Tải bản đầy đủ - 0 (trang)
Chapter 15.  Software and Operating Systems

Chapter 15.  Software and Operating Systems

Tải bản đầy đủ - 0trang

TheBootProcess

Thetermbootcomesfromthewordbootstrapanddescribes

themethodbywhichthelaptopbecomesoperational.Justas

youpullonalargebootbythesmallstrapattachedtotheback,

alaptoploadsalargeoperatingsystembyfirstloadingasmall

programthatcanthenpulltheoperatingsystemintomemory.

Thechainofeventsbeginswiththeapplicationofpowerand

finallyresultsinafullyfunctionalcomputersystemwith

softwareloadedandrunning.Eacheventistriggeredbythe

eventbeforeitandinitiatestheeventafterit.

Howdoesunderstandingthebootprocesshelpyousolve

problems?Well,forone,ifyoucan'tstartyoursystem,tracing

thesystembootprocessmighthelpyoufindthelocationofa

problemifyouexaminetheerrormessagesthesystemdisplays

whentheproblemoccurs.Additionally,Windowscangeneratea

bootlogthatyoucanthenusetotraceexactlywhenafailure

occurred.Ifyouseeanerrormessagethatisdisplayedbyonly

aparticularprogram,youcanbesuretheprograminquestion

wasatleastloadedandpartiallyrunning.Combinethis

informationwiththeknowledgeofthebootsequence,andyou

canatleasttellhowfarthesystem'sstartupprocedurehad

progressedbeforetheproblemoccurred.Youusuallyshould

lookatwhicheverfilesordiskareaswerebeingaccessedduring

thefailureinthebootprocess.Errormessagesdisplayedduring

thebootprocessandthosedisplayedduringnormalsystem

operationcanbehardtodecipher.However,thefirststepin

decodinganerrormessageisknowingwherethemessage

camefromwhichprogramactuallygeneratedordisplayedit.

Thefollowingprogramsanddevicesarecapableofdisplaying

errormessagesduringthebootprocess.

Operatingsystemindependent:



MotherboardROMBIOS

AdaptercardROMBIOSextensions

Master(partition)bootrecord

Volumebootrecord(VBR)

Operatingsystemdependent.DOSandWindows9x/Meusethe

followingfilesduringsystemstartup:

Systemfiles(IO.SYS/IBMBIO.COMandMSDOS.SYS/IBMDOS.COM)

Devicedrivers(loadedthroughCONFIG.SYSortheWindows

RegistrySYSTEM.DAT)

Shellprogram(COMMAND.COMinDOS)

ProgramsrunbyAUTOEXEC.BAT,theWindowsStartupgroup,

andtheRegistry

Windows(WIN.COM)

WindowsNT/2000/XPusethefollowingfilesduringsystem

startup:

Ntldr



Boot.ini

Bootsect.dos(multiple-bootsystemsonly)

Ntbootdd.sys(loadedonlyforSCSIdrives)



NTDetect.com



Ntoskrnl.exe



Hal.dll



Filesinsystemroot\System32\Config(Registry)

Filesinsystemroot\System32\Drivers(drivers)

Thefirstportionofthestartupsequenceisoperatingsystem

independent,whichmeansthesestepsarethesameforall

laptops,nomatterwhichoperatingsystemisinstalled.The

latterportionofthebootsequenceisoperatingsystem

dependent,whichmeansthesestepscanvarydependingon

whichoperatingsystemisinstalledorbeingloaded.The

followingsectionexaminestheoperatingsystemindependent

startupsequenceandprovidesadetailedaccountofmanyof

theerrormessagesthatmightoccurduringthisprocess.Ialso

providesolutionstotheseerrormessagessoyoucangetyour

systemworkingasquicklyaspossible.



TheBootProcess:OperatingSystem

Independent

Ifyouhaveaproblemwithyoursystemduringstartupandcan

determinewhereinthissequenceofeventsyoursystemhas

stalled,youknowwhicheventshaveoccurredandprobablycan

eliminateeachofthemasacauseoftheproblem.Thefollowing

stepsoccurinatypicalsystemstartupregardlessofwhich

operatingsystemyouareloading:

1. Youswitchonelectricalpowertothesystem.



2. ThepowersupplyperformsaPowerOnSelfTest(knownas

thePOST).Whenallvoltagesandcurrentlevelsare

acceptable,thesupplyindicatesthatthepowerisstableand

sendsthePower_Goodsignaltothemotherboard.Thetime

fromswitch-ontoPower_Goodisnormallybetween0.1and

0.5seconds.

