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Unit2TheBasicsofComputerSystem2.1Text2.2ReadingMaterials
2.1Text
TheVonNeumannArchitectureofComputerSystemAllcomputerssharethesamebasicarchitecture,whetheritisamainframeoraPalmPilot.Allhavememory,anI/Osystem,andarithmetic/logicunit,andacontrolunit.ThistypeofarchitectureisnamedVonNeumann’sArchitectureafterthemathematician,JohnVonNeumannwhoconceivedofthedesign.
JohnVonNeumannbeginshis“PreliminaryDiscussion”withabroaddescriptionofthegeneral-purposecomputingmachinecontainingfourbasiccomponents.Theseareknownasrelatingtoarithmetic,memory,control,andconnectionwiththehumanoperator.Inotherwords,thearithmetic/logicalunit(ALU),thememory,thecontrolunit(CU),andtheinput-output(I/O)devicesthatweseeintheclassicalmodelofwhatacomputer“l(fā)ookslike”.VonNeumannArchitectureofComputerSystemisshowninFig2.1.Fig2.1VonNeumannArchitectureofComputerSystem
Memory
ComputerMemoryisthesubsystemthatservesastemporarystorageforallprograminstructionsanddatathatarebeingexecutedbythecomputer.ItistypicallycalledRAM(RandomAccessMemory).Memoryisdividedupintocells,eachcellhavingauniqueaddresssothatthedatacanbefetched.
Arithmetic/logicalunit(ALU)
Thissubsystemistoperformallarithmeticoperationsandcomparisonsforequality.IntheVonNeumann’sarchitecture,thearithmetic/logicalunit(ALU)andtheControlUnit(CU)areseparatecomponents,butinmodernsystemstheyareintegratedintotheprocessor.TheALUhas3sections,theregister,theALUcircuitry,andthepathwaysinbetween.TheregisterisbasicallyastoragecellthatworkslikeRAMandholdstheresultsofthecalculations.ItismushfasterthanRAMandisaddressesdifferently.TheALUcircuitryisthatactuallyperformsthecalculations,anditisdesignedfromAND,OR,andNOTgatesjustasanychip.
ControlUnit(CU)
Thecontrolunitisresponsibleforfetchingthenextprograminstructiontoberunfrommemory,decodeittodeterminewhatneedstobedone,andthenissuethepropercommandtotheALU,memoryandI/Ocontrollerstogetthejobdone.Thesestepsaredonecontinuouslyuntilthelastlineofaprogramisdone,whichisusuallyQUITorSTOP.
Input-output(I/O)devices
Thisisthesubsystemthatallowsthecomputertointeractwithotherdevicesandcommunicatetotheoutsideworld.Italsoisresponsibleforprogramstorage,suchasharddrivecontrol.
Technicalwordsandphrases
memory n.內(nèi)存,存儲器
subsystem n.子系統(tǒng);次要系統(tǒng)
execute vt.實行;執(zhí)行
fetch vt.取來;接來;到達;吸引
processor n.處理器;[電腦]處理程序
register n.寄存器
decode vt.[計][通信]譯碼,解碼
basicarchitecture 基本架構(gòu)
aPalmPilot 一臺掌上電腦
bedividedupinto 被劃分為
ALU(arithmetic/logicunit) 算術(shù)/邏輯單元
CU(controlunit) 控制單元
I/O(input-output)system 輸入/輸出系統(tǒng)
RAM(RandomAccessMemory) 隨機存取存儲器
ANDgates 與門
ORgates 或門
NOTgates 非門
Note:JohnVonNeumann約翰·馮·諾依曼,美籍匈牙利人,開創(chuàng)了現(xiàn)代計算機理論,其體系結(jié)構(gòu)沿用至今,早在20世紀40年代他就已預見到計算機建模和仿真技術(shù)對當代計算機將產(chǎn)生的意義深遠的影響。
2.1.1Exercises
1.PutthePhrasesintoEnglish
(1)人工操作;
(2)唯一的地址;
(3)算數(shù)運算;
(4)寄存器;
(5)任何芯片;
(6)正確的命令。
2.PutthePhrasesintoChinese
(1)general-purposecomputingmachine;
(2)humanoperator;
(3)classicalmodel;
(4)temporarystorage;
(5)programinstructionsanddata;
(6)harddrivecontrol.
3.Translation
(1)Memoryisdividedupintocells,eachcellhavingauniqueaddresssothatthedatacanbefetched.
