bandwidth

Meaningincomputersystems

Thetermbandwidthoriginallyreferstothewidthoftheelectromagneticwavefrequencyband,thatis,thedifferencebetweenthehighestfrequencyandthelowestfrequencyofasignal.Atpresent,itismorewidelyusedindigitalcommunicationtodescribethetheoreticalmaximumrateofdatatransmissiononanetworkorline.Thisisnotitsacademicdefinition,butithasbeenextendedtouse.

• Busbandwidthreferstothetotalamountofdatathatthebuscantransmitinaunittime,whichisequaltotheproductofthebusbitwidthandtheoperatingfrequency.Forexample:fora64-bit,800MHzfront-sidebus,itsdatatransferrateisequalto64bit×800×1000×1000Hz÷8(Byte)÷1024÷1024÷1024≈6.0GB/s

• Memorybandwidthreferstothedatatransmissioncapacitythatthememorybuscanprovide.Forexample:thedatatransmissionfrequencyofDDR400memoryis200MHz,thenasinglemodulehas64bit×200×2(ddristheupperandloweredgeacquisitionsignal)×1000×1000Hz÷8(Byte)÷1024÷1024÷1024≈3.0GB/sBandwidth.

Application

I.Bandwidth

ThebandwidthofthesignalreferstotheThefrequencyrangeoccupiedbythevariousfrequencycomponentscontained.Bandwidthisespeciallyimportantforbasicinput/outputsystem(BIOS)devices,suchasfastdiskdrives,whicharehinderedbylow-bandwidthbuses.

Second,theabilityofthecommunicationlinetotransmitdata

Whatcanbepassedfromonepointtoanotherpointinthenetworkinaunitoftime"Highestdatarate".Fortheconceptofbandwidth,amorevividanalogyisthehighway.Theamountofdatathatcanbetransmittedonthewireperunittime,thecommonlyusedunitisbps(bitpersecond).Thebandwidthofacomputernetworkreferstothehighestdataratethatthenetworkcanpassthrough,thatis,howmanybitspersecond.

Strictlyspeaking,thebandwidthofadigitalnetworkshouldbeexpressedinbaudrate,whichmeansthenumberofpulsespersecond.Bitistheunitofinformation.Sincedigitalequipmentusesbinarysystem,theamountofinformationcarriedbyeachbitlevelisthelogarithmofbase2.Ifitisquaternary,itisthelogarithmofbase2.Theamountofinformationcarriedbyeachbitlevelis2.Therefore,intermsofvalue,thebaudisthesameasthebit.Sincepeoplearenotveryclearaboutthetwoconcepts,bitrateisoftenusedtoexpressrate.Itisalsobecausetherearetoomanypeopleusingbits,sobitratehasbecomeadefactostandardnameforbandwidth.

bit/s=1Kbit/s

bit/s=1Mbit/s

Whendescribingbandwidth,"bit/sec"isoftenomitted.Forexample,ifthebandwidthis1M,itisactually1Mbps,whereMbpsreferstomegabits/s.

Therearetwodifferentspeedsinthenetwork:

1.Thepropagationspeedofthesignal(ieelectromagneticwave)onthetransmissionmedium(m/s,orkm/s).

2.Therateatwhichthecomputersendsbitstothenetwork(bitspersecond).

Themeaningsandunitsofthesetworatesarecompletelydifferent.

Beforeunderstandingtheconceptofbandwidth,wefirstlookataformula:bandwidth=clockfrequencyxnumberofbusbits/8(unitB/s),fromtheformulawecanseethatbandwidthandclockfrequencyThenumberofbusbitsisverycloselyrelated.Infact,inacomputersystem,notonlydoesthemonitorandmemoryhavetheconceptofbandwidth,butonaboardcard,theconceptofbandwidthisevenmore.Itcanbesaidthatbandwidthiseverywhere.

Sowhatexactlyisbandwidth?Whatisthemeaningofbandwidth?Inordertounderstandtherelationshipbetweenbandwidth,bitwidth,andclockfrequencymorevividly,let'stakeamorevividexample.Ifaworkerprocessesparts,ifonepersondoesit,itisdefinitelynotasgoodastwopeopledoitatthesameprocessingspeed.Bandwidthislikethetotalnumberofpartsthatworkerscanprocess.Bitwidthislikethenumberofworkers.Theclockfrequencyisequivalenttothespeedofprocessingasinglepart.Thewiderthebitwidthandthehighertheclockfrequency,thelargerthebusbandwidth.Thebenefitsareobvious.

