Ga mafi yawan mutanen da suka yi amfani da kwamfutocin gida 8-bit a farkon shekarun 1980, yin amfani da kaset don adana shirye-shirye ya kasance ƙwaƙwalwar ajiya mai ɗorewa.Mutane masu arziki ne kawai za su iya samun fa'idodin faifai, don haka idan ba ku son ra'ayin jiran lambar ta ɗauka har abada, to kun yi rashin sa'a.Koyaya, idan kun mallaki Sinclair Spectrum, to zuwa 1983, kuna da wani zaɓi, Sinclair ZX Microdrive na musamman.
Wannan tsari ne wanda Sinclair Research ya haɓaka.Ainihin ƙaramin ƙaramin sigar keken tef ɗin madauki mara iyaka.Ya bayyana a cikin nau'i na kaset Hi-Fi mai waƙa 8 a cikin shekaru goma da suka gabata kuma yayi alƙawarin lokutan lodawa cikin sauri.Daƙiƙa da ƙaƙƙarfan ƙarfin ajiya fiye da 80 kB.Masu Sinclair na iya ci gaba da kasancewa tare da manyan yara a cikin duniyar kwamfutar gida, kuma za su iya yin hakan ba tare da karya banki da yawa ba.
A matsayina na matafiyi da ke dawowa daga sansanin ‘yan fashin teku a babban yankin, sakamakon barkewar cutar, gwamnatin Burtaniya ta bukaci a kebe ni na tsawon makonni biyu.Na yi shi a matsayin baƙo na Claire.Claire abokina ne kuma ya zama tushen ilimi.Babban 8-bit Sinclair hardware da mai tara software.Yayin da take magana game da Microdrive, ba kawai ta sayi wasu misalan tuƙi da software ba, har ma da tsarin dubawa da ainihin akwatin Microdrive.Wannan ya ba ni damar dubawa da wargaza tsarin tare da samar wa masu karatu abubuwan ban sha'awa game da wannan na'urar da ba a saba gani ba.
Ɗauki Microdrive.Naúrar ce mai auna kusan 80 mm x 90 mm x 50 mm kuma tana auna ƙasa da gram 200.Yana bin alamomin salo iri ɗaya na Rich Dickinson kamar ainihin maɓallin maɓallin roba na Spectrum.A gaba akwai buɗewar kusan 32 mm x 7 mm don shigar da kaset ɗin Microdrive, kuma a kowane gefen baya akwai mai haɗin PCB mai hanya 14 don haɗawa zuwa Spectrum da daisy-chaining ta hanyar bas na al'ada Wani Microdrive. yana ba da igiyoyin ribbon da masu haɗawa.Ana iya haɗa faifai har takwas ta wannan hanyar.
Dangane da farashi a farkon shekarun 1980, Spectrum na'ura ce mai ban sha'awa, amma farashin aiwatar da shi shine ya biya kadan don ginanniyar ƙirar kayan masarufi fiye da tashoshin bidiyo da kaset ɗinta.Bayan shi akwai mai haɗin baki, wanda a zahiri yana fallasa manyan motocin bas na Z80, yana barin duk wani ƙarin mu'amala da aka haɗa ta hanyar haɓakawa.Mai mallakar Spectrum na yau da kullun na iya mallakar adaftar joystick na Kempston ta wannan hanyar, mafi kyawun misali.Spectrum ba shakka ba a sanye shi da mai haɗin Microdrive ba, don haka Microdrive yana da nasa dubawa.Sinclair ZX Interface 1 naúrar ce mai siffa mai siffa wacce ke haɗawa da mai haɗin gefuna akan Spectrum kuma an murƙushe shi zuwa ƙasan kwamfutar.Yana ba da hanyar sadarwa ta Microdrive, tashar tashar RS-232, mai sauƙin haɗin haɗin LAN ta amfani da jack 3.5 mm, da Replica na mai haɗa gefen gefen Sinclair tare da ƙarin musaya da aka saka.Wannan masarrafa tana dauke da ROM wanda yake zayyana kansa zuwa Spectrum na ciki ROM, kamar yadda muka yi nuni da lokacin da samfurin Spectrum ya bayyana a Cibiyar Tarihin Kwamfuta ta Cambridge, kamar yadda muka sani, ba a kammala shi ba kuma wasu ayyukan da ake sa ran ba a aiwatar da su ba.