(2)IntheVonNeumann’sarchitecture,thearithmetic/logicalunit(ALU)andtheControlUnit(CU)areseparatecomponents,butinmodernsystemstheyareintegratedintotheprocessor.
(3)Thecontrolunitisresponsibleforfetchingthenextprograminstructiontoberunfrommemory,decodeittodeterminewhatneedstobedone,andthenissuethepropercommandtotheALU,memoryandI/Ocontrollerstogetthejobdone.
2.1.2參考譯文
所有的計算機都有著相同的基本架構(gòu),無論是大型機或掌上電腦都有存儲器、I/O系統(tǒng)、算術(shù)/邏輯單元以及一個控制單元。這種架構(gòu)被命名為馮·諾依曼體系結(jié)構(gòu),由數(shù)學家約翰·馮·諾依曼構(gòu)思設計。馮·諾依曼通過廣泛描述通用計算機包含的四個基本組成部分著手開始他的“初步探索”。這些基本組成部分和算術(shù)、存儲器、控制有關(guān),同時也與人工操作密切相連。換言之,算數(shù)/邏輯單元(ALU)、存儲器、控制單元(CU)和輸入輸出(I/O)設備,這些就是電腦的經(jīng)典模型。計算機系統(tǒng)馮·諾依曼結(jié)構(gòu)如圖2.1所示。
存儲器
電腦的存儲器是為電腦執(zhí)行的所有程序指令和數(shù)據(jù)提供臨時儲存的子系統(tǒng)。它通常被稱為RAM(RandomAccessMemory,隨機存取存儲器)。存儲器被劃分為很多區(qū)間,每個區(qū)間有一個唯一的地址,可以讀取數(shù)據(jù)。
數(shù)學/邏輯單元(ALU)
該子系統(tǒng)正確執(zhí)行所有的算術(shù)運算和比較。在馮·諾依曼體系結(jié)構(gòu)中,算術(shù)/邏輯單元(ALU)和控制單元(CU)是單獨的組件,但在現(xiàn)代系統(tǒng)中,它們被集成在處理器中。ALU由3個部分組成:寄存器、ALU電路,以及它們之間的通路。該寄存器基本上是一個像RAM的存儲單元,并存儲計算結(jié)果。其運算速度較RAM快得多而且地址不同。ALU電路實際就是執(zhí)行計算,它和任何芯片一樣是由與門、非門、或門設計而成的。
控制單元(CU)
控制單元負責從內(nèi)存中獲取下一個程序的指令,對其進行解碼,以確定需要做什么工作,然后發(fā)出正確的命令ALU,由存儲器和I/O控制器完成這項工作。這些步驟是連續(xù)進行的,直到程序的最后一行由QUIT或STOP完成。
輸入-輸出(I/O)裝置
這是一個允許計算機與其他設備交互、與外界通信的子系統(tǒng)。它也負責存儲程序,如硬盤驅(qū)動器控制。
2.2ReadingMaterials
AbbreviatedasOS,anoperatingsystemisapowerful,andusuallylarge,programthatcontrolsandmanagesthehardwareandothersoftwareonacomputer.
ThemostpopularoperatingsystemstodayincludeversionsofMicrosoftWindows(likeWindows10,Windows8,Windows7,WindowsVista,andWindowsXP),Apple’sMacOS,andflavorsoftheopensourceoperatingsystemLinux.
Windows10(Fig2.2)isthenameforthenextMicrosoftWindowsoperatingsystem.TheinternalMicrosoftcodenameforWindows10isThresholdandthepresumednamewasWindows9butMicrosoftdecidedtoskipthatnumberaltogether.Windows10willintroduceanupdatedStartMenu,anotificationcenter,andsupportforvirtualdesktops.It’salsorumoredthatMicrosoftwillremovetheCharmsBarinWindows10,firstintroducedinWindows8.CortanamayalsobeavailableasanappinWindows10,evenfortraditionalcomputers.Whilethisisnotconfirmed,I'vealsoheardthatWindows10maybeafreeupgradeforWindows8owners.
Fig2.2InterfaceofWindows10
WhilenoofficialreleasedatehasbeenannouncedbyMicrosoft,Windows10isrumoredtobereleasedonorclosetoApril,2015.Windows10,oncereleased,willbethesuccessortoWindows8,Microsoft’smostcurrentversionofWindows.It’sverylikelythatWindows10willbereleasedinthreephases,similartohowWindows8wasreleased.FirstisWindows10EnterpriseTechnicalPreview,whichisabetareleaseforsoftwareandhardwaremakers,aswellastesters.
