So what ex­actly is real ad­dress­ing mode?

OpenSource For You - - OPEN GURUS INSIGHT -

As men­tioned ear­lierI when an x86 sys­tem is pow­ered up or UHsHW, LW Ls Ln UHDO PRGH. ,I yRX wRnGHUHG wKy WKLs Ls sR, LW’s be­cause in the real ad­dress­ing modeI an x86 sys­tem be­comes back­ward com­pat­i­ble with all pre­vi­ous x86 chipsI and thus al­lows the BIlS and other pre­his­toric soft­ware to run. 8M86I the nRWDEOH 16-ELW PLFURSURFHssRU IURP ,nWHO DnG WKH vHUy fiUsW wLWK the x86-ar­chi­tec­tureI while im­ple­ment­ing mem­ory seg­men­ta­tion, op­er­ates only in real mode. Soft­wareI in real modeI can di­rectly ac­cess all mem­o­ryI ILl ad­dresses and hard­ware pe­riph­er­als; how­ev­erI the mem­ory that can be ad­dressed is limited to only OOM bytesI i.e.I only 1 MB of mem­ory can be ad­dressed. cur­therI the en­tire 1 MB of mem­ory can­not be ac­tive at the same time but par­ti­tions of 64 KB seg­ments can. bach seg­ment has its own start­ing ad­dress and is num­bered from MMMMMH to cc­c­ccH.

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