Yana da ban sha'awa don magana game da hardware, amma ba shakka, wannan shine Hackaday.Ba wai kawai kuna son ganinsa ba, kuna son ganin yadda yake aiki.Yanzu lokaci ya yi da za a sake haɗawa, za mu fara buɗe naúrar Microdrive kanta.Kamar dai Spectrum, saman na'urar an rufe shi da farantin allumini mai baƙar fata mai alamar tambarin Spectrum, wanda dole ne a raba shi a hankali da sauran ƙarfin abin da ya rage na 1980s don fallasa nau'ikan dunƙule guda biyu waɗanda ke tabbatar da sashin sama.Kamar Spectrum, yin hakan yana da wahala ba tare da lankwasa aluminum ba, don haka ana buƙatar wasu ƙwarewa.
Ɗaga babban ɓangaren kuma saki LED ɗin direba, na'urar injiniya da allon kewayawa suna bayyana a fagen hangen nesa.Kwararrun masu karatu nan da nan za su lura da kamanceceniya da ke tsakaninsa da kaset mai sauti 8 mafi girma.Ko da yake wannan ba asalin tsarin ba ne, yana aiki a irin wannan hanya.Tsarin kanta yana da sauqi qwarai.A gefen dama akwai ƙananan maɓalli wanda ke hankalta lokacin da tef ɗin ya cire alamar kariya ta rubutu, kuma a gefen hagu akwai ramin mota tare da abin nadi na capstan.A ƙarshen kasuwancin tef ɗin akwai kan tef, wanda yayi kama da abin da zaku iya samu a cikin rikodin kaset, amma yana da jagorar tef ɗin kunkuntar.
Akwai PCB guda biyu.A bayan kan tef ɗin akwai ULA na al'ada 24 (Uncommitted Logic Array, ainihin magabacin CPLD da FPGA a cikin 1970s) don zaɓar da sarrafa kayan aiki.An haɗa ɗayan zuwa kasan rabin gidajen da ke da haɗin haɗin haɗin sadarwa guda biyu da na'ura mai sauyawa na lantarki.
Tef ɗin yana da 43 mm x 7 mm x 30 mm kuma ya ƙunshi tef ɗin madauki mai ci gaba tare da tsawon mita 5 da tsayin 1.9 mm.Ba na zargin Claire don rashin barin ni in buɗe ɗaya daga cikin tsoffin katun nata, amma an yi sa'a, Wikipedia ya ba mu hoton harsashi tare da rufe saman.Kamanceceniya tare da tef ɗin waƙa 8 ya bayyana nan da nan.Capstan na iya kasancewa a gefe ɗaya, amma madaidaicin tef ɗin ana mayar da shi zuwa tsakiyar reel ɗaya.
Littafin littafin microdrive na ZX yayi da'awar cewa kowane kaset na iya ɗaukar 100kB na bayanai, amma gaskiyar ita ce da zarar an yi amfani da wasu kari, za su iya ɗaukar kusan 85 kB kuma su ƙaru zuwa fiye da 90 kB.Yana da kyau a ce ba su ne mafi amintattun kafofin watsa labarai ba, kuma kaset ɗin daga ƙarshe ya miƙe har ta kai ga an daina karanta su.Ko da Manual na Sinclair yana ba da shawarar tallafawa kaset ɗin da aka saba amfani da su.
Bangare na ƙarshe na tsarin da za a wargaje shi shine interface 1 kanta.Ba kamar samfurin Sinclair ba, ba shi da wani sukurori da ke ɓoye a ƙarƙashin ƙafar roba, don haka baya ga aikin dabarar raba saman gidaje daga mai haɗin gefen Spectrum, yana da sauƙin kwancewa.A ciki akwai kwakwalwan kwamfuta guda uku, Texas Instruments ROM, kayan aikin ULA na duniya maimakon aikin Ferranti wanda Spectrum kanta ke amfani da shi, da ɗan dabaru na 74.ULA ya haɗa da duk da'irori ban da na'urori masu hankali da aka yi amfani da su don tuƙi RS-232, Microdrive, da serial bas na cibiyar sadarwa.Sinclair ULA sananne ne don yawan zafi da dafa abinci, wanda shine nau'in mafi rauni.Ba za a iya amfani da keɓancewa a nan da yawa ba, saboda ba a shigar da na'urar radiyo ta ULA ba, kuma babu alamar zafi akan harsashi ko kewaye.