3. ThemicroprocessortimerchipreceivesthePower_Good

signal,whichcausesittostopgeneratingaresetsignaltothe

microprocessor.

4. ThemicroprocessorbeginsexecutingtheROMBIOScode,

startingatmemoryaddressFFFF:0000.Becausethislocation

isonly16bytesfromtheendoftheavailableROMspace,it

containsaJMP(jump)instructiontotheactualROMBIOS

startingaddress.

5. TheROMBIOSperformsatestofthecentralhardwareto

verifybasicsystemfunctionality.Anyerrorsthatoccurare

indicatedbyaudio"beep"codesbecausethevideosystemhas

notyetbeeninitialized.IftheBIOSisPlugandPlay(PnP),the

followingsteps(steps69)areexecuted;ifnot,skiptostep

10.

6. ThePlugandPlayBIOSchecksnonvolatilerandomaccess

memory(RAM)forinput/output(I/O)portaddresses,

interruptrequest(IRQ)lines,directmemoryaccess(DMA)

channels,andothersettingsnecessarytoconfigurePnP

devicesonthecomputer.

7. AllPlugandPlaydevicesfoundbythePlugandPlayBIOSare

disabled.

8. Amapofusedandunusedresourcesiscreated.

9. ThePlugandPlaydevicesareconfiguredandreenabled,one



atatime.IfyourcomputerdoesnothaveaPlugandPlay

BIOS,PnPdevicesareinitializedusingtheirdefaultsettings.

ThesedevicescanbereconfigureddynamicallywhenWindows

starts.Atthatpoint,WindowsqueriesthePlugandPlayBIOS

fordeviceinformationandthenquerieseachPlugandPlay

deviceforitsconfiguration.

10. TheBIOSperformsavideoROMscanofmemorylocations

C000:0000C780:0000lookingforvideoadapterROMBIOS

programscontainedonavideoadapterfoundeitheronacard

pluggedintoaslotorintegratedintothemotherboard.Ifthe

scanlocatesavideoROMBIOS,itistestedbyachecksum

procedure.IfthevideoBIOSpassesthechecksumtest,the

ROMisexecuted;thenthevideoROMcodeinitializesthe

videoadapterandacursorappearsonscreen.Ifthechecksum

testfails,thefollowingmessageappears:

C000ROMError

Becauselaptopcomputersdon'tuseremovablevideocards

(thevideocircuitiseitherintegratedintothemotherboard's

chipsetoraseparatechipisbuiltintothemotherboard),this

errormeansyouneedtohaveyoursystemserviced.

11. IftheBIOSfindsnovideoadapterROM,itusesthe

motherboardROMvideodriverstoinitializethevideodisplay

hardware,andacursorappearsonscreen.

12. ThemotherboardROMBIOSscansmemorylocations

C800:0000DF80:0000in2KBincrementsforanyotherROMs

locatedonanyotheradaptercards(suchasSCSIadapters).If

anyROMsarefound,theyarechecksum-testedandexecuted.

TheseadapterROMscanalterexistingBIOSroutinesand

establishnewones.



13. FailureofachecksumtestforanyoftheseROMmodules

causesthismessagetoappear:

XXXXROMError

Here,theaddressXXXXindicatesthesegmentaddressofthe

failedROMmodule.

IfyouhaveaPCCardorCardBuscardinstalled,shutdown

thesystem,removethecard,andthenrestartthesystem.If

theerrorisnolongerdisplayed,theROMbuiltintothecardis

defective,andthecardshouldbereplaced.Iftheerror

messagestillappears,yoursystemshouldbeserviced,

becausetheerrorisprobablycomingfromROMonthe

motherboard.

