Me yasa haruffan ba a jere suke a EBCDIC?

An karɓi ma'aunin ASCII a cikin 1963, kuma yanzu da wuya kowa ya yi amfani da ɓoye wanda haruffa 128 na farko suka bambanta da ASCII. Duk da haka, har zuwa karshen karni na karshe, EBCDIC aka yi amfani da rayayye - daidaitattun rufaffiyar IBM mainframes da Soviet clones EC kwamfutoci. EBCDIC ya kasance farkon rikodi a cikin z/OS, daidaitaccen tsarin aiki don manyan firam na IBM Z na zamani.

Abin da ke kama ido nan da nan lokacin kallon EBCDIC shine cewa haruffan ba a jere suke ba: tsakanin I и J da tsakanin R и S akwai wuraren da ba a yi amfani da su ba (akan kwamfutar ES don waɗannan tazarar rarraba Haruffan Cyrillic). Wanene zai yi tunanin ya ɓoye haruffa tare da sarari mara daidaito tsakanin haruffa maƙwabta?

Sunan EBCDIC ("Extended BCDIC") yana nuna cewa wannan rikodin - sabanin ASCII - ba a ƙirƙira shi daga karce ba, amma dangane da ɓoyayyen BCDIC-bit shida, wanda aka yi amfani dashi tun daga lokacin. Farashin 704 (1954):

Babu daidaitattun koma baya nan da nan: fasalin da ya dace na BCDIC wanda ya ɓace a cikin canji zuwa EBCDIC shine lambobin 0-9 dace da lambobin 0-9. Koyaya, akwai gibi na lambobi bakwai tsakanin I и J kuma a cikin lambobi takwas tsakanin R и S sun riga sun je BCDIC. Daga ina suka fito?

Tarihin (E) BCDIC yana farawa lokaci guda tare da tarihin IBM - tun kafin kwamfutocin lantarki. An kafa IBM ne sakamakon hadewar kamfanoni hudu, wadanda suka fi samun ci gaba a fannin fasaha, shi ne Kamfanin Tabulating Machine, wanda Herman Hollerith, wanda ya kirkiro shi ne a shekarar 1896. tabulator. Tabulators na farko sun ƙidaya adadin katunan naushi da aka buga a takamaiman wuri; amma a cikin 1905 Hollerith ya fara samarwa desimal tabulators. Kowane kati don tabulator na goma ya ƙunshi filaye masu tsayi na sabani, kuma lambobin da aka rubuta a cikin waɗannan filayen a cikin nau'i na ƙima na yau da kullun an tattara su a kan dukkan bene. An ƙaddara ɓarnar taswirar zuwa filayen ta hanyar haɗa wayoyi a kan facin facin na tabulator. Misali, akan wannan katin bugu na Hollerith, adana a cikin Library of Congress, lambar 23456789012345678 an buga shi a fili, wanda ba a sani ba kamar yadda aka raba zuwa filayen:

Mai hankali zai iya lura cewa akan taswirar Hollerith akwai layuka 12 don ramuka, kodayake goma sun isa ga lambobi; kuma a cikin BCDIC, ga kowane ƙimar mafi mahimmancin rago biyu, lambobi 12 ne kawai ake amfani da su cikin 16 mai yiwuwa.

Tabbas, wannan ba daidaituwa ba ne. Da farko, Hollerith ya yi niyyar ƙarin layuka don “alamomi na musamman” waɗanda ba a haɗa su ba, amma kawai an ƙidaya su - kamar a cikin tabulators na farko. (A yau za mu kira su "filayen bit"). ya gano canji a cikin kowane alamomin ƙungiyar, kuma dole ne ma'aikacin ya sake rubuta jumloli daga allunan dijital akan takarda, sake saita allon, kuma ya ci gaba da tattara bayanai. Misali, lokacin ƙididdige ma'auni na lissafin kuɗi, ƙungiyar katunan zata iya dacewa da kwanan wata ko takwarorinsu ɗaya.

A shekara ta 1920, lokacin da Hollerith ya riga ya yi ritaya, an fara amfani da "tabulators buga rubutu", waɗanda aka haɗa su da nau'in teletype kuma suna iya buga juzu'i da kansu ba tare da buƙatar sa hannun mai aiki ba. Wahalar yanzu ita ce tantance abin da kowane lambobi da aka buga ke nufi. A cikin 1931, IBM ya yanke shawarar yin amfani da "alamomi na musamman" don nuna haruffa: alama a jere na 12 ya nuna harafin daga A to I, a cikin 11th - daga J to R, a sifili - daga S to Z. Sabuwar “tabulator na haruffa” na iya buga sunan kowane rukuni na katunan tare da jimla; a wannan yanayin, ginshiƙin da ba ya karye ya juya zuwa sarari tsakanin haruffa. Da fatan za a lura cewa S an tsara shi ta hanyar haɗin rami 0+2, kuma haɗin 0+1 ba a yi amfani da shi a asali ba don tsoron cewa ramuka biyu kusa da juna a cikin shafi ɗaya zai haifar da matsalolin inji a cikin mai karatu.

Yanzu zaku iya kallon teburin BCDIC daga kusurwa daban-daban:

Sai dai cewa 0 da sarari suna juyawa, mafi mahimmancin rago biyu suna bayyana "alama ta musamman" da aka buga cikin katin naushi don madaidaicin hali tun 1931; kuma mafi ƙanƙantar rago huɗu suna tantance lambar da aka buga cikin babban ɓangaren katin. Taimakon alamar & - / an ƙara su zuwa tabulators na IBM a cikin 1930s, kuma rikodin BCDIC na waɗannan haruffa yayi daidai da ramin da aka buga musu. Lokacin da ake buƙatar goyon baya ga adadin haruffan da ya fi girma, an buga jere na 8 a matsayin ƙarin "alama ta musamman" - don haka, ana iya samun ramuka har uku a cikin shafi ɗaya. Wannan tsarin katunan naushi ya kasance kusan baya canzawa har zuwa ƙarshen ƙarni. A cikin USSR, sun bar IBM's Latin da alamomin rubutu, kuma ga haruffa Cyrillic sun buga "alamomi na musamman" da yawa lokaci ɗaya a cikin layuka 12, 11, 0 - ba'a iyakance ga ramuka uku a cikin shafi ɗaya ba.

Lokacin da aka ƙirƙiri kwamfutar IBM 704, ba su daɗe da yin tunani game da yanayin shigar da ita ba: sun ɗauki rikodin da aka riga aka yi amfani da su a cikin katunan da aka buga a lokacin, kuma kawai “sanya shi a wurinsa.” A cikin 0, a lokacin sauyawa daga BCDIC zuwa EBCDIC, ƙananan nau'i-nau'i hudu na kowace alamar ba a canza su ba, ko da yake an jujjuya ragi masu girma. Don haka, tsarin katin naushi da Hollerith ya zaɓa a farkon karnin da ya gabata ya rinjayi gine-ginen dukkan kwamfutocin IBM, har zuwa da kuma haɗa da IBM Z.

source: www.habr.com