Jumla ta ƙarshe ta rarrabuwa yakamata ta zama jagorar, wanda shine ƙayyadaddun ƙayyadaddun ƙaƙƙarfan rubutu mai kyau wanda zai iya ba da zurfin fahimtar tsarin da yadda aka haɗa shi cikin fassarar BASIC.Ƙarfin sadarwar yana da ban sha'awa musamman saboda ba a cika amfani da shi ba.Ya dogara da kowane Spectrum a cikin hanyar sadarwa don ba da umarni don sanya wa kansa lamba idan ya fara, saboda babu Flash ko makamancin haka a cikin jirgi.An yi niyya ne da farko don sanya kasuwar makarantar a matsayin mai fafatawa ga Acorn's Econet, don haka ba abin mamaki ba ne cewa BBC Micro ta sami kwangilar makaranta da gwamnati ke goya baya maimakon injin Sinclair.
Tun daga shekarar 2020, duba baya ga wannan fasahar kwamfuta da aka manta da ita kuma ku duba duniyar da ake loda ma’adanin ajiya mai nauyin kB 100 a cikin kusan dakika 8 maimakon ‘yan mintoci na loda tape.Abin da ke daure kai shi ne, Interface 1 ba ya hada da parallel printer interface, domin duba da cikakken tsarin Spectrum, ba shi da wahala a ga cewa ta zama wadatacciyar kwamfuta mai samar da ofis a cikin gida a yau, gami da farashinta.Sinclair suna sayar da nasu firintocin zafin jiki, amma har ma masu sha'awar Sinclair masu tauraro da kyar ba za su iya kiran firinta na ZX wani sabon abu ba.
Gaskiyar ita ce, kamar duk Sinclairs, ta kasance wanda aka azabtar da Sir Clive na almara na rage tsadar farashi da kuma ƙwararrun ikon ƙirƙirar dabarar da ba za ta yiwu ba daga abubuwan da ba a zata ba.Sinclair ya haɓaka Microdrive gaba ɗaya a cikin gida, amma wataƙila ya yi kadan, ba abin dogaro ba ne, kuma ya yi latti.Apple Macintosh na farko sanye take da floppy drive ya fito a farkon 1984 a matsayin samfurin zamani na ZX Microdrive.Ko da yake waɗannan ƙananan kaset ɗin sun shiga na'urar Sinclair maras lafiya 16-bit QL, ya zama gazawar kasuwanci.Da zarar sun sayi kadarorin Sinclair, Amstrad zai ƙaddamar da Spectrum tare da faifan floppy inch 3, amma a lokacin Sinclair microcomputers ana siyar da su azaman consoles na wasan.Wannan ɓarna ce mai ban sha'awa, amma wataƙila yana da kyau a bar tare da tunanin farin ciki na 1984.
Ina matukar godiya ga Claire don amfani da kayan aikin a nan.Idan kuna mamaki, hoton da ke sama yana nuna nau'ikan nau'ikan abubuwa daban-daban, gami da kayan aiki da kayan aikin da ba su aiki ba, musamman naúrar Microdrive da aka wargaje gaba ɗaya rukunin ya gaza.Ba ma son cutar da kayan aikin kwamfuta na baya ba dole ba akan Hackaday.
Na yi amfani da Sinclair QL sama da shekaru bakwai, kuma dole ne in faɗi cewa microdrives ɗin su ba su da rauni kamar yadda mutane ke faɗi.Sau da yawa ina amfani da su don aikin gida na makaranta, da sauransu, kuma ban taɓa rasa kowane takarda ba.Amma hakika akwai wasu na'urori na "zamani" waɗanda suka fi aminci fiye da na asali.
Game da Interface I, yana da ban mamaki sosai a ƙirar lantarki.Serial tashar jiragen ruwa ne kawai matakin adaftan, kuma RS-232 yarjejeniya ana aiwatar da software.Wannan yana haifar da matsaloli yayin karɓar bayanai, saboda injin yana da lokacin ɗan tasha kawai don yin duk abin da ya dace da bayanan.
