Introduction to Computer CSC 101 (PUMS) PDF

I NTRODUCTI ONTOCOMPUTERCSC101( PUMS) Comput ers ar e embedded i n ev ery thi ng f...

I NTRODUCTI ONTOCOMPUTERCSC101( PUMS) Comput ers ar e embedded i n ev ery thi ng f rom camer as,mi crowav e ov ens t o aut omobi l es butmostoft he t ime t heyar e hi dden f rom si ght.Theyper for m cal cul ati onorcomput ati onsaut omat ical l y. Per sonalcomput err efer stoasepar atev isi blecomput ermachi neser vingasi ngl e per son. Techni cal l yspeaki ng, comput eri sanel ect roni cdev icet hataut omat ical l ypr ocesses i nput( dat a)i n accor dance wi tht he pr ogr am ofi nst ruct ions st ored wi thi nthe comput erandt henpr ovi dest her esul tsi nausef ulf orm( inf ormat ion). Comput erconsi stsofhar dwar eandsof twar e.Har dwar ear ethosepar tsoft he comput erwecanf eelandt ouchwhi l ethesof twar ear ethepr ogr ams,i nst ruct ions anddat athatcanonl ybeseenbutnotf elt. Har dwar ecomponent s: ( 1)I /O( 2)Mai nmemor y(3)CPU( 4)Secondar yst orage. TheI /Ost andsf ori nputandout put.Inputi sthatpar tthr oughwhi cht hecomput er r ecei vespr ogr ams,dat aandi nst ruct ionwhi l eint heout put ,thecomput ersendsout i nfor mat ionort hepr ocesseddat a. Mai nmemor y:Themai nmemor yconsi stsoft heROM ( readonl ymemor y)andt he RAM ( random accessmemor y).I nst ruct ionanddat ast oredi ntheRAM i str ansi ent becauseofv olat il enat ureoft hedev ice.Howev er, theonei nthesecondar ymemor y i smor eper manent.RAMsi ncl udesst ati c(SRAM) ,dy nami c(DRAM) ,doubl edat a ( DDRAM).Exampl eofsecondar ymemor iesar ehar ddi sk,f lash,sol i d-st atedev ice, f loppydi sket tes, DVD, magnet ict apeCDRW, CD- ROM, WORM. Thespeedoft hemai nmemor yismeasur edi nuni tscal l edHer tz,whi chsi mpl y meansonecy clepersecondoft hesy stem cl ock.Thecl ocki sani nter naldev icet hat r egul atest hespeedatwhi chmemor iesandpr ocessor sfunct ions.Ot heruni tsof cl ockar eKi l oher tzKHz, Megaher tzMHzandGi gaher tzGHz.OneKHzi s1t housand cy clepersecond,MHzi s1mi l li oncy clepersecond,GHzi s1bi l li oncy clesper second. 1 TheCPUot her wisecal l edt hecent ralpr ocessi nguni tist hecomput ati onalpar tofa comput er.Somecommonpr ocessornamesar eInt el,AMD,At hal on,I tani um,Power PCG5andXenon.I ntel hasot herv ari ant sPent ium, Cel eronet c. The i tems f orpr ocessi ng byt he comput erpr ocessorar e nor mal l yfet ched or col l ect edf rom t hemai nmemor yespeci all y,t heRAM.Pr ocessor soper ati onsar e al someasur edi nter msofcl ockspeedbutt hist imei nnumberofmi l li oni nst ruct ions perseconds( mips).Thehi ghert hecl ockspeedt hef ast ert hecomput erpr ocessor. Theyal sohav ethesameuni tsl i ket hemai nmemor yasKHz, MHzandGHz. Tr end: Processor sspeeddoubl esappr oxi mat elyev ery18mont hs. Comput erSof twar e:Thesear epr ogr amsorI nst ruct ionst hatenabl ethehar dwar e communi cat etot he comput eruser.Wi thoutoper ati ng sy stem sof twar e(OPS) comput ercannotf unct ion. Ty pesofSof