{"id":96211,"date":"2020-10-09T07:42:43","date_gmt":"2020-10-09T05:42:43","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/pochemu-v-ebcdic-bukvy-idut-ne-podryad"},"modified":"2020-10-09T07:42:43","modified_gmt":"2020-10-09T05:42:43","slug":"pochemu-v-ebcdic-bukvy-idut-ne-podryad","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sl\/blog\/administrirovanie\/pochemu-v-ebcdic-bukvy-idut-ne-podryad","title":{"rendered":"Zakaj so v EBCDIC \u010drke razporejene tako, da niso zaporedne?","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Standard ASCII je bil sprejet leta 1963 in danes te\u017eko najdemo koga, ki bi uporabljal kodiranje, katerih prvih 128 znakov se razlikuje od ASCII. Kljub temu pa je do konca prej\u0161njega stoletja EBCDIC ostal aktivno uporabljen \u2013 standardno kodiranje za IBM glavne ra\u010dunalnike in njihove sovjetske klone ES EVM. EBCDIC ostaja osnovno kodiranje v z\/OS \u2013 standardnem operacijskem sistemu za sodobne IBM Z glavne ra\u010dunalnike.<\/p>\n

Prva stvar, ki pade v o\u010di ob pogledu na EBCDIC, je, da \u010drke niso razporejene zaporedno: med I<\/code> in J<\/code> in med R<\/code> in S<\/code> so ostale neizkori\u0161\u010dene pozicije (na ES EVM so med temi vrzeli razporedili<\/a><\/noindex> znake cirilice). Kdo bi lahko pomislil, da bi kodiral \u010drke z neenakomernimi presledki med sosednjimi \u010drkami?<\/p>\n

\"Zakaj<\/p>\n

Sam naziv EBCDIC («Extended BCDIC») sugeri\u0161e da je ova kodna stranica \u2014 za razliku od ASCII \u2014 nastala na osnovu \u0161estoslovne BCDIC kodne stranice, koja se koristila od IBM 704<\/a><\/noindex> (1954):<\/p>\n

\"Zakaj<\/p>\n

Neposredne zdru\u017eljive oblike ni: priro\u010dna zna\u010dilnost BCDIC, ki je izgubljena ob prehodu na EBCDIC, je bila, da \u0161tevilkam 0<\/code>\u20149<\/code> ustrezajo kode 0-9. Vendar so \u017ee obstajali premori s sedmimi kodi med I<\/code> in J<\/code> in z osmimi kodi med R<\/code> in S<\/code> v BCDIC. Kje so se torej pojavili?<\/p>\n

Istorija (E)BCDIC-a po\u010dinje u isto vreme kada i istorija IBM-a \u2014 dugo pre elektronskih ra\u010dunara. IBM je formiran spajanjem \u010detiri kompanije, od kojih je najtehnolo\u0161ki naprednija bila «Tabulating Machine Company», osnovana 1896. godine od strane Hermana Holeritha \u2014 izumitelja tabulatorja<\/a><\/noindex>. Prvi tabulatorji so preprosto \u0161teli \u0161tevilo perforiranih kartic, ki so bile prebite na dolo\u010denem mestu; toda leta 1905 je Hollerith za\u010del s proizvodnjo deseti\u010dnih<\/em> tabulatorjev. Vsaka kartica za deseti\u010dni tabulator je bila sestavljena iz polj poljubne dol\u017eine, in \u0161tevilke, zapisane v teh poljih v obi\u010dajni decimalni obliki, so se se\u0161tevale \u010dez celotno \u0161katlo. Razdelitev kartice na polja je bila dolo\u010dena s povezovanjem \u017eic na vezni plo\u0161\u010di tabulatorja. Na tej perforirani kartici Holleritha, hranjeni<\/a><\/noindex> v Kongresni knji\u017enici, je o\u010ditno izpisano \u0161tevilo 23456789012345678, neznano kako razdeljeno na polja:<\/p>\n

\"Zakaj<\/p>\n

Najbolj pozorni so lahko opazili, da ima kartica Holleritha 12 vrst odprtin, \u010deprav so za \u0161tevilke zadostne deset. V BCDIC pa za vsako vrednost najvi\u0161jih dveh bitov uporabljamo le 12 kod od 16 mo\u017enih.<\/p>\n

Naravno, to nije slu\u010dajna podudarnost. Holerith je prvobitno predvideo dodatne redove za «posebne oznake», koje se nisu sabirale, ve\u0107 su se samo brojale \u2014 poput onih u najranijim tabulatorima. (Danas bismo ih nazvali «bitnim poljima».) Pored toga, me\u0111u «posebnim oznakama» mogli su se postaviti group indicators: ukoliko su tokom tabulisanja bile potrebne ne samo kona\u010dne sume, ve\u0107 i me\u0111usume, tabulator se zaustavljao kada je otkrio promenu bilo kojeg od group indicators, a operater je morao da prepi\u0161e me\u0111usume sa digitalnih displeja na papir, da resetuje displej i ponovo zapo\u010dne tabulisanje. Na primer, prilikom brojanja knjigovodstvenih stanja grupa kartica mogla je odgovarati jednom datumu ili jednom partneru.<\/p>\n