Bugu da ƙari, karatun daga tef yana da ban sha'awa: kuna da tashar jiragen ruwa na IO, amma idan kun karanta daga gare ta, dubawa zan dakatar da na'ura mai sarrafawa har sai an karanta cikakken byte daga tef (wanda ke nufin cewa idan kun manta Kunna motar tef). kuma kwamfutar za ta rataya).Wannan yana ba da damar aiki tare da sauƙi na mai sarrafawa da tef ɗin, wanda ya zama dole saboda samun damar zuwa toshe na 16K na biyu (na farko yana da ROM, na uku da na huɗu suna da ƙarin ƙwaƙwalwar ajiya na nau'ikan 48K), kuma saboda buffer microdrive Yana faruwa. zama a wannan yanki, don haka ba shi yiwuwa a yi amfani da madaukai masu lokaci kawai.Idan Sinclair yana amfani da hanyar samun dama kamar wacce aka yi amfani da ita a cikin Inves Spectrum (wanda ke ba da damar da'irar bidiyo da na'ura mai sarrafawa don samun damar RAM na bidiyo ba tare da wani hukunci ba, kamar [a cikin Apple), to, kewayawar keɓancewar zai iya zama mai sauƙi da yawa.
Spectrum yana da lokaci mai yawa don aiwatar da bytes ɗin da aka karɓa, muddin na'urar a ɗayan ƙarshen tana aiwatar da sarrafa kwararar hardware daidai (ga wasu (duk?) chips ɗin motherboard “SuperIO” * ba * halin da ake ciki ba. yin kuskure kafin fahimtar wannan kuma canza zuwa tsohuwar adaftar adaftar kebul na USB, Na yi mamakin cewa Just Worked yayi aiki a karon farko)
Kusan RS232.Na sami 115k kuskure gyara da 57k abin dogara bit bumping ba tare da kuskure yarjejeniya yarjejeniya.Sirrin shine ci gaba da karɓar har zuwa 16 bytes bayan jefar da CTS.Lambar ROM ta asali ba ta yi wannan ba, kuma ba za ta iya sadarwa tare da UART na "zamani" ba.
Wikipedia ya ce 120 kbit/sec.Game da ƙayyadaddun ƙa'idar, ban sani ba, amma na san tana amfani da shugaban tef ɗin sitiriyo, kuma ajiyar bit ɗin “marasa daidaituwa”.Ban san yadda zan bayyana shi a cikin Turanci ba… ɓangarorin da ke cikin waƙa ɗaya suna farawa a tsakiyar bits a ɗayan waƙar.
Amma bincike mai sauri na sami wannan shafin, inda mai amfani ya haɗa oscilloscope zuwa siginar bayanai, kuma da alama FM modulation ne.Amma QL ne kuma bai dace da Spectrum ba.
Ee, amma da fatan za a tuna cewa hanyar haɗin tana magana game da Sinclair QL microdrives: kodayake a zahiri iri ɗaya ne, suna amfani da tsarin da ba su dace ba, don haka QL ba zai iya karanta kaset ɗin tsarin Spectrum ba, kuma akasin haka.
Bit daidaitacce.Ƙungiyoyin bytes an haɗa su tsakanin waƙa 1 da waƙa 2. Yana da ɓoyayyen ɓoyayyen abu biyu.fm da ake samu akan katunan kuɗi.Ƙaddamarwa tana sake haɗa bytes a cikin hardware, kuma kwamfutar tana karanta bytes kawai.Adadin bayanan asali shine 80kbps kowace waƙa ko 160kbps duka biyun.Ayyukan aiki yayi kama da faifan floppy na wancan zamanin.
Ban sani ba, amma akwai labarai da yawa game da cikakken rikodi a lokacin.Domin amfani da mai rikodin kaset na yanzu, ana buƙatar sautunan sauti.Amma idan kun canza kan tef ɗin shiga kai tsaye, zaku iya ciyar da su kai tsaye tare da ikon DC kuma kai tsaye haɗa abin faɗakarwa na Schmitt don sake kunnawa.Don haka kawai yana ciyar da siginar siginar tef ɗin.Kuna iya samun saurin gudu ba tare da damuwa game da matakin sake kunnawa ba.
Tabbas ana amfani da shi a cikin duniyar “babban firam”.A koyaushe ina tsammanin ana amfani da shi a cikin wasu ƙananan shirye-shiryen kwamfuta, kamar “floppy disks”, amma ban sani ba.