twar e:Twot ypesofsof twar eexi sts:sy stem sof twar eandappl i cat ion sof twar e.Sy stem sof twar eli ket heoper ati ngsy stem ar ehostpr ogr amst hatt he comput ermanuf act urer sinst allbef oresel l ingt hecomput ert oenabl eitf unct ion. Appl i cat ionsof twar ear ethosepr ogr amsi nst all edbyt hecomput eruserf orcar ryi ng outv ari ousf unct ionsl i kewor dpr ocessi ng, drawi ngs, cal cul ati ons, imagepr ocessi ng, pr esent ati onset c. Funct ionsoft heOper ati ngSy stem 1.Mai ntai nfi l esy stem di rect ori es, fol der s,subdi rect ori es 2.Managesmemor y 3.Pr ovi desGUI 4.Hostl evel secur it y-useraccount s,passwor ds, local fir ewal l 5.Ensur esi ntegr it yofsev eral progr amst hatr unssi mul taneousl yandact ive. Comput erasaSy stem:A comput eri scal l edasy stem becauseofcol l abor ati ve oper ati ngnat urebet weent hecomput erhar dwar eandi tsoper ati ngsy stem. Comput eroper ati on: fet ch- decode- execut ecy cle. 2 I nst ruct ions f etched f rom mai n memor yconst it ute pr ogr am and dat athatar e pr epar edf orexecut ionbyt heCPU.Thesear emachi nel anguagei nst ruct ionsand t heyar eusual l ycodedi nthef orm conv eni entf orapar ti cul armachi ne.Thef etch- decode- execut ecy cler efer stot her epeat edf ormi nwhi chCPUobt ainsi nst ruct ion anddat afr om memor yandexecut esi t. Comput ert ypes:Anal og( cont inuous) ,Di git al( discr ete)andHy bri d(cont inuous+ di scr ete) Anal ogdev icesar ebasedoncont inuousl yvar yingsy stemswhi l edi git aldev icesar e basedonf ixeddi scr etenumberofal ter nat ionse. g. TheEl evat ori sanal og,t he st air wayi sdi scr ete, amot ionpi ctur eisdi scr ete( dif fer entf rames)pl ayedatt her ate of30f ramespersecondgi vi ngt hei l lusi onofcont inuousmot ion. Hy bri disbot hdi git alandanal ogeg.Speedomet er,wr ist wat ches,anal ogt odi git al conv ert er( ADC) ,di git alt oanal ogconv ert er( DAC). HowComput ersshowI mages, Col our sandpl aySound I magesi nacomput erVDU( moni tor )ar edi spl ayedi nagr idofsmal lrect angul ar f igur escal l edpi xel s(pi ctur eel ement s). Cur rent lyt oday ’scomput erVDUmeasur es17i nchesdi agonal l ywi thv isi bler egi onof 1280pi xel shor izont all yby1024pi xel sver ti cal l y. Col our sandi ntensi tyofgr aphi cali magesandr esol uti ondi ff erdependi ngont he di git ali zat iont echni quet heVDUuses.Onecommonl yusedt echni quei sthemi xtur e ofr ed, greenandbl ue( RGB)col our sdi git izedbyst ori ngv ary ingnumberr epr esent ing t hei ntensi tyofeachcol ourasani ntegeri nther angef rom 0t hrough255.Byso doi ngdi ff erentmi xesof256shades/ int ensi ti esofr ed,gr eenandbl uear eobt ained r esul ti ngi n256x256x256=16, 777, 216pot ent ial col our s. Soundpr oducedbyphonogr aphr ecor dsandanal ogt aper ecor der sar est oredi n anal ogf ormatasani nfi nit enumberofdi ff erentf requenci esandampl i tude.Howev er, comput ersst oressounddi git all yassequencesofnumber ssampl edat housandof t imespersecond.Pl ayi ngt