14. TheROMBIOSchecksthewordvalueatmemorylocation

0000:0472toseewhetherthisstartisacoldstartorawarm

start.Awordvalueof1234hinthislocationisaflagthat

indicatesawarmstart,whichcausestheBIOStoskipthe

memorytestportionofthePOST.Anyotherwordvalueinthis

locationindicatesacoldstart,andtheBIOSperformsthefull

POSTprocedure.SomesystemBIOSesletyoucontrolvarious

aspectsofthePOSTprocedure,makingitpossibletoskipthe

memorytest,forexample,whichcanbelengthyonasystem

withalotofRAM.

15. Ifthisisacoldstart,thefullPOSTexecutes;ifthisisawarm

start,amini-POSTexecutes,minustheRAMtest.Anyerrors

foundduringthePOSTarereportedbyacombinationofaudio

anddisplayederrormessages.Successfulcompletionofthe

POSTisusuallyindicatedbyasinglebeep(withtheexception

ofsomeCompaqcomputers,whichbeeptwice).SeeChapter

16,"ProblemSolvingandTroubleshooting,"forinformation

abouterrormessages,beepcodes,andsolutions.



16. TheROMBIOSsearchesforabootrecordatcylinder0,head

0,sector1(thefirstsector)onthedefaultbootdrive.Atone

time,thedefaultbootdrivewasalwaysthefirstfloppydisk

(A:)drive.However,theBIOSesontoday'ssystemsoften

enableyoutoselectthedefaultbootdeviceandtheorderin

whichtheBIOSwilllookforotherdevicestobootfrom,if

necessary,usingafloppydisk,harddisk,orevenaCD-ROM

driveinanyorderyouchoose.Thissectorisloadedinto

memoryat0000:7C00andtested.

Ifadiskisinthedrivebutthesectorcan'tberead,orifno

diskispresent,theBIOScontinueswithstep19.



Tip

IfyoudowanttobootfromaCD-ROM,besurethe

CD-ROMdriveisspecifiedbeforetheharddiskinthe

bootdevicesmenuinyourBIOSsetup.Toensurethat

youcanbootfromanemergencyCDorfloppydisk,I

recommendsettingtheCD-ROMdriveasthefirstboot

deviceandthefloppydriveasthesecondbootdevice.

Aharddiskcontainingyouroperatingsystemshould

bethethirddeviceinthebootdevicelist.Thisenables

youtoalwaysbereadyforanemergency.Aslongas

youdonotbootwithaCDorfloppyloaded,theBIOS

bypassesboththeCD-ROMandfloppydiskdrivesand

bootsfromtheharddrive.

NotethatnotalloperatingsystemCDsarebootable.

Windows95CDsarenotbootable;however,with

Windows98,MicrosoftmadetheoperatingsystemCD

bootable,butonlyfororiginalequipmentmanufacturer

(OEM)versions.Thisdoesnotextendtoretailversions

oftheseWindowsCDs.WindowsNT4.0andlater,

includingWindows2000andXP,areshippedon



bootableCDs.SeeChapter10,"RemovableStorage,"

forinformationonhowtomakeabootableCD.

MostrecoveryCDspackagedwithlaptopcomputers

canalsobeusedtobootthesystemandstartthe

software/operatingsystemreinstallationprocess.

17. Ifyouarebootingfromafloppydiskandthefirstbyteofthe

volumebootrecordislessthan06h,orifthefirstbyteis

greaterthanorequalto06handthefirstninewordscontain

thesamedatapattern,thiserrormessageappearsandthe

systemstops:

602-DisketteBootRecordError

Ifyou'veleftthefloppydiskinthedrivebymistake,removeit

andrestartthesystem.Ifthefloppydiskissupposedtobe

bootable,reformatitwiththe/S(system)orBootFilesoption

andrestartyoursystemwithit(usetheFilemenuinWindows

ExplorerofaworkingsystemtoaccesstheFormatoption).

18. Ifthevolumebootrecordcan'tfindorloadthesystemfiles,or

ifaproblemwasencounteredloadingthem,oneofthe

followingmessagesappears:

Non-Systemdiskordiskerror

Replaceandstrikeanykeywhenready

Non-Systemdiskordiskerror

Replaceandpressanykeywhenready

Invalidsystemdisk_

Replacethedisk,andthenpressanykey

DiskBootfailure

DiskI/OError



Allthesemessagesoriginateinthevolumebootrecordand

relatetoVBRorsystemfileproblems.Theexacterror

messageyouseedependsupontheBIOSversionusedby

yourlaptop.