Ina da QL tare da 2 micro-drives, wanda gaskiya ne, aƙalla QL ya fi aminci fiye da yadda mutane ke faɗi.Ina da ZX Spectrum, amma babu microdrives (ko da yake ina son su).Abu na baya-bayan nan da na samu shi ne yin wasu ci gaban giciye.Ina amfani da QL azaman editan rubutu da canja wurin fayiloli zuwa Spectrum wanda ke haɗa fayiloli ta hanyar serial (Ina rubuta direban firinta don shirin ZX Spectrum PCB Designer, wanda zai haɓaka da Saka pixels zuwa ƙuduri na 216ppi don kada waƙar ba ta daɗe. bayyana jagged).
Ina son QL dina da software ɗin sa, amma dole ne in ƙi microdrive ɗin sa.Sau da yawa ina karɓar kurakuran "MUMMUNAN KO CANJIN" bayan tashi daga aiki.Abin takaici da rashin dogaro.
Na rubuta takardar BSc ta kimiyyar kwamfuta akan ta 128Kb QL.Quill zai iya adana kusan shafuka 4 kawai.Ban taba kuskura in zubar da ragon ba saboda zai fara girgiza micro drive kuma kuskuren zai tashi nan ba da jimawa ba.
Na damu sosai game da amincin Microdrive wanda ba zan iya yin rikodin kowane zaman gyara akan kaset ɗin Microdrive guda biyu ba.Duk da haka, bayan rubuta dukan yini, na ajiye sabon babi na da gangan a ƙarƙashin sunan tsohon babi, don haka na sake rubuta aikina a ranar da ta gabata.
"Ina ganin ba laifi, aƙalla ina da madadin!";Bayan canza tef ɗin, na tuna cewa ya kamata a ajiye aikin yau akan madadin kuma a sake rubuta aikin ranar da ta gabata cikin lokaci!
Har yanzu ina da QL dina, kusan shekara guda da ta gabata, na yi nasarar amfani da ƙaramin akwati mai shekaru 30-35 don adanawa da loda shi.
Na yi amfani da floppy drive na ibm pc, adaftar ce a bayan bakan, yana da sauri da daɗi.(kwatanta shi da tef dare da rana)
Wannan ya dawo da ni.A lokacin na yi hacking komai.Ya ɗauki mako guda don shigar da Elite akan Microdrive kuma bari LensLok koyaushe ya zama rawar AA.Lokacin loading Elite shine 9 seconds.An kashe fiye da minti ɗaya akan Amiga!Yana da asali juji na memory.Na yi amfani da katsewa na yau da kullun don saka idanu int 31 (?) don wutar farin ciki ta Kempston.LensLok yana amfani da katsewa don shigar da madannai, don haka kawai ina buƙatar matsi a cikin lambar don sa ta kashe ta atomatik.Elite kawai ya bar kusan bytes 200 ba a yi amfani da su ba.Lokacin da na ajiye shi tare da *”m”,1, taswirar inuwar inuwar 1 ta hadiye katsewata!Kai.shekaru 36 da suka gabata.
Na dan yaudari… Ina da Discovery Opus 1 3.5-inch floppy disk akan Speccy na.Na gano cewa godiya ga wani hatsarin farin ciki a ranar da Elite ya fado yayin lodawa, zan iya ajiye Elite zuwa faifan floppy… kuma sigar 128 ce, babu makullin ruwan tabarau!sakamako!
Yana da ban sha'awa cewa kimanin shekaru 40 bayan haka, floppy diski ya mutu kuma tef ɗin har yanzu yana wanzu:) PS: Ina amfani da ɗakin karatu na tef, kowanne yana da 18 drives, kowane drive zai iya samar da gudun 350 MB / s;)
Ina so in san idan kun kwakkwance adaftar kaset, za ku iya amfani da kan maganadisu don loda bayanai cikin kwamfuta ta microdrive?
Kawukan suna kama da juna, idan ba iri ɗaya ba (amma "kai mai gogewa" ya kamata a haɗa shi cikin tsari), amma tef ɗin a cikin microdrive ya fi kunkuntar, don haka dole ne ku gina sabon jagorar tef.
"Mutane masu arziki ne kawai za su iya samun kayan aikin diski."Wataƙila a Burtaniya, amma kusan kowa a Amurka yana da su.