hesoundi sli kest ri ngi ngt hesoundassoci atedwi tht he numbersocl oset oget hert hatt hehumanearhear sacont inui tyj ustl i kef rames pl ayedi nmot ionpi ctur e. 3 Dat aSt oragei ntheComput er Di git alcomput erst oresal lfor msofdat ae. g.i mages,sound,dat e,l ogi cal ,number , al phabet s,al phanumer icchar act ers,andmachi nei nst ruct ionsi ndi git alf orm.These di git sar eencodedi nel ement aryf orm knownasbi tst ri ng.Bi tisshor tfor mforbi nar y di gitandbi tst ri ngi sasequenceofst oredbi ts.Agr oupaf ourbi tsi scal l edani bbl e whi l ethatofei ghtbi tsi scal l edaby te.Theonl yval uesal l owedi nbi tsequencesar e 0sand1s.Thecomput ert echnol ogyenabl esi ttost oret hingsdi git ali nthr ee( 3) f orms: Elect ri cal l y,Magnet ical l yandopt ical l y. CPUandmai nmemor yar est oredel ect ri cal l y;CDsandDVDsopt ical l y,wi thl aser beamswhi l eot hersecondar yst oragesl i keHDD,Fl oppydi sket tes,andt apesar e st oredmagnet ical l y. El ect ri cal ground –v e=0, +v e=1 Opt ical dar k=0, li ght=l Magnet ic Nor thpol e=0, Sout hPol e=1 Aby te( 8bi ts)i susedt ost oreachar act erornumberi nther angef rom 0t hrough255. By tet her efor eist heuni tofmeasur ementofv olumeofdat atobest ored. Measur e Abbr evi ati onQuant it y(i nby te) By te B 20=1 Ki l oby te KB 210 =1, 024 Megaby te MB 220 =1, 048, 576 Gi gaby te GB 230 =1, 073, 741, 824 Ter aby te TB 240=1, 099, 511, 627, 776 Thecomput ermai nmemor yisar rangedi nsequenceof“ wor ds”ofdat a.Acomput er wor disabi tst ri ngandt hewor dsi zesdependsont hepar ti cul arcomput ersy stem 4 wi thonet oei ghtbei ngt hemostcommon. Numbersy stem: Thenumbersy stemsusedi ndesi gni ngcomput ersar eBi nar y,Oct al, Deci mal andHexadeci mal. Bi nar yNumber s:Bi nar ynumber sar enumber sencodedi nbase2.El ement soft his numberar e0sand1swhi chcor respondst obi tst rap. Deci mal Number s Deci malnumber sar eint egernumberwhosedi git sar esequencesof0t hrough9. Theposi ti onofeachdi githasadi ff erentwei ghti ndi cat inghow muchi tsposi ti on cont ri but est othei ntegerv alue.Her ether ightmostposi ti oni scal l ed1’ sposi ti onas i trepr esent sthenumberof1’ sint hei ntegerv alue.Thesecondposi ti onf rom t he r ighti sthe10’ sposi ti on,becauset hedi giti nthi sposi ti oncont ri but est ent imesi ts v aluet othei nteger.Thet hir dposi ti onf rom t her ighti sthe100’ sposi ti onwhi l ethe f our thposi ti oni sthe1000’ sposi ti onandsoon.Consi dert henumber5401: 5 4 0 1 1000posi ti on 100posi ti on 10posi ti on 1posi ti on 103=1000) ( 102=100) ( 101=10) ( 100=1) ( Forbi nar y,i tist hesameasabov ebut2i srepl acedwi th10i nst eade. g. 1 0 1 0 8’ sposi ti on 4’ sposi ti on 2’ sposi ti on 1’ sposi ti on 23=8) ( 22=4) ( 21=2) ( 20=1) ( 5 Compar ingbi nar ywi thot hernumbersy stems Bi nar y Deci mal Hexadeci mal 0 0 0 1 1 1 10 2 2 11 3 3 100 4 4 101 5 5 110 6 6 111 7 7 1000 8 8 1001 9 9 1010 10 A 1011 11 B 1100 12 C 1101 13 D 1110 14 E 1111 15 F Val ueofpower 20t