Thereareusuallytwolargerchipsonthemotherboard.Generally,theoneneartheCPUiscalledtheNorthBridge,andtheonefarawayfromtheCPUiscalledtheSouthBridge.TheroleofthenorthbridgeistoestablishacommunicationinterfacebetweentheCPU,memory,andgraphicscard.Thebandwidthbetweenthemandthenorthbridgelargelydeterminestheperformanceofthememoryandgraphicscard.TheSouthBridgeisresponsibleforthecomputer'sI/Odevices,PCIdevicesandharddisks.ComparedwiththeNorthBridge,thebandwidthrequirementsaresmaller.Theconnectionbandwidthbetweenthenorthandsouthbridgesisgenerallycalledthenorthandsouthbridgebandwidth.Withthedevelopmentofcomputersinthedirectionofmultimedia,thefunctionsoftheSouthBridgearebecomingmorepowerful,andnewrequirementshavebeenputforwardforthebandwidthoftheconnectionbusbetweentheNorthandSouthbridges.OnINTEL's9X5seriesmotherboards,thebandwidthoftheSouthandNorthbridgeswillremainunchangedfrombefore.Thecriticized266MB/Shasgrowntoanunprecedented2GB/S,whichsolvedthebandwidthbottleneckbetweenthenorthandsouthbridgesinonefellswoop.

Bandwidthinthegraphicscard

Friendswhoplaygamesknowthatwhenplayingsomelarge-scalegames,thescreensometimesgetsstuck.Infact,thisistheproblemofinsufficientgraphicscardbandwidth.Tobemorespecific,thisisinsufficientvideomemorybandwidth.Asweallknow,theleadingAGPinterfaceisAGP8X,andthefrequencyoftheAGPbusistwicethatofthePCIbus,whichis266MHz.Itiseasytoconvertitsbandwidthto2.1Gbps.Thisbandwidthisveryinsignificant,becauseThememorybandwidthofthemostcommonATIR9000mustreach400MHz*128Bit/8=6.4GB/s,nottomentionotherhigh-endgraphicscards.Becauseofthis,INTELusesthePCI-Expressbustoreplacetheold-fashionedAGPbusinthelatest9X5chipset.ComparedwiththetraditionalPCIandthesharedparallelarchitectureofearliercomputerbuses,thebiggestfeatureofPCIExpressistheequipmentApoint-to-pointserialconnectionisusedtoalloweachdevicetohaveitsowndedicatedconnection.Thereisnoneedtorequestbandwidthfromtheentirebus.Atthesametime,theuseofserialconnectioncharacteristicswilleasilyincreasethedatatransmissionspeedtoaveryhighlevel.frequency.Intermsoftransmissionspeed,becausePCIExpresssupportsatwo-waytransmissionmode,eachconnecteddevicecanusethemaximumbandwidth.ThebandwidthbottleneckencounteredbyAGPisalsosolved.

Thebandwidthinthebus

Inacomputersystem,thebusislikethenervoussysteminthehumanbody.Itassumestheresponsibilityofalldatatransmission,andthevarioussubsystemsAllcommunicationmustbebasedonthebus.Forexample,thereisafrontsidebusbetweentheCPUandthenorthbridge,theAGPbusbetweenthenorthbridgeandthegraphicscard,andthenorthandsouthbridgebusbetweenthechipset.VariousexpansiondevicesareconnectedtothesystemthroughPCIandPCI-Xbuses;Theconnectionwiththeexternalequipmentisalsocarriedoutthroughthebus,thepopularUSB2.0,IEEE1394bus,etc.,inaword,inacomputersystem,alldataexchangeneedsmustberealizedthroughthebus!

Accordingtothedifferentworkingmodes,thebuscanbedividedintotwotypes.Oneisaparallelbus,whichcantransmitmultiplebitsofdataatthesametime.Itislikeaspaciousroadthatallowsmultiplecarstorunsidebyside.Italsohastwo-wayandone-waypoints;theotherisaserialbus,whichcanonlytransmitonepieceofdataatthesametime,whichislikeanarrowroadthatonlyallowsonecartowalkon.Thedatamustbetransmittedonebyone,whichlookslikealongThelongdatastringiscalled"serial".