Themostcommoncausefortheseerrormessagesisleavinga

floppydiskindriveA:.Removethefloppydiskandpressa

keytoretrythebootprocess.

19. IfnobootrecordcanbereadfromdriveA:(suchaswhenno

diskisinthedrive),theBIOSthenlooksforamasterboot

record(MBR)atcylinder0,head0,sector1(thefirstsector)

ofthefirstharddisk.Ifthissectorisfound,itisloadedinto

memoryaddress0000:7C00andtestedforasignature.

20. Ifthelasttwo(signature)bytesoftheMBRarenotequalto

55AAh,softwareinterrupt18h(Int18h)isinvokedonmost

systems.

ThiscausestheBIOStodisplayanerrormessagethatcan

varyfordifferentBIOSmanufacturers,butit'softensimilarto

oneofthefollowingmessages,dependingonwhichBIOSyou

have.

IBMBIOS:

TheIBMPersonalComputerBasic_

VersionC1.10CopyrightIBMCorp1981

62940Bytesfree_

Ok_

MostIBMcomputerssince1987displayastrangecharacter

graphicdepictingthefrontofafloppydrive,a31/2"disk,and

arrowspromptingyoutoinsertadiskinthedriveandpress



theF1keytoproceed.

AMIBIOS:

NOROMBASIC-SYSTEMHALTED

CompaqBIOS:

Non-Systemdiskordiskerror

replaceandstrikeanykeywhenready

AwardBIOS:

DISKBOOTFAILURE,INSERTSYSTEMDISKANDPRESSENTER

PhoenixBIOS:

NobootdeviceavailablestrikeF1toretryboot,F2forsetuputility

or

NobootsectoronfixeddiskstrikeF1toretryboot,F2forsetuputility

Notethatalthoughsomeofthesemessagesaresimilarto

thosecausedbyleavingafloppydiskindriveA:(step18),

somearedifferent.AlthoughthemessagesvaryfromBIOSto

BIOS,thecauseforeachrelatestospecificbytesintheMBR,



whichisthefirstsectorofaharddiskatthephysicallocation

cylinder0,head0,sector1.

Theprobleminvolvesadiskthateitherhasneverbeen

partitionedorhashadthemasterbootsectorcorrupted.

Duringthebootprocess,theBIOSchecksthelasttwobytesin

theMBR(thefirstsectorofthedrive)forasignaturevalueof

55AAh.Ifthelasttwobytesarenot55AAh,aninterrupt18his

invoked,whichcallsthesubroutinethatdisplaysoneofthe

errormessagesjustshown,whichbasicallyinstructstheuser

toinsertabootablefloppytoproceed.

TheMBR(includingthesignaturebytes)iswrittentothehard

diskbytheFDISKorDISKPARTprogram(whichareusedby

variousversionsofDOSorWindowstopartitionthehard

disk).Immediatelyafteraharddiskislow-levelformatted,all

thesectorsareinitializedwithapatternofbytes,andthefirst

sectordoesnotcontainthe55AAhsignature.Inotherwords,

theseROMerrormessagesareexactlywhatyouseeifyou

attempttobootfromaharddiskthathasbeenfreshlylowlevelformattedbuthasnotyetbeenpartitioned.

Youshouldseeanerrormessagelikethisonlyifyouhave

replacedtheoriginalharddiskinyourlaptopwithanother

harddiskthathasnotyetbeenpartitioned,oriftheMBRon

thecurrentdiskhasbeencorrupted.

21. TheMBRsearchesitsbuilt-inpartitiontableentriesforaboot

indicatorbytemarkinganactivepartitionentry.

22. Ifnoneofthepartitionsaremarkedactive(bootable),the

BIOSinvokessoftwareinterrupt18h,whichdisplaysanerror

message(refertostep20).

Thiserrorcouldhappenifyoupartitionaharddiskintoa

primaryandextendedpartitionwithFDISKandforgettomark

theprimarypartitionasactive.



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Chapter 15.  Software and Operating Systems

Tải bản đầy đủ ngay(0 tr)

×
x