sof2( hrough210) 20 21 22 23 24 25 26 27 28 29 210 1 2 4 8 16 32 64 128 256 312 1024 NB210=1024expl ainwhy1KB=1024by tesnot1000by tes Not eal sot hatt hemai nmemor yisdesi gnedi nmul ti plesofi ndexesof2ssuchas 256KBor512KBr athert hanot herev ennumber s. Thepowerof2i sal sousedt odet ermi net henumberofbi tsi ri ngort hegi venl engt h ofst orage.E. g.,26 =64meani ng64di ff erentbi tst ri ngst hatcanbef ormedf rom a st ri ngof6bi ts. 6 Conv ersi onofDeci mal toBi nar y:Exampl etoconv ert625t obi nar y; 1.Thel argestpowerof2i s29=512, n625i ther efor e625-512=113 2.Thel argestpowerof2i s26=64, n113i ther efor e113-64=49 3Thel argestpowerof2i s25=32, n49i ther efor e49–32=17 4Thel argestpowerof2i s24=16, n17i ther efor e17- 16=1 =1x29+0x28+0x27+1X26+1X25+1X24+0x23+0x22+0x21+1x20 =10011100012 Thesol uti oni nthepr evi oussect ionwasat echni queofconv ert ingdeci malnumber t obi nar ynumber.Anot hermet hodofconv ert ingdeci malnumbert obi nar yisby r epeat edl ysubst it uti ngt hel argestpowerof2butt hismet hodi sdi ff icul twhenl arger number sar einv olv ed.Ther eisy etanot hermet hodofconv ert ingdeci malnumbert o bi nar ywhi chi srepeat edl ydi vi ding( longdi vi sionmet hod)t henumberby2wi tht he r emai nderkepti nor der.Thequot ienti sfur therdi vi dedby2cont inuousl yunt ili t zer osoutwhi l emai ntai ningt heor deroft her emai nder.Att heend,t her emai nderi s count edf rom bot tom t othet opast her esul tedbi nar ynumber.Exampl e57i s conv ert edt obi nar yint hisway : 2 57 2 28R1 2 14R0 2 7R0 2 3R1 2 1R1 0R1 Count ingf rom bot tom t othet opoft her emai nder s:111001t obase2. Conv ert ingf ract ional par tofanumbersy stem: Thesamewaydeci malnumber susedeci malpoi ntt odemar cat efr act ion,t hesame 7 occur sinbi nar ywi tht heat tendantmi nussi gni g.3-x=1/ ndexe. 3xso2-1=½ 102 =22x1+21x0+20x1+2-1x1+2-2x0 ( 101. ½+0) 4+0+1+1/ 2=5. 50 11012=1x2-1+1x2-2+0x2-3+1x2-4 0. =½ +¼+0+1/ 16 =13/ 16 =0. 8125 101. 10 3’ sposi ti on 2’ sposi ti on 1’ sposi ti on ½’ sposi ti on ¼’ sposi ti on Toconv ertt hef ract ionpar tofdeci mal numbert obi nar y,cont inuousmul ti pli cat ioni s per for medbutr etai ningal lther esul ti ngi ntegerbi ts.Att heend,t hei ntegerbi tsar e or der edf rom t hegr eat estwei ghtt othel east. Comput erCommuni cat ions Comput ershav etheabi l ityt ocommuni cat ewi theachot herbyconnect ingt hem t oget herusi ngat echnol ogyknownasnet wor k.Net wor kwi thi nof fi ce/ schoolar eai s cal l edLAN ( localar eanet wor k)whi l etheonewi thawi dergeogr aphi calar eai s cal l edWAN( widear eanet wor k). Bot hLANandWANi ntoday ’snet wor kar econnect edt othei nter net.Int ernetmeans i nter nat ionalnet wor kconsi sti ng ofa col l ect ion ofdi ff erentnet wor kconnect ed t oget herbutar rangedi nadecent ral i zedmanner. Bef oret hei nter net ,tel ephoneorv oicel i nesusesdev icecal l edmodem t oenabl e comput erhandl ecommuni cat ion.Ear li ermoder nhav ebet weenwi dthorconnect ing capaci tyof56Kbpersec,now i nter netser vicepr ovi der s(I SPs)pr ovi dephy sical connect ionst othei nter netf orcust omer swhoneedt heseser vices. Comput ersconnect edt oal lki ndsofnet wor k(LAN, WAN, Int ernet )adher etor ulesof communi cat ionst andar dknownaspr otocol. 