ThisversionofWindows10wasmadeavailableonOctober1,2014.SecondwilllikelybeaWindows10ConsumerPreview,ormaybeWindows10RC(ReleaseCandidate),whichisanalmost-ready,limited-time-useversionthatMicrosoftwillreleaseforfreetoawideraudience,inreturnforfeedback.Thisshouldbereleasedinearly2015.ThethirdandfinalreleasewillbethefinalcopyofWindows10,whichwillbereferredtoatMicrosoftandtocomputermakersasWindows10RTM(ReleasetoManufacturing).ThisistheversionofWindows10youwillbeabletopurchaseinApril,2015.
Windows10maybethelastmajorversionofWindowsever,withsmaller,moreincremental,improvementsmadeviaupdatesintothefuture.
2.2.2ComputerLanguages
MostCommonComputerLanguages
Thepopularityanduseofcomputerprogramminglanguagesvariesovertime,butthereareafewthathaveremainedwidelyusedforanumberofyears.Programminglanguagesareusedwithinmanydifferentcontexts,includingwebanddesktopapplications.Manyprogrammersareproficientinmorethanonelanguage,andtheavailablelanguagesaresuitedtodifferenttypesoftask.Likenaturallanguages,programminglanguagesvaryintermsofsyntaxaswellasvocabulary.
Java
Javahasremainedthemostwidelyusedlanguageforsometime.Javacanbeusedtodevelopapplicationsfortheweb,desktopandlaptopPCs,andformobiledevicesrunningmanydifferentplatformssuchasAndroid.JavaisdevelopedbySunMicrosystems,nowpartofOracle,andfeaturessimilarstructurestoolderlanguagessuchasC.Javaapplicationsaretypicallycreatedusingobject-orienteddevelopment,throughwhichapplicationresponsibilitiesaredividedupbetweenwell-definedobjects.
C
TheClanguagewasoriginallydevisedinthelate1960sandisusedtodevelopoperatingsystemsaswellasapplications.Inadditiontobeingoneofthemostusedcomputerlanguageshistorically,ChasinfluencedmanyotherpopularlanguagesincludingJava,C++andC#,anditssyntaxfeaturescanbeseenthroughoutprogrammingresources.Cisanimperativelanguage,carryingoutrequiredfunctionalitythroughaseriesofimperativeinstructions.
C++
C++wasinitiallydesignedinthelate1970sasanalternativetoC,withadditionalfeatures.C++hascharacteristicsofbothhigh-andlow-levelprogramminglanguages.High-levelprogramminginvolvesagreaterdegreeofabstraction,whereaslow-levelprogrammingcontainsmoredirectreferencestotheimplementationofaprogramwithinasystem.C++hascontinuedtobeusedbymanyprogrammers,tocreatebothsystemsandapplications.
C#
C#wasreleasedin2000,andwasinitiallyintendedtoprovideobject-orienteddevelopmentwithinMicrosoft’s.NETframework.C#canbeusedforotherprogrammingmethods,includingimperativeandfunctionaltechniques.C#isprimarilyusedinwebcontexts,todevelopInternetapplicationsandcomponents,butcanalsobeusedforsoftwareapplications.ProgrammerswhoarefamiliarwithCandC++typicallyfindC#easiertolearn,duetothesimilaritiesinsyntax.
PHP
PHP(officiallyPHP:HypertextPreprocessor)isoneofthemostwidelyusedserver-sidescriptinglanguagesontheweb.PHPcanbeusedtobuildpowerfulwebapplicationsinconjunctionwithHTMLandotherservertechnologiessuchasdatabases.PHPisusedtobuildwebsites,buildingHTMLstructureswhentheuserrequestsapageataparticularwebaddressandsendingthepagecontenttotheuser’sbrowser,whereitcanberenderedandinteractedwith.
2.2.3Viruses
TypesofComputerViruses
Youarealreadyawareofwhatcomputersareandwhatfunctionstheyperform.Beingapartofthismodernera,youmustcomeacrosswiththeterm“ComputerVirus”manytimes,whichisthebasiccauseofcomputerinfection.Itcorruptsthecomputerfilesandaffectsitsfunctioning.AviruscanspreadfromonecomputertoanotherbymeansofnetworkorbyanyremovablemediumlikeCDs,DVDs,FloppyandUSBDrives,whichmaycarryvirus.Thespreadingofthemaliciouscodeofthesevirusesisgenerallyfacilitatedbytheinternet.