Forserialbuses,theconceptofbandwidthandoperatingfrequencyisexactlythesameasthatofparallelbuses,butitchangestheconceptofbusbitwidthinthetraditionalsense.Inthecaseofthesamefrequency,theparallelbusismuchfasterthantheserialbus,butithasinterferencebetweenparalleltransmissionsignals.Thehigherthefrequencyandthelargerthebitwidth,themoreserioustheinterference.Therefore,theexistingparallelbusmustbegreatlyimprovedThebandwidthoftheserialbusisverydifficult;whiletheserialbusdoesnothavethisproblem,thebusfrequencycanbegreatlyincreased,sothattheserialbuscanobtainhighbandwidthbyvirtueofthehighfrequency.Inordertomakeupfortheshortcomingofonlyonebitofdatacanbetransmittedatatime,serialbusesoftenusemultiplepipelines(orchannels)toachievehigherspeeds-thepipelinesareindependent,andmultiplepipelinesformabussystem.Itseemsthatitisverysimilartoaparallelbus,butinternallyitoperatesonaserialprinciple.Forthistypeofbus,thecalculationformulaforbandwidthisequalto"busfrequency×numberofpipelines".ExamplesofthisarePCIExpressandHyperTransport.Theformerhasmultipleversionsof×1,×2,×4,×8,×16,and×32.InthefirstgenerationofPCIExpresstechnology,thesingle-channelunidirectionalsignalfrequencycanreach2.5GHz.Let’stake×16asanexample,where16represents16pairsofbidirectionalbuses,atotalof64lines,andeach4linesformachannel.Twotoreceiveandtwotosend.Inthisway,wecancalculatethebandwidthofthebusas2.5GHz×16/10=4GB/s(one-way).Divideby10becauseeachbyteuses10-bitencoding.

Thereisacertaindifferencebetweenthedescriptionparametersoftheparallelbusandtheserialbus.Foraparallelbus,theperformanceparametersdescribedhavethefollowingthree:buswidth,clockfrequency,anddatatransmissionfrequency.Amongthem,thebuswidthisthenumberofbitsthatthebuscantransmitdataatthesametime,whichislikethenumberofvehiclesthatthelaneallowstowalksidebyside;forexample,thedatatransmittedbya16-bitbusatthesametimeis16bits,thatis,2bytes;andA32-bitbuscantransmit4bytesatthesametime,anda64-bitbuscantransmit8bytesatthesametime...Obviously,thewiderthebus,themoredataitcantransmitatthesametime.However,thebitwidthofthebuscannotbeincreasedindefinitely.

Thebandwidthofthebusreferstothetotalamountofdatathatthisbuscantransmitinaunittime,whichisequaltotheproductofthebusbitwidthandtheoperatingfrequency.Forexample,fora64-bit,800MHzfront-sidebus,itsdatatransferrateisequalto64bit×800MHz÷8(Byte)=6.4GB/s;thedatatransferrateofa32-bit,33MHzPCIbusis32bit×33MHz÷8=133MB/s,wait,thisrulecanbeappliedtoallparallelbuses-seeinghere,readersshouldunderstandthatthebusbandwidthwearetalkingaboutreferstoitsdatatransmissionrate,infact,theconceptof"busbandwidth"isthesameas"circuitbandwidth"Theoriginalconceptof"hasbeenirrelevant."

Bandwidthinmemory

Inadditiontobuses,memoryalsohasasimilarconceptofbandwidth.Infact,theso-calledmemorybandwidthreferstothedatatransmissioncapacitythatthememorybuscanprovide,butitisdeterminedbythememorychipandmemorymoduleratherthanthepurebusdesign,andthestatusisimportant,anditisoftendiscussedasaseparateobject.

ThebusbitwidthofSDRAM,DDRandDDRⅡis64bits,andthebitwidthofRDRAMis16bits.Thetwoareverydifferentinstructure:the64-bitbusofSDRAM,DDRandDDRⅡmustberealizedbymultiplechips.Thecalculationmethodisasfollows:memorymodulebitwidth=memorychipbitwidth×numberofsingle-sidedchips(assumingItisasingle-sidedsinglephysicalbank);ifthebitwidthofthememorychipis8bits,thentheremustbeonly8chipsinthemodule,andonemoreoronelessisnotallowed;ifthebitwidthofthechipFor4bits,themodulemusthave16chips.Obviously,inordertoachievehighermodulecapacity,itisagoodwaytouselow-bitwidthchips.ThisisnotthecaseforRDRAM.Itsmemorybusisaserialarchitecture,andthebusbitwidthisequaltothebitwidthofthememorychip.