8 Communi cat ionspeedt hroughanymedi um i smeasur edi nki l obi tspersecond, Kb/ sec.Ot herdev icesl i kecabl emodemst ransmi tsat1. 5Mbps( megabi tpersec). Dat ali neswi thi tsaddi ti onalbandwi dthof10Mbpsi spr efer redi nLANs.Et her net t echnol ogyt ransmi tsat12. 8Gbpsi nATM ( Asy nchr onoust ransf ermode). PC LAN PC I nter net Tel ephone PC I SP PC I SP PC I SPsuseTxl i nest ocommuni cat e,mostcommonl yusedar eT1l i nes( 1.5Mbps)or T3l i nes( 45Mbps) Component sofNet wor ks:Net wor ksar emadeupofCl i entcomput ers,Net wor k connect ingdev icesandSer ver s. Cl i entcomput ers–comput eri nhomeandof fi ces Net wor kconnect ingdev ices–swi tches, rout ers, hubs, bri dges, modems, mul ti plexer , NI C(net wor kint erf acecar d), adapt erset c.. Ser ver–pr ovi desser vices, webser vices, Dat abaseser vices, Net wor kser viceset c. I NTERNETBASI CS The i nter net i sat oolf or per sonalconv ersat ion,r esear ch,commer ce and ent ert ainment.Thei nter neti soneoft hemosti mpor tantf act orsshapi ngourl i feand t hef utur e.I thaschangedt hewaymanypeopl ewor k,communi cat eanddobusi ness. I thasenabl edusaccessnear lyanyki ndofi nfor mat ionf rom aPC,t husgi vi ngus newwayt oshop, study ,wor k,andsoci ali ze. 9 Howi twor ks Hast hepot ent ialt oli nky ourcomput ert oanyot hercomput eri nthewor ld.I nter net wor kswi tht hehel pofapr otocolknownasTCP/ IP.Thi spr otocolal socal l edt he Uni ver sal languageoft hei nter netper for mthef oll owi ngf unct ions: 1.Tr ansmi ssi oncont rolpr otocol /I nter netpr otocolsett her ulesandpr ocedur es t hatcont rol sthewaydat aisf ormat ted, andt ransmi tt edamongstcomput ers. 2.I tconsi stofspeci fi cat ionst hati dent if iesi ndi vi dualcomput erst hatenabl e t hem t oexchangedat a.I ncl udesr ulest orundi ff erentki ndsofappl i cat ioni n di ff erentcomput erswi thot heroper ati ngsy stem. Rout ingacr osst heI nter net Thecor eoft hei nter neti sasetofbackboneconnect ionst hatt iet hel ocaland r egi onalnet wor kst oget herandt her out ingschemecont rol sthewayeachpi eceof dat afi nds i ts dest inat ion.Smal l ernet wor ks connectt othe I nter netbackbone t hroughgat eway s.ALANwi thoutTCP/ IPr equi resr out erandgat ewayt oconnectt o t hei nter net. Addr essi ngSchemes Ev erycomput erhasaf our -par tnumer icaddr esscal l edI nter netpr otocoladdr essor ( IPaddr ess)t hatcont ainsr out ingi nfor mat iont hati dent if iesi tsl ocat ions.Eachpar t oft hef ourquar tetnumberr angesbet ween0and255e. g.205. 46. 117. 