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7. Metafrash kai Diaxeiristes Diskwn

H gewmetria toy diskoy (me kefales, kylindroys kai ixnh) einai kati apo thn epoxh toy MFM kai toy RLL. Ekeines tis meres ayth htan h pragmatikothta. Shmera, me ta IDE h SCSI, kaneis den endiaferetai poia einai h `pragmatikh' gewmetria toys diskoy. Akomh, o ari8mos twn tomewn ana ixnos einai metablhtos: yparxoyn perissoteroi tomeis sto ejwteriko toy diskoy kai etsi den yparxei `pragmatikos' ari8mos tomewn ana ixnos. Anti8etws: h IDE entolh INITIALIZE DRIVE PARAMETERS (91h) xrhsimopoieitai gia na leei ston disko poses kefales kai tomeis/ixnos ypoti8etai oti exei. Einai arketa syxno na deite ena megalo monterno disko me 2 kefales na anaferei 15 h 16 kefales sto BIOS, enw to BIOS na anaferei 255 kefales sta programmata.

Gia ton xrhsth einai kalutero na exei to disko ws ena grammiko sunolo tomewn ari8mhmenoys ws 0, 1, ..., kai na afhsei ta hlektronika na broyn poy brisketai o ka8e tomeas ston disko. Ayth h grammikh ari8mhsh legetai LBA.

Etsi h genikh eikona einai ws ejhs: To DOS, h kapoios allos fortwths, mila sto BIOS, anaferontas ta (c,h,s). To BIOS ta metatrepei se LBA xrhsimopoiwntas thn ceutikh gewmetria poy xrhsimopoiei o xrhsths. An o diskos dextei to LBA tote ayth h timh xrhsimopoieitai gia thn prosbash. Alliws, metatrepetai pisw se (c',h',s') xrhsimopoiwntas th gewmetria poy anaferei o diskos kai etsi ginetai h prosbash.

Shmeiwste oti yparxei kapoia sugxysh sthn xrhsh toy `LBA': San oros poy perigrafei tis dynatothtes toy diskoy shmainei `Grammikh Diey8ynsiodothsh Temaxiwn = Linear Block Addressing' (se anti8esh me th diey8ynsiodothsh CHS). San oros sto BIOS Setup, perigrafei ena eidos metafrashs poy merikes fores kaleitai `boh8oumeno LBA = assisted LBA' - deite parapanw to ` The 8.4 GB limit '.

Kati paromoio symbainei otan o diskos den katalabainei to LBA alla to BIOS jerei thn metafrash. (Sto setup ayto synh8ws onomazetai `Large'.) Etsi to BIOS paroysiazei gewmetria (C,H,S) sto leitoyrgiko susthma kai xrhsimopoiei (C',H',S') otan epikoinwnei me ton elegkth. Synh8ws S = S', C = C'/N kai H = H'*N, opoye N einai h megaluterh dunamh toy duo poy sigoyreuei oti C' <= 1024 (etsi h xwrhtikothta stroggyleuetai pros ta katw se C' = C/N). Ayto epitrepei prosbash mexri 8.4 GB (7.8 GiB).

(H trith epilogh sto setup einai synh8ws h `Normal', opoy de ginetai kamia metafrash.)

Ean to BIOS den jerei ta `Large' h `LBA', tote yparxoyn luseis me programmata. Diaxeiristes diskwn opws oi OnTrack h EZ-Drive antika8istoun tis roytines diaxeirishs toy BIOS me tis dikes toys. Ayto synh8ws epitygxanetai me to na yparxei o kwdikas toy diaxeiristh sto MBR kai epakoloy8oys tomeis (to OnTrack onomazei ayton ton kwdika DDO: Dynamic Drive Overlay), wste na ekkineitai prin to leitoyrgiko susthma. Aytos einai o logos poy mporei na yparxoyn problhmata an kapoios jekinhsei to mhxanhma me disketa kai yparxei kai diaxeirisths diskoy.

To apotelesma einai ligo-polu to idio me th metafrash toy BIOS - alla an yparxoyn diaforetika leitoyrgika systhmata ston idio disko tote dhmioyrgountai polla problhmata.

To Linux yposthrizei to OnTrack apo thn ekdosh 1.3.14, kai to EZ-Drive apo thn ekdosh 1.3.29. Perissoteres leptomereies dinontai parakatw.


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