Liketheparallelbus,thebandwidthofthememoryisequaltotheproductofthebitwidthandthedatatransmissionfrequency.Forexample,ifthedatatransmissionfrequencyoftheDDR400memoryis400MHz,thenasinglemodulehas64bit×400MHz÷8(Byte)=3.2GB/sbandwidth;PC800standardRDRAMfrequencyreaches800MHz,andthebandwidthofasinglemoduleis16bit×800MHz÷8=1.6GB/s.Inordertoachievehigherbandwidth,itisanidealwaytousedual-channeltechnologyinthememorycontroller.Theso-calleddual-channelistoallowtwosetsofmemorytooperateinparallel,thetotalbitwidthofthememoryisdoubled,andthebandwidthisalsodoubled.!Bandwidthcanbesaidtobethemostimportantindicatorofmemoryperformance.Theindustryalsousesmemorybandwidthasthemainclassificationstandard,butitisnottheonlyfactorthatdeterminesperformance.Inpracticalapplications,theimpactofmemorylatencyisnolessthanthatofbandwidth.Ifthedelaytimeistoolong,itisquitedisadvantageous.Atthistime,evenifthebandwidthishigh,itwillnothelp.

Theproblemofbandwidthmatching

Thereareallkindsofbusesinthecomputersystem,whichinevitablybringsabouttheproblemofbusspeedmatching.Themostcommonproblemsarethefront-sidebusandthememory,northandsouthBridgebusandPCIbus.

Whetherthefront-sidebusmatchesthememoryhasthegreatestimpactontheentiresystem.Theidealsituationisthatthefront-sidebusbandwidthisequaltothememorybandwidth,andthememorylatencyshouldbeaslowaspossible.WhenPentium4wasfirstlaunched,IntelusedRDRAMmemorytomatchthefront-sidebus,butRDRAMwasexpensive,whichseriouslyaffectedthepromotionwork.Inteloncelaunchedthe845chipsetwithPC133SDRAM,butSDRAMcanonlyprovide1.06GB/sofbandwidth.Itisonlyequivalentto1/3ofthebandwidthofthe400MHzfront-sidebus.Theseveremismatchcausedasignificantdropinsystemperformance.Later,Intelintroducedthe845DthatsupportsDDR266andbarelyimproved,butitstillhasnotachievedmatchingwiththefront-sidebus.Then,IntelchangedtheP4front-sidebusIncreasedto533MHz,bandwidthincreasedto5.4GB/s,althoughthesupportingchipsetcansupportDDR333memory,itcanonlymeet1/2;thefrontsidebusofP4isincreasedto800MHz,andthesupporting865/875PchipsetcansupportdualChannelDDR400-Atthistime,theidealstateofmatchingisrealized.Ofcourse,itisnotverymeaningfultocontinuetoincreasethememorybandwidthatthistime,becauseitexceedsthereceivingcapacityofthefrontsidebus.

Thebandwidthofthenorth-southbridgebususedtobeasharpproblem.TheearlychipsetsusedthePCIbustoconnectthenorth-southbridge,andthebandwidthitcanprovideisonly133MB/s.IfthesouthbridgeconnectstwoAnATA-100harddrive,a100Mnetwork,anIEEE1394interface...themere133MB/sbandwidthisboundtoformaseriousbottleneck.Forthisreason,variouschipsetmanufacturershavedevelopeddifferentnorth-southbridgebussolutions,suchasIntel’sHub-Link,VIA'sV-Link,SiS'sMuTIOL,AMD'sHyperTransport,andsoon,theirbandwidthhasgreatlyexceeded133MB/s,thehighestrecordhasexceeded1GB/s,thebottleneckeffectnolongerexists.

InsufficientPCIbusbandwidthisstillabigcontradiction.ThePCIbusesusedonPCsareall32-bit,33MHztype,withabandwidthof133MB/s,andthisareaof​​133MB/smustmeetthenetworkandharddiskcontrolcard(Ifthereisany)expansionneeds,oncethegigabitnetworkisused,thebottleneckwillappearimmediately.TheindustryintendstoreplacethePCIbuswiththePCIExpressbusin2004.Bythen,theproblemofinsufficientPCIbandwidthwillbecomeahistory.

Thesignificanceofbandwidthinadigitalsignalsystem

Inadigitalsignalsystem,bandwidthisusedtoidentifytheabilityofacommunicationlinetotransmitdata,thatis,topassthroughacertainpointinthenetworkwithinaunitoftimeThehighestdatarate,thecommonlyusedunitisbps(alsoknownasbitrate---bitpersecond,howmanybitspersecond).Whendescribingbandwidthindailylife,bpsisoftenomitted.Forexample,ifthebandwidthis4M,thefullnameshouldbe4Mbps.

Inviewofthereductionofbandwidthcost,theuseraccessrateisgettinghigherandhigher,fromtheinitialdial-upto20Moreven100Mopticalfiber.