104.Most comput ers on t he i nter netal so hav e an addr ess cal l ed domai n name sy stem addr essDNS–anaddr esst hatuseswor dsr athert hannumber s. DNShast wopar ts:hostnameanddomai nnamet hatgener all yident if iest het ypeof i nst it uti ont hatusest headdr ess.Bel ow ar esomedomai nnamesav ail abl eont he i nter net : 10 Tabl e1:Top- lev elDomai nnamesi ntheI nter net Domai n Ty peofOr gani zat ion Exampl e. com Busi ness( commer cial ) i bm. com, googl e.com. edu Educat ional pamo. edu. gov Gov ernment whi tehouse. gov. mil Mi l itar y nav y.mi l. net Gat ewayorhost mi ndspr ing. net ( busi ness/ commer cial ( ISP). org Ot her or gani zat ion i soc. org ( nonpr ofi t) Tabl e2: NewTop- lev elDomai ns Domai n Ty peofor gani zat ion. inf o I nfor mat ional websi te. biz Busi nessr elat edsi te. name Domai nregi str ati onf ori ndi vi dual s Tabl e3: OtherTop- lev eldomai nunderconsi der ati on Domai n Ty peofor gani zat ion. aer o Ai rtr anspor tindust ry. coop Cooper ati ves. museum Museums. pro Account ant ,lawy ers, phy sici ans 11 Wor ldWi deWeb( WWW) Webi sat ypeofser viceav ail abl etoper sonswhocanuset hei nter net.WWW was cr eat edatt heEur opeanPar ti clePhy sicsLabor ator y(EPPL)i nGenev ain1989,a met hod f ori ncor por ati ng f oot not es,f igur es and cr oss- ref erences i nto onl i ne hy per textdocument s,usi ngapr otocolknownast hehy per textt ransf erpr otocol ( HTTP).Ahy per textdocumenti saspeci all yencodedf il ethatusest hehy per text mar kup l anguage ( HTML).Thi slanguage al l owsa documentaut hort o embed hy per textl i nks( alway s-cal l edhy per li nks)i nthedocument.Acol l ect ionofr elat ed webpagesar ecal l edwebsi te.Webser ver shouseWebsi tes.Copy ingapageont oa webser veri scal l edPOSTI NGt hepage.I nter act ivewebpagesper mit sreader sto consul tdat abases,or derpr oduct s,andi nfor mat ion,andsubmi tpay mentwi tha cr edi tcar d orot heraccountnumber.Web br owseri s a sof twar e appl i cat ion desi gnedt ofi ndhy per textdocument sont hewebandt henopent hedocument son t heuser ’scomput er. Twot ypesofBr owser s 1.Point- and-cl i ckbr owserusesGUI( Graphi csUserI nter face)e. g.Net scape, explor er,Opera, Chromeetc. 2.Textbasedwi thbr owserusesnon- GUIe. g.ol dUni x HTTPandURLs HTTPusesi nter netaddr essesi naspeci alf ormat ,cal l edauni for mresour cel ocat or ( URL).WWW i sbui l tonasetr ulescal l edhy per textt ransf erpr otocol( HTTP).HTTP andhy per textl i nksar ethef oundat ionoft hewww. Thef ormatofURL t ype: //addr ess/ pat h/ - t ypespeci fi est het ypeofser veri nwhi cht hef il elocat ed - addr essi ntheaddr essoft heser veand - pat hist hel ocat ionwi thi nthef il est ruct ureoft heser ver.Incl udesl i stof f older s/di rect ori eswher ethedesi redf il eisl ocat ed. 12 WebPor tal s Thesear efr eeper sonal i zedst art -uphomepagehost edbyawebcont entpr ovi der t haty oucanper sonal i zei nsev eral way s.Websi teswi thpor tal ser vicesar e: a)Mi crosof tnet wor k(MSN)ht tp: //www. msn. com/ b)Net scapeNet cent re.ht tp: //www. net scape. com/ c)Exci te–ht tp: //www. exci te. com/ d)Yahooht tp/ /www. yahoo. com/ e)Googl eht tp: //www. googl