to Windows as a Platform.docx

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IntroductiontoWindowsasaPlatform

VisualStudioExpress:

IntroductiontoWindowsasaPlatform

Author:

RichTebb

Company:

ContentMasterLtd

Introduction

TheVisualStudioExpressEditionsfamilyprovidesafree,lightweight,andeasy-to-learnsuiteofprogrammingtoolsthatareaimedatthehobbyist,novice,andstudentdeveloper.Manypeopleinthiscategorywillnothavehadanyformaltrainingincomputerscience,andindeedtheymaynothaveanyprogrammingexperienceatall.Ifyoufallintothiscategory,don’tworry–thisguideisforyou!

Thisbeginner’sguideisdesignedforpeoplewithlittleornopriorknowledgeofcomputerprogramming,whowanttocreatecomputerprogramswiththeVisualStudioExpresstools.Ifyoualreadyhavesignificantprogrammingexperience,thenyouwillprobablynothavemuchtolearnfromthisarticle.

So,whatwillyoulearnbyreadingthroughthisguide?

Well,ifyouwanttowriteaprogramthatyoucanrunonyourMicrosoftWindowscomputer,thisguidewillintroduceyoutothefundamentalconceptsthatwillhelpyouunderstandhowtodojustthat.Youwilllearntheanswertoquestionssuchas:

∙Howdoesacomputerwork?

∙What’sthedifferencebetweenhardwareandsoftware?

∙What’sanOperatingSystem?

∙Howdoesacomputerrunmyprogram?

∙Whatarethecomponentpartsofaprogram?

ThepurposeofthisguideistohelpyouunderstandtheenvironmentinwhichaMicrosoftWindowsprogramruns.Thewaythataprogramworksisaffectedbymanyfactorsincludingthecomputerthatitrunson,theoperatingsystem,andthewaythatpeoplewillusetheprogram.Theenvironmentofacomputerprogramiscalleditsplatform.Whenyouunderstandtheprogrammingenvironment,youwillbeabletoappreciatehowthecomputerinterpretsyourprograms,andasaresult,learningtoprogramwillbecomeeasierandultimatelyyou’llwritebetterprograms.

ThisguidedescribestheMicrosoftWindowsplatformasaprogrammingenvironment.ItappliestoprogramsthatrunonWindowsandareusedbypeoplethatrunMicrosoftWindows–thesearecalledWindowsapplications.Ifyouwanttowriteanapplicationthatpeoplewillaccessbyusingthroughtheirbrowser,thenyouneedtocreateaWebapplication,notaWindowsapplication.Inthatcase,youshouldreadthecompanionguide“IntroductiontoWebasaplatform”,whichprovidesinformationabouttheWorldWideWebasanapplicationplatform.

HowComputersWork

Althoughcomputersconsistofadvancedtechnologicalcomponents,thebasicwayacomputeroperatesisverysimple,andhaschangedverylittlesincetheinventionofelectroniccomputersinthemiddleofthetwentiethcentury.Acomputercontainsthreemainfunctionalareas:

∙Input/Output.Thisreferstoanydeviceattachedtothecomputerthatprovidesameansofinteractionorcommunicationbetweenthecomputerandthe‘outsideworld’（fromthecomputer’sperspective）.Examplesofinputdevicesincludethekeyboard,mouse,andjoystick.Examplesofoutputdevicesincludethemonitor,printerandsoundcard.

∙Memory.Thisisthepartofthecomputerthatprovidesinformationstorage.Acomputer’smemoryisdividedintomanythousandsofsmallunitscalledbytes.Allthedatathatacomputermanagesisstoredasoneormorebytes.Youcanimaginethesebytesasslotsorpigeonholes,eachwithitsownmemorylocationoraddressthatthecomputerusestofetchandstoredata,similartoaroomfullofPostOfficeboxes.Each‘box’orbytecontainsanumberthatthecomputercanprocess.

∙CentralProcessingUnit.TheCentralProcessingUnit（CPU）isthe‘brain’ofthecomputer,whichperformsallcalculationsandco-ordinatestheoperationofthememoryandinput/outputdevices.

TheInstructionCycle

AcomputeroperatesbycopyingbytesfromthememoryoraninputdeviceontotheCPU,performingsomecalculationsonthosebytes,andthencopyingtheresultofthecalculationstothememoryoranoutputdevice.Thisprocesscontinuesinacycleasshownbelow:

Forthiscycleofdataprocessingtobeuseful,thecomputerneedstohaveinstructionsthattellitwhattoreadandwrite,andwhichcalculationstoperform.TheseinstructionstelltheCPUwhatmemorylocationtoreadfrom（fetchingdatafrommemory）orwriteto（storingdatatomemory）,andwhichinputoroutputdevicestoaccess.（Lateroninthisarticleyouwillseehowcomputermemorycanholdinformationthatrepresentsexternalentitiessuchasimagesorsound.）

Theinstructionsthatacomputerrunsaresimplynumberslikeanyotherdata,andtheyarestoredinthecomputer’smemory.TheCPUalwayskeepsaninternalrecordofwhichmemorylocation（address）containsthenextinstructionthatitwillexecute.Whenitcompletesoneinstruction,itreadsthenextinstructionfrommemory,andupdatesitsrecordtopointtotheinstructionafterthat.Afterithasupdateditsrecord,itcanprocesstheinstructionthatithasjustreadfrommemory.

