types of internal storage.doc

7/27/2019 TYPES OF INTERNAL STORAGE.doc

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TYPES OF INTERNAL STORAGE

The internal storage section is the holding area in which instructions and data are kept For thecontrol section to control and coordinate all processing acti!it"# it $ust %e a%le to locate eachinstruction and data ite$ in storage A particular progra$ instruction or data ite$ that is held instorage can %e located %" knowing its address Each co$puter word contains a group o&

characters at a single address So$e o& the $ore co$$on t"pes o& internal storage $edia usedin toda"'s co$puters are as &ollows( $agnetic core# se$iconductor# and %u%%le

)AGNETI* *ORE STORAGE

)agnetic core storage is $ade up o& tin" doughnut+shaped rings $ade o& &errite ,iron-# that arestrung on a grid o& !er" thin wires Since data in co$puters is stored in %inar" &or$ or a two+statede!ice is needed to represent the two %inar" digits ,%its-# . &or o&& and / &or on In core storage#each &errite ring can represent a . or / %it# depending on its $agnetic state I& $agneti0ed in onedirection# it represents a / %it# and i& $agneti0ed in the opposite direction# it represents a . %itThese cores are $agneti0ed %" sending an electric current through the wires on which the core isstrung It is this direction o& current that deter$ines the state o& each core

SE)I*ON12*TOR STORAGE ,T3E SILI*ON *3IP-

Semiconductor memory consists o& hundreds o& thousands o& tin" electronic circuits etched ona silicon chi Each o& these electronic circuits is called a bit cell and can %e in either an o&& or onstate to represent a . or / %it# depending on whether or not current is &lowing in that cell In otherword# se$iconductor $e$or" chips is integrated circuits (ICs) 1e!elop$ents in technolog"ha!e led to large scale integration ,LSI-# which $eans that $ore and $ore circuits can %es4uee0ed onto the sa$e silicon chip *o$panies are e!en $anu&acturing very large scale

integrated circuits ,5LSI-# which $eans e!en &urther $iniaturi0ation

Figure 6+7 + A se$iconductor $e$or" chip ,integrated circuit-



So$e o& the ad!antages o& se$iconductor storage are &ast internal processing speeds# highrelia%ilit"# low power consu$ption# high densit" ,$an" circuits-# and low cost 3owe!er# there is adraw%ack to this t"pe o& storage It is volatile# which $eans all data in $e$or" is lost when thepower suppl" is re$o!ed Should the power on "our co$puter &ail and "ou ha!e no %ackup powersuppl"# all the stored data is lost This is not the case with $agnetic core storage *ore storage isnon!olatile This $eans the data is retained e!en i& there is a power &ailure or %reakdown# sincethe cores store data in the &or$ o& magnetic charges rather than electric current

8288LE STORAGE

One o& the latest technological de!elop$ents in storage $edia is the introduction o& %u%%le$e$or" Bubble memory consists o& a !er" thin cr"stal $ade o& se$iconductor $aterial The$olecules o& this special cr"stal act as tin" $agnets ,&ig 6+9- The polarit" o& these $olecules or

:$agnetic do$ains: can %e switched in an opposite direction %" passing a current through acontrol circuit i$printed on top o& the cr"stal In this $anner# data can %e stored %" changing thepolarit" o& the $agnetic do$ains Since the principle is the sa$e as &or $agnetic core storage#%u%%le $e$or" is considered non!olatile The data is retained e!en i& there is a power &ailureFurther$ore# the process o& reading &ro$ %u%%le $e$or" is nondestructive# $eaning that thedata is still present a&ter %eing read This is not the case with core storage# which $ust %eregenerated a&ter %eing read I& we were to !iew these $agnetic do$ains under a $icroscope#the" would look like tin" %u%%les; hence the na$e# %u%%le $e$or"

Figure 6+9 + 8u%%le $e$or"

<= )agnetic core storage is $ade up o& what></. A se$iconductor $e$or" consists o& what>



<// ?hat is another na$e &or se$iconductor $e$or" chips></6 In co$puter storage# what does !olatile $ean></@ ?hat t"pe o& storage can retain its data e!en i& there is a power &ailure or %reakdown></7 8u%%le $e$or" consists o& what></9 3ow are the $agnetic do$ains o& a %u%%le $e$or" switched></ ?hat do we $ean when we sa" that reading &ro$ %u%%le $e$or" is nondestructi!e>

*LASSIFI*ATIONS OF INTERNAL STORAGE

2p to this point# "ou ha!e learned so$e o& the general &unctions o& the cpu# the ph"sicalcharacteristics o& $e$or"# and how data is stored in the internal storage section Now# we willeBplain "et another wa" to classi&" internal ,pri$ar" or $ain- storage This is %" the di&&erent kindso& $e$ories used within the cpu( read+onl" $e$or"# rando$+access $e$or"# progra$$a%leread+onl" $e$or"# and erasa%le progra$$a%le read+onl" $e$or"