e.com/ Awebpor tal hast woadv ant agesov erat ypi cal per sonal homepage 1)Ri ch,dy nami ccont ent :di ff erentt ypesofi nfor mat ionandgr aphi cse. g.news, spor ts,weat her ,ent ert ainmentnews,f inanci ali nfor mat ion,mul ti ple sear ch engi nes,chatr oomsaccess,e- mai let c.Cont entofpor talar eupdat edf requent ly aut omat ical l y. 2)Cust omi zat ion:Thi smeanssel ect ingt het ypeofi nfor mat iony ouwantt ovi ew. Thi smayi ncl udehy per li nksenabl i ngy ougot oot hersi tes. Tosetupapor talv isi tanyoft heabov esi tesbookf oral i nksuchas‘ per sonal i ze my …’ormaket hisy ourhomepage.Cl i ckandseet heopt ionswi l lappearf ory our bestpi ck.Not e: 1.Themor eopt iony ouchoose, mor eti met hebr owsert akest oload. 2.Whent heopt ionsar esav ed,t hepor talgener atest hesav eopt ionsascooki e.A cooki eisasmal lfi l ethatcont ainsset ti ngi nfor mat ion.I fthecooki eisdel etedt he set ti ngi nfor mat iongoes.Cooki esar enothar mfult oyoursy stem t houghsome websi tesusecooki est oret ri eveper sonali nfor mat ionf rom t hecomput erand t racky ourbr owsi ngact ivi ti es. 13 El ect roni cmai l(e- mai l ) Theactofcr eat ing, sendi ngandr ecei vi ngmai lthr ought hei nter net.Todot hiseach usermusthav ee- mai laddr ess.Thi sisauni queusernameaddr esssetupf rom DNS addr essesandnumer icI Paddr essesav ail abl e.Thef ormati stheusernamef ir st, separ ated f rom t he DNS addr ess by an “ at” sy mbol , ( @). e. g. whosename@gmai l.com Whenemai lissent ,themessagei sst oredonemai lser verunt ilt her eci pientcan r etr iev eit.Mostmai lser ver suset hepostof fi cepr otocol( POP).Nowwebsi tesl i ke hot mai l ,mai l.com, yahoo, Googl eandot her spr ovi def reee- mai laccount s. St ayi ngCi vi lOnl i ne Thi s concer ns appr opr iat e behav ioron t he i nter netcal l ed net iquet te( int ernet et iquet te)t hought her eisnowr it tenr ulegov erni ngbehav ioront hei nter net. 1.Behav eoractasi fyouar ecommuni cat ingt otheper sonf acet oface. 2.Post sar eopen t oint erpr etat ion.Becar efulnott o useof fensi vewor dsor r emar ks. 3.Do not‘ shout ’onl i ne:t ypi ng i n al lcapi tall ett ersi sli ke shout ing and i tis consi der edr ude. 4.Donotf lameot heruser s:I n‘netspeak’ afl amei sapost ingt hatcont ainsi nsul ts order ogat orycont ent.Fl amer sar eusual l yshutoutorbl ockedbyot heruser s, 5.Do notsend spam:Spam i stheonl i neequi val entofj unkmai l– uni nvi ted messages, usual l yofacommer cial nat ure. 6.Do notr edi str ibut e copy right ed mat eri als:These ar e pages orpost s wi th copy right ed and t rademar ked t extand gr aphi cspost ed wi thoutt he owner ’s per missi on.Foundmost lyi nUsenetnewsgr oup.Becausey ouf indt hem ont he i nter netdoesnotmeant hatcopy rightl awdoesnotappl y. 7.Donotbeacowar donl i ne:Asagener alr ulenev erconcealy ouri dent it yont he i nter net.Ify ouchooseascr eenname, donothi debehi ndi ttomi sbehav e.Fi nal l y, al way scheckr uleswheny ougoonl i ne. 14 Wor kingont heI nt