SoacomputerprogramisjustaseriesofbytesthatcontaininstructionsfortheCPU.Whenthecomputerrunstheprogram,itmovessequentiallythroughthesetofinstructionbytes,loadingeachinstructionontotheCPU,performingthatinstruction,andthengoingbacktofetchthenextinstructionontotheCPU.TheprogramitselfdoesnotalwaysneedtotelltheCPUtomovetothenextinstruction–thishappensautomatically.

However,instructionscanalsotelltheCPUtomodifyitsinternalrecordsothatitwillreadthenextinstructionfromadifferentaddress.Theseinstructions,called‘jump’instructions,enablethecomputertoperformdifferentactionsdependingonthecircumstances.Let’shavealookathowinstructionsworkinsideacomputer,bytakingsomeexampleinstructionsandseeinghowthecomputerusesthem.

ThediagramdepictsseveralbytesofcomputermemorythatcontainCPUinstructions（inthelowersection）anddata（intheuppersection）.

Inthelowersectionofmemorydepicted,thenumericalvaluesoftheCPUinstructionsaredisplayedinbluetext.AlongsidethenumericalvalueisamnemonicrepresentationoftheCPUinstructionsinsemi-readabletext.

Startingwiththelowestmemorylocation（atthebottomofthediagram）andreadingupwards,theCPUinstructionstelltheCPUtoperformthefollowingactions:

read[8000]

Readthevaluefromaddress8000intotheCPU.

sub100

Subtract100fromthevalueintheCPU（theresultofthesubtractionreplacesthevaluejustreadintotheCPU）.

cmp121

ComparethecurrentvalueintheCPUto121.

jne+8

IftheCPUvalueisnotequal（jnestandsforJumpNotEqual）,jumpforwardby8bytesfromthecurrentinstruction（toaddress2020）andcontinuebyexecutingtheinstructioncontainedatthatmemorylocation.

IftheCPUvalueisequalto121,thentheCPUwouldnotjump,anditwouldcontinuetoreaditsinstructionsfromthenextsequentialmemorylocation,whichis2016inthisexample.

jmp[2038]

Jumptoaddress2038andcontinuebyexecutingtheinstructioncontainedatthatmemorylocation.

write[8842]

WritethevalueintheCPUtomemorylocation8842.

Phew!

Ittakesquitealeapofimaginationtoseehowallthisnumberprocessingcouldenableacomputertoperformalltheactionsthatweusefromdaytoday,likewordprocessingorbrowsingtheInternet.Hangon–you’rethroughthemostcomplicatedpart,butyoustillneedabitmoreinformationtohelpyoumaketheleap.

Challenge:

Asaquickchallenge,seeifyoucanworkoutwhatwillhappenintheexampleabove.Assumingthatthevalueatmemorylocation8000containsthevalue221,workthroughtheCPUinstructionsandanswerthefollowingquestions:

∙Whatvaluegetswrittentomemorylocation8842?

∙Whatvaluegetswrittentomemorylocation8878?

Youcanfindtheanswersattheendofthisarticle.

InputandOutputDevices

Ifacomputersimplyprocessedinstructionsinmemory,itwouldnotserveanyusefulpurpose.Inordertobeuseful,thecomputerneedstoprovideawaytoenabletheusertoindicatewhatcalculationstoperform,andtodisplaytheresultsofitscalculations–tointeractwiththecomputer.

Interactionwithacomputertakesplacethroughcomponentscalledinput/outputdevices.Forexample,akeyboardisaninputdevice,becausethecomputercanreadfromthekeyboardtoseewhenakeyispressed.Fromthecomputer’sperspective,thekeypressisinformationthatiscomingin.Conversely,amonitorisanoutputdevice,becausethecomputersendsinformationouttothedisplayasaresultofitscalculations.

Youmaywonderhowthecomputercaninteractwiththesedevices,whenallitdoesiscopybytesfromoneplacetoanotherplace.Theansweristhatalltheinputandoutputinformationcanberepresentedasbytes.Forexample,eachkeyonthekeyboardhasitsownnumericvaluesothecomputercanidentifythekeyandstorethenumberinamemorylocation.

Lessobviously,theinformationdisplayedonyourmonitorrightnowisjustaseriesofbytestothecomputer.Eachdot（pixel）onthescreenisrepresentedbysomebytesthatindicatewhatcolortodisplayonthemonitoratthatpixel.

Infact,everythingthatacomputerdisplaysorstoresisasetofbytes,calledadigitalrepresentation–whetheritisaphoto,avideo,asong,orevenawordprocessingdocument.Ifyou’veeverseenthemovieTheMatrix,you’llrecognizetheimageofgreen0’sand1’scascadingdownablackscreen.Thisimageactuallyhassometruthtoit,sinceacomputerseesalldataasrepresentedbynumbers.Thetranslationbetweenwhatacomputerseesandwhatweseeonourmonitorsorasaprintoutisdonebytheinput/outputdevices.

Thejobofthecomputer’sinput/outputdevicesistoperformtheseconversionsbetweenth