Butwiththedevelopmentofcomputers,users’awarenessof‘bandwidth’shouldalsobemoreimproved.

Generallyspeaking,bandwidthisexpressedinbits,andoperatorssuchasChinaTelecom,ChinaUnicom,andChinaMobileoftenignorethisunitwhenpromoting.

Thenormalconversionconditionsareasfollows:

1Mbit=128KB

2Mbit=256KB

(andsoon)

TheconvertedspeedisyourrealInternetspeed

Inotherwords,ifthebandwidthyousubscribefromyourcarrieris10M,thensubstitutethecalculationformulaandusethe1Mconvertedabovetomeasure

Then:

(1M=1024K)

1M/128K=1024/128=8

10/8=1.25M

Inotherwords,ifyouturnon10Mbandwidth,youcanreachaspeedofupto1.25M.

Generallyspeaking,4Mbandwidthissufficientforwatchingmovies,playinggames,etc.onacomputer.Butifyouneedtodownloadlargefilesfrequently,itisrecommendedtouseahigherbandwidth

Significanceinananalogsignalsystem

Inananalogsignalsystem,bandwidthisusedtoidentifythetransmissionsignaloccupancyThewidthofthefrequencyisdeterminedbythehighestfrequencyandthelowestfrequencyofthetransmittedsignal.Thedifferencebetweenthetwoisthebandwidthvalue,soitisalsocalledthesignalbandwidthorcarrierfrequencybandwidth,andtheunitisHz.

Bandwidthisactuallyameasureofthefrequencyspectrumoccupiedbyasignal,whichcanberegardedasaspace-relatedquantity.Incontrast,thetransmissionrateofasignalisaphysicalquantityrelatedtobothspaceandtime,definedastheamountofdatatransmittedonthechannelperunittime.

Inordertousespectrumresourcesrationally,theInternationalTelecommunicationUnion(ITU)hasstipulatedafrequencyrangeforeachcommunicationsystem.Thisfrequencyrangeisalsocalledfrequencyband,andthefrequencyspectrumwidthofthefrequencybandisalsocalledworkingbandwidth.Forexample,theworkingbandwidthofGSMis25MHz,andbothWCDMAandCDMAare30MHz.

Themeaningofbandwidthinthefieldofhumanresources

Theso-called"bandwidth"referstothedifferencebetweenthemaximumandminimumwagesofeachgrade,anditbecomesthedistributionintervalofthesalaryvalue.Generallyspeaking,duetodifferentpositions,thecomplexityofskillsandresponsibilitiesinvolvedinthepositionorrankwillalsobedifferent.Therefore,thesalarybandwidthofeachrankshouldalsobedifferent(salarybandwidthshouldbeabletoreflectapositionOrthelevelofdifficultyrequiredfortheincumbentfromanewcomertoapersonwithoutstandingabilityandperformance).Iftheskillsandresponsibilitiesinvolvedinthepositionorrankcanbemasteredinashortperiodoftime,thesalarybandwidthofthislevelisnarrow;andiftheskillsandresponsibilitiesinvolvedinthepositionorrankneedtobelearnedforalongertime,continuetoimproveThechanceofbeingsmallerisalsosmaller,thecorrespondingbandwidthislarger.Accordingtothistheory,theprinciplethatchangersshouldadheretowhendesigninggradebandwidthis:thehigherthegrade,thegreaterthebandwidthshouldbe,becausethehigherthegrade,theslowertheincumbentwillbecompetent.

Thesignificanceofbandwidthindisplaysystems

Whenusingsinusoidalinputtostudythefrequencydynamiccharacteristicsofsensors,frequencycharacteristicsandphase-frequencycharacteristicsarecommonlyusedtodescribethedynamiccharacteristicsofsensors.TheimportantindicatorsareBandwidth,referredtoasbandwidth.

Bandwidthistheabbreviationofthefrequencywidthofthedisplayvideoamplifier.Itreferstothetotalnumberofpixels(Pixel)scannedbytheelectronguninonesecond,thatis,alllines(horizontaldirection))Thesumofthenumberofpixelsdisplayedonthescanlineandthefield(verticaldirection)scanline,inMHz.

Thedetailedcalculationformulaofbandwidth:B=r(x)×r(y)×V

• Brepresentsthebandwidthofthedisplay

  li>

• r(x)representsthenumberofpixelsoneachhorizontalscanline

• r(y)representsthehorizontalscanlineofeachframeNumber

• Vrepresentsthescreenrefreshratepersecond

• Thebandwidthisactuallytheamountofdatatransmittedperunittime