Avirusisacomputerprogramthatcaneasilyreplicateitselfandcausecomputerinfection.Thissoftwareiswrittendeliberatelytomakeitsentryinacomputerwithoutanynotificationorpermissionoftheuser.Thesenastyprogramsinstallthemselves.Therearevarioustypesofviruses,whichdependsonthemaliciouseffecttheycause.Notallareequallymaliciousbuttheusershouldcheckthatitisremovedassoonaspossible,nomatteritismoreorlessharmful.Themostcommontypesofviruseslistedandexplainedbelow.Justhavealook.
ResidentViruses
Itisoneofthemostcommontypesofvirus,whichresidesinthecomputermemoryalsoknownasRAM.Thefunction,whichitperforms,istoinfectthealreadyinstalledprogramsandtheprograms,whichmayinstalledinfuture.Thisallhappensbyincorporatingamaliciouscodeinthememoryofthecomputer.Theyachievethisbyallocatingaspacefortheminthememoryofthecomputer.Thevirusescanaffecttheotherfilesonlybyestablishingaprocess,whichcanactivatethemaliciouscodetofunction.
Therearevarioustypesofprocesses,whichdevelopedbythevirusestostartitsfunctioning.ThemostcommonofthemisTSR(Terminate-Stay-Resident)interruptfunctionandmanipulationofMCBs(MemoryControlBlocks).TheTSRinterruptfunctioningmethodissimplestforthevirustoarouseinfectionbutthescannerscanalsodetectitveryeasily.Thisinterruptsalltheexecutionsbycorruptingprogramsandfilesthatclosed,openedorrenamed.
Thedetectionisveryeasyasitachievedbyreferringtothelocalharddrive’smap.Theresidentvirusdetectedbyantiviruswithin-depthscanningefficiencyonly.TheexamplesofthistypeofvirusesareMeve,Mrklunky,RandexandCMJ.
OverwriteViruses
ThistypeofvirusesinfectsthewiderangeofoperatingsystemssuchasMacintosh,Linux,Dosandwindows.Thevirusgenerallyattacksafile,whichbecomesitsvictimandafterthis,thevirusoverwritethefilewiththemaliciouscode.Iftheinfectionnotdetectedontime,theinfectedfilecancausedamagetotheotherfilesirreversibly.Thecomputersysteminfectedwithsuchtypeofvirusbecomesinoperableanddonotperformfunctionsnormally.Theinfectedfilescannotdisinfectbuttheonlythingcanhappenistheremovalofthecorruptedfileandrestoringitfromthebackupresource.TheexamplesofthistypeofvirusesareTrivial.88.D,Way,Trj.Reboot.
DirectActionViruses
Whenthisvirusisexecutedinthecomputeritstartsreplicatingandtakingactiononthefilesanddirectories.TheseinfectthefilesinadirectoryandalsothedirectorieshavingthosefilesthatarespecifiedintheAUTOEXEC.BATfilepath.Generally,batchfilesofthistypearelocatedintherootdirectoryoftheharddriveanditalsoperformssomefunctionswhenthecomputerisbooted.
Bootviruses
Thesearetheviruseswhichaffectthebootsectorofthediskettesandtheharddrives.Everyharddriveordiskettehassectorsandthefirstsectorisknownasthebootsector.IthasMBR(MaterBootRecord)whichfunctionstoreadandloadtheOS(OperatingSystem).Ifyoure-bootthecomputerwhilethediskhavingvirusinfectedbootisinthedrivethenitcancauseinfectiontotheharddriveofthesystem.Assoonastheharddrivegetsinfected,allthedisketteswillautomaticallygetinfected.Youcancheckthisvirusbyusingantivirussoftware.
PolymorphicViruses
Thisisoneofthosetypesofviruseswhichareverycomplexthreatstocomputers.Everytometheyinfectthecomputersystem,theyproducecopiesofthemselvesbyencryptingorencodingthemisadifferentway.Allthecopiesarefunctionallyactivebutslightlymodifiedofthepreviousone.Toencryptinadifferentway,theyusedifferentencryption
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