Do 1920. godine, kada je Holerith ve\u0107 oti\u0161ao u penziju, do\u0161li su u upotrebu «\u0161tampani tabulatori», koji su bili povezani sa teletipom i mogli su sami \u0161tampati me\u0111usume, ne zahtevaju\u0107i intervenciju operatera. Slo\u017eenost je sada le\u017eala u tome da se utvrdi na \u0161ta se odnosi svaka od od\u0161tampanih brojki. 1931. godine IBM je odlu\u010dio da pomo\u0107u «posebnih oznaka» ozna\u010di slova: oznaka u 12. redu je ozna\u010davala slovo od A<\/code> do I<\/code>, v 11. vrstici \u2013 od J<\/code> do R<\/code>, v ni\u010dli \u2013 od S<\/code> do Z<\/code>. Novi «alfabetski tabulator» mogao je \u0161tampati naziv svake grupe kartica zajedno sa me\u0111usumama; pritom je neprobijeni stupac postajao razmak izme\u0111u simbola. Imajte na umu da S<\/code> je ozna\u010deno s kombinacijo lukenj 0+2, medtem ko je bila kombinacija 0+1 prvotno neuporabljena zaradi strahu, da bi lahko dve luknji v enem stolpcu povzro\u010dili mehanske te\u017eave pri bralniku.<\/p>\n

\"Zakaj<\/p>\n

Zdaj lahko na tabelo BCDIC pogledamo nekoliko druga\u010de:<\/p>\n

\"Zakaj<\/p>\n

Osim \u0161to su 0 i razmak zamenjeni mestima, gornja dva bita odre\u0111uju «posebnu oznaku», koja je od 1931. godine probijena u perforiranoj kartici za odgovaraju\u0107i simbol; a donja \u010detiri bita odre\u0111uju cifru, koja se probija u glavnom delu kartice. Podr\u0161ka simbolima & - \/<\/code> Se je pojavila v zavihkih IBM v 30. letih prej\u0161njega stoletja, in kodiranje teh simbolov v BCDIC ustreza prebadanjem kombinacij lukenj. Ko je bila potrebna podpora za \u0161e ve\u010d simbolov, so kot dodatno «posebno oznako» za\u010deli prebadajati vrstico 8 \u2014 tako je v enem stolpcu lahko bilo do treh lukenj. Ta format perforiranih kartic je ostal prakti\u010dno nespremenjen do konca stoletja. V ZSSR so ohranili IBM-ove kode latinice in lo\u010dila, za \u010drke cirilice pa so prebili kar nekaj «posebnih oznak» v vrsticah 12, 11, 0 \u2014 ne omejuju\u010d se na tri luknje v enem stolpcu.<\/p>\n

Ko so ustvarjali ra\u010dunalnik IBM 704, se dolgo niso ukvarjali s kodiranjem simbolov zanj: vzeli so kodiranje, ki se je \u017ee uporabljalo takrat v perforiranih karticah, in le 0 «postavili na svoje mesto». Leta 1964, ob prehodu z BCDIC na EBCDIC, so spodnje \u0161tiri bite vsakega simbola pustili nespremenjene, \u010deprav so nekoliko preme\u0161ali zgornje bite. Tako je format perforiranih kartic, ki ga je izbral Hollerith na za\u010detku prej\u0161njega stoletja, vplival na arhitekturo vseh ra\u010dunalnikov IBM, vklju\u010dno z IBM Z.<\/p>\n

Izvor: habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0421\u0442\u0430\u043d\u0434\u0430\u0440\u0442 ASCII \u0431\u044b\u043b \u043f\u0440\u0438\u043d\u044f\u0442 \u0432 1963, \u0438 \u0441\u0435\u0439\u0447\u0430\u0441 \u0432\u0440\u044f\u0434 \u043b\u0438 \u043a\u0442\u043e-\u043d\u0438\u0431\u0443\u0434\u044c \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u0443\u0435\u0442 \u043a\u043e\u0434\u0438\u0440\u043e\u0432\u043a\u0443, \u043f\u0435\u0440\u0432\u044b\u0435 128 \u0441\u0438\u043c\u0432\u043e\u043b\u043e\u0432 \u043a\u043e\u0442\u043e\u0440\u043e\u0439 \u043e\u0442\u043b\u0438\u0447\u0430\u043b\u0438\u0441\u044c \u0431\u044b \u043e\u0442 ASCII. \u0422\u0435\u043c \u043d\u0435 \u043c\u0435\u043d\u0435\u0435, \u0434\u043e \u043a\u043e\u043d\u0446\u0430 \u043f\u0440\u043e\u0448\u043b\u043e\u0433\u043e \u0432\u0435\u043a\u0430 \u0430\u043a\u0442\u0438\u0432\u043d\u043e \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u043b\u0430\u0441\u044c EBCDIC \u2014 \u0441\u0442\u0430\u043d\u0434\u0430\u0440\u0442\u043d\u0430\u044f \u043a\u043e\u0434\u0438\u0440\u043e\u0432\u043a\u0430 \u0434\u043b\u044f \u043c\u0435\u0439\u043d\u0444\u0440\u0435\u0439\u043c\u043e\u0432 IBM \u0438 \u0438\u0445 \u0441\u043e\u0432\u0435\u0442\u0441\u043a\u0438\u0445 \u043a\u043b\u043e\u043d\u043e\u0432 \u0415\u0421 \u042d\u0412\u041c. 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