Qhov sib txawv tseem ceeb ntawm qhov chaw nyob thiab qhov chaw nyob hauv lub cev yog CPU tsim qhov chaw nyob hauv lub sijhawm ua haujlwm thaum lub sijhawm ua haujlwm qhov chaw nyob yog qhov chaw nyob hauv lub cim xeeb.
Hauv cov ntsiab lus yooj yim, CPU tsim qhov chaw nyob lossis chaw nyob virtual. Los ntawm qhov kev xav ntawm qhov kev zov me nyuam uas tab tom khiav, ib yam khoom zoo li nyob ntawm qhov chaw nyob uas muab los ntawm qhov chaw nyob qhov laj thawj. Memory unit saib xyuas qhov chaw nyob ntawm lub cev. Ntxiv mus, nws tso cai rau nkag mus rau ib lub cim xeeb ntawm tes hauv lub cim xeeb loj los ntawm cov ntaub ntawv npav.
Qhov Chaw Nyob Logical yog dab tsi?
CPU tsim qhov chaw nyob qhov laj thawj. Los ntawm qhov kev xav ntawm qhov kev zov me nyuam uas tab tom khiav, ib yam khoom zoo li nyob ntawm qhov chaw nyob uas muab los ntawm qhov chaw nyob qhov laj thawj. Daim ntawv thov kev pab cuam uas khiav hauv lub computer tsis pom qhov chaw nyob. Lawv ib txwm ua haujlwm siv qhov chaw nyob qhov laj thawj. Qhov chaw nyob qhov chaw nyob yog cov txheej txheem ntawm qhov chaw nyob, ib qho kev pab cuam generates. Nws yog ib qho tsim nyog yuav tsum tau ua daim ntawv qhia qhov chaw nyob rau qhov chaw nyob ntawm lub cev ua ntej siv lawv. Cov cuab yeej kho vajtse Memory Management Unit (MMU) tswj cov txheej txheem kev kos duab no.
MMU Mapping Schemes
MMU ua raws li ob peb daim phiaj xwm phiaj xwm. Hauv cov phiaj xwm yooj yim tshaj plaws, tus nqi hauv kev tso npe hloov chaw yog ntxiv rau txhua qhov chaw nyob uas tsim los ntawm daim ntawv thov kev pab cuam ua ntej xa lawv mus rau lub cim xeeb. Kuj tseem muaj lwm txoj hauv kev los tsim cov duab kos. Chaw nyob khi (piv txwv li faib cov lus qhia thiab cov ntaub ntawv rau hauv qhov chaw nco) tuaj yeem tshwm sim ntawm peb lub sijhawm sib txawv.
Daim duab 01: Chaw nyob thiab lub cev
Ua ntej, nws tuaj yeem tshwm sim hauv lub sijhawm sau yog tias qhov chaw nco tiag tau paub ua ntej, thiab qhov no yuav tsim cov lej meej hauv lub sijhawm sau. Nws kuj tuaj yeem tshwm sim thaum lub sijhawm thauj khoom yog tias qhov chaw nco tsis paub ua ntej. Rau qhov no, re-locatable code yuav tsum tau tsim nyob rau hauv compile lub sij hawm. Tsis tas li ntawd, qhov chaw nyob khi tuaj yeem tshwm sim thaum lub sijhawm ua tiav. Qhov no yuav tsum muaj kev txhawb nqa kho vajtse rau kev qhia chaw nyob. Nyob rau hauv compile lub sij hawm thiab load sij hawm chaw nyob binding, logical thiab lub cev chaw nyob yog tib yam. Tab sis cov txheej txheem no txawv thaum qhov chaw nyob khi tshwm sim hauv lub sijhawm ua tiav.
Lub cev chaw nyob yog dab tsi?
Lub cim xeeb saib qhov chaw nyob ntawm lub cev lossis qhov chaw nyob tiag. Nws tso cai rau cov ntaub ntawv tsheb npav nkag mus rau ib lub cim xeeb tshwj xeeb hauv lub cim xeeb loj. MMU maps qhov chaw nyob logical rau qhov chaw nyob ntawm lub cev. Piv txwv li, siv cov phiaj xwm yooj yim tshaj plaws, uas ntxiv cov npe hloov chaw (xav tias tus nqi hauv daim ntawv teev npe yog y) tus nqi rau qhov chaw nyob, qhov chaw nyob qhov chaw nyob ntawm 0 txog x yuav daim duab qhia chaw nyob ntawm lub cev y mus rau x + y.
Tsis tas li ntawd, qhov no tseem hu ua qhov chaw nyob ntawm lub cev ntawm qhov kev zov me nyuam. Txhua qhov chaw nyob xav tau yuav tsum tau kos npe rau hauv qhov chaw nyob ua ntej lawv tuaj yeem siv tau.
Qhov txawv ntawm qhov chaw nyob qhov chaw thiab lub cev qhov chaw nyob yog dab tsi?
Logical Address vs Physical Address |
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| Logical chaw nyob yog qhov chaw nyob uas ib yam khoom zoo li nyob ntawm qhov kev xav ntawm kev ua tiav daim ntawv thov. | Lub cev chaw nyob yog qhov chaw nyob nco uas sawv cev rau hauv daim ntawv ntawm tus lej binary ntawm qhov chaw nyob hauv tsheb npav txhawm rau txhawm rau ua kom cov ntaub ntawv npav nkag mus rau ib qho chaw cia ntawm lub cim xeeb loj, lossis sau npe ntawm lub cim xeeb mapped I /O ntaus ntawv. |
| Visibility | |
| Tus neeg siv tuaj yeem pom qhov chaw nyob ntawm qhov program. | Tus neeg siv tsis tuaj yeem saib qhov chaw nyob ntawm qhov program. |
| CPU tsim qhov chaw nyob qhov laj thawj. | MMU suav qhov chaw nyob ntawm lub cev. |
| Accessibility | |
| Tus neeg siv tuaj yeem siv qhov chaw nyob kom nkag mus rau qhov chaw nyob ntawm lub cev. | Tus neeg siv tsis tuaj yeem nkag mus rau qhov chaw nyob ncaj qha. |
Summary – Logical Address vs Physical Address
Qhov sib txawv ntawm qhov chaw nyob thiab qhov chaw nyob hauv lub cev yog tias CPU tsim qhov chaw nyob qhov tseeb thaum qhov kev pab cuam ua haujlwm thaum qhov chaw nyob ntawm lub cev yog qhov chaw nyob hauv chav nco. Txhua qhov chaw nyob xav tau yuav tsum tau kos npe rau hauv qhov chaw nyob ua ntej MMU tuaj yeem siv tau. Lub cev thiab qhov chaw nyob yog tib yam thaum siv sijhawm sib sau thiab sijhawm thauj khoom lub sijhawm nyob ruaj khov, tab sis lawv txawv thaum siv sijhawm ua tiav qhov chaw nyob khi.