Na tuna farashin PlusD + faifan diski + adaftar wutar lantarki, a cikin 1990, kusan 33.900 pesetas ne (kimanin Yuro 203).Tare da hauhawar farashin kaya, yanzu Yuro 433 (US $512).Wannan kusan daidai yake da farashin cikakkiyar kwamfuta.
Na tuna cewa a cikin 1984, farashin C64 ya kasance dalar Amurka 200, yayin da farashin 1541 ya kasance dalar Amurka 230 (a gaskiya ya fi kwamfutar, amma la'akari da cewa yana da 6502 na kansa, wannan ba abin mamaki ba ne).Waɗannan biyun da arha TV har yanzu ba su kai kashi ɗaya cikin huɗu na farashin Apple II ba.Akwatin faifan faifai 10 ana sayar da ita akan $15, amma farashin ya ragu tsawon shekaru.
Kafin in yi ritaya, na yi amfani da ƙwararrun masana’antu da kera injina a arewacin Cambridge (Birtaniya), wanda ya kera dukkan injunan da ake amfani da su don kera mashinan Microdrives.
Ina tsammanin a farkon shekarun 1980, rashin tashar tashar jiragen ruwa mai jituwa da ta dace da centronics ba babban abu ba ne, kuma masu bugawa na yau da kullum sun kasance na kowa.Bayan haka, Uncle Clive yana son siyar da ku ZX FireHazard… firinta mai kyau.Huma mara iyaka da ƙamshin ozone yayin da yake motsawa ƙasa da takarda mai launin azurfa.
Micro drives, sa'a na ya yi muni sosai, na cika sha'awar su a lokacin da suka fito, amma sai bayan wasu 'yan shekaru na fara karban kayan aiki mai rahusa daga kayan na biyu, kuma ban yi ba. sami wani hardware.Na ƙare da 2 tashar jiragen ruwa 1, 6 micro-drives, wasu kuloli da aka yi amfani da su ba da gangan ba, da akwati na 30 sababbin kutunan murabba'i na 3rd, idan zan iya yin kowannensu a cikin kowane haɗin 2 × 6 Ina jin haushi sosai lokacin da nake aiki a ciki. wuri guda.Yawanci, da alama ba a tsara su ba.Ban taɓa yin tunani game da shi ba, ko da na sami taimako daga ƙungiyoyin labarai lokacin da na shiga kan layi a farkon 90s.Koyaya, yanzu da nake da kwamfutoci na “ainihin”, na sami tashar tashar jiragen ruwa ta yi aiki, don haka sai na adana musu abubuwa ta hanyar kebul na modem mara amfani kuma na kunna wasu tashoshi na bebe.
Shin akwai wanda ya rubuta shirin zuwa "pre-mike" kaset ta hanyar gudanar da su cikin madauki kafin yunƙurin tsara su?
Ba ni da micro drive, amma na tuna karanta shi a cikin ZX Magazine (Spain).Lokacin da na karanta, ya ba ni mamaki!
Ina da alama in tuna cewa firinta na lantarki ne, ba thermal ba… Ina iya yin kuskure.Mutumin da na yi aiki a kan haɓaka software da aka saka a ƙarshen 80s ya toshe ɗayan tef ɗin zuwa Speccy kuma ya toshe na'urar EPROM zuwa tashar baya.Idan ka ce wannan amfani da ɗan banza ne zai zama rashin fahimta.
Haka kuma.An lulluɓe takardar da ɗan ƙaramin ƙarfe, kuma na'urar bugawa tana jan stylus ɗin karfe.Ana haifar da bugun jini mai ƙarfi don kawar da murfin ƙarfe a duk inda ake buƙatar baƙar fata.
Lokacin da kake matashi, ZX interface 1 tare da RS-232 dubawa ya sa ka ji kamar "sarkin duniya".
A haƙiƙa, Microdrives gaba ɗaya sun wuce kasafin kuɗi na (mafi ƙarancin).Kafin in sadu da wannan mutumin da ya sayar da wasannin satar fasaha LOL, babu wanda na sani.A cikin hangen nesa, yakamata in sayi Interface 1 da wasu wasannin ROM.Da wuya kamar haƙoran kaza.
Lokacin aikawa: Juni-15-2021