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6. Gewmetria diskoy, katatmhseis kai `epikaluceis'

Ean exete arketa leitoyrgika systhmata stoys diskoys sas, tote ka8ena xrhsimopoiei mia h perissoteres katatmhseis. Mia asymfwnia gia to poy briskontai aytes oi katatmhseis 8a exei katastrofika apotelesmata.

To MBR periexei enan pinaka katatmhsewn poy perigrafei poy briskontai oi (prwtarxikes) katatmhseis. Yparxoyne 4 eggrafes gia 4 prwtarxikes katatmhseis, me ka8e mia na einai

struct partition {
        char active;    /* 0x80: bootable, 0: not bootable */
        char begin[3];  /* CHS for first sector */
        char type;
        char end[3];    /* CHS for last sector */
        int start;      /* 32 bit sector number (counting from 0) */
        int length;     /* 32 bit number of sectors */
};
(opoy CHS einai Cylinder/Head/Sector).

Aytes oi plhrofories einai perittes: h perioxh ths katatmhshs dinetai kai apo to pedia twn 24-bit begin kai end, kai apo ta pedia twn 32-bit start kai length.

To Linux xrhsimopoiei mono ta pedia start kai length kai, etsi, mporei na diaxeiristei katatmhseis me to polu 2^32 tomeis, dhladh, katatmhseis to polu 2 TiB. Ayto einai 100 fores perissotero apo toys shmerinous diskoys, opote mallon 8a einai arketo gia ta epomeno 8 peripoy xronia. (Etsi, oi katatmhseis mporei na einai polu megales, alla yparxei o sobaros periorismos oti se ena ext2 susthma arxeiwn se mhxanhma me 32-bit akeraioys ena arxeio de mporei na einai megalutero apo 2 GiB.)

To DOS xrhsimopoiei ta begin kai end pedia, kai xrhsimopoiei thn BIOS INT13 klhsh gia prosbash sto disko, kai etsi mporei na dei diskoys to polu 8.4GB, akoma kai me BIOS poy kanei metafrash. (Oi katatmhseis de mporoun na einai panw apo 2.1 GB logw periorismwn toy FAT16 systhmatos). To idio isxuei kai gia ta Windows 3.11 kai WfWG kai Windows NT 3.* kai Novell NetWare.

Ta Windows 95 exoyn yposthrijh gia to Extended INT13, kai xrhsimopoioun eidikous tupoys katatmhsewn (c, e, f anti gia b, 6, 5) gia na deijoyn oti h katatmhsh 8a xrhsimopoih8ei etsi. Otan aytoi oi tupoi katatmhsewn xrhsimopoiountai, ta pedia begin kai end periexoyn ceutika stoixeia (1023/255/63). Ta Windows 95 OSR2 eishgagan to FAT32 susthma (tupoi katatmhsewn b or c), poy epitrepei katatmhseis to polu 2 TiB.

Ti einai ayta poy sas deixnei to fdisk gia `epikalyptomenes' katatmhseis, otan sthn pragmatikothta ola einai entajei; Yparxei kati 'la8os': an deite ta begin kai end pedia tetoiwn katatmhsewn, opws kanei to DOS, epikaluptontai. (Kai ayto de mporei na dior8w8ei, afou ta pedia ayta de mporoun na apo8hkeusoyn ari8mous kylindrwn anw toy 1024 - 8a yparxei panta 'epikalych' otan exete perissoteroys apo 1024 kylindroys.). Parola ayta, an deite ta start kai length pedia, opws kanei to Linux, kai ta Windows 95 sthn periptwsh katatmhsewn me tupo c, e h f, tote ola einai entajei. Etsi, agnohste tis proeidopoihseis toy otan to cfdisk einai ikanopoihmeno kai exete ena disko mono me Linux. Prosejte otan o diskos moirazetai me to DOS. Xrhsimopoihste tis entoles cfdisk -Ps /dev/hdx kai cfdisk -Pt /dev/hdx gia na deite ton pinaka katatmhsewn toy /dev/hdx.


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