REA1+ONLY )E)ORY ,RO)-

In $ost co$puters# it is use&ul to ha!e o&ten used instructions# such as those used to %ootstrap,initial s"ste$ load- the co$puter or other speciali0ed progra$s# permanently stored inside the

co$puter )e$or" that ena%les us to do this without the progra$s and data %eing lost ,e!enwhen the co$puter is powered down- is called read+onl" $e$or" Onl" the co$puter$anu&acturer can pro!ide these progra$s in RO) and once done# the" cannot %e changed*onse4uentl"# "ou cannot put an" o& "our own data or progra$s in RO) )an" co$pleB&unctions such as routines to eBtract s4uare roots# translators &or progra$$ing languages# andoperating s"ste$s can %e placed in RO) $e$or" Since these instructions are hard wired,per$anent-# the" can %e per&or$ed 4uickl" and accuratel" Another ad!antage o& RO) is that"our co$puter &acilit" can order progra$s tailored &or its needs and ha!e the$ per$anentl"installed in RO) %" the $anu&acturer Such progra$s are called $icroprogra$s or firmware

RAN1O)+A**ESS )E)ORY ,RA)-

Another kind o& $e$or" used inside co$puters is called rando$+access $e$or" ,RA)- or

readCwrite $e$or" RA) $e$or" is rather like a %lack%oard on which "ou can scri%%le downnotes# read the$# and ru% the$ out when "ou are &inished with the$ In the co$puter# RA) is theworking $e$or" 1ata can %e read ,retrie!ed- &ro$ or written ,stored- into RA) Dust %" gi!ing theco$puter the address o& the location where the data is stored or is to %e stored ?hen the data isno longer needed# "ou can si$pl" write o!er it This allows "ou to use the storage again &orso$ething else *ore# se$iconductor# and %u%%le storage all ha!e rando$ access capa%ilities

PROGRA))A8LE REA1+ONLY )E)ORY ,PRO)-

An alternati!e to RO) is progra$$a%le read onl" $e$or" ,PRO)- that can %e purchasedalread" progra$$ed %" the $anu&acturer or in a %lank state 8" using a %lank PRO)# "ou canenter an" progra$ into the $e$or" 3owe!er# once the PRO) has %een written into# it can ne!er%e altered or changed Thus "ou ha!e the ad!antage o& RO) with the additional &leBi%ilit" toprogra$ the $e$or" to $eet a uni4ue need The $ain disad!antage o& PRO) is that i& a $istakeis $ade and entered into PRO)# it cannot %e corrected or erased Also# a special de!ice isneeded to :%urn: the progra$ into PRO)

ERASA8LE PROGRA))A8LE REA1+ONLY )E)ORY ,EPRO)-

The erasa%le progra$$a%le read+onl" $e$or" ,EPRO)- was de!eloped to o!erco$e thedraw%ack o& PRO) EPRO)s can also %e purchased %lank &ro$ the $anu&acturer andprogra$$ed locall" at "our co$$andCacti!it" Again# this re4uires special e4uip$ent The %ig



di&&erence with EPRO) is that it can %e erased i& and when the need arises 1ata and progra$scan %e retrie!ed o!er and o!er again without destro"ing the contents o& the EPRO) The" willsta" there 4uite sa&el" until "ou want to reprogra$ it %" &irst erasing the EPRO) with a %urst o&ultra+!iolet light This is to "our ad!antage# %ecause i& a $istake is $ade while progra$$ing theEPRO)# it is not considered &atal The EPRO) can %e erased and corrected Also# it allows "outhe &leBi%ilit" to change progra$s to include i$pro!e$ents or $odi&ications in the &uture

</ In what t"pe o& $e$or" are o&ten used instructions and progra$s per$anentl" stored inside

the co$puter>

</ ?ho pro!ides the progra$s stored in RO)>

</= *an progra$s in RO) %e changed>

<6. ?hat is another na$e &or rando$+access $e$or" ,RA)->

<6/ 3ow is data read &ro$ or written into RA)>

<66 In what two states can progra$$a%le read+onl" $e$or" ,PRO)- %e purchased>

<6@ ?hat is the $ain disad!antage o& PRO)>

<67 ?hat does EPRO) stand &or>

<69 3ow is EPRO) erased>

SE*ON1ARY STORAGE

The last kind o& $e$or" we will %rie&l" introduce here is called secondary storage or auxiliarystorage This is $e$or" outside the $ain %od" o& the co$puter ,cpu- where we store progra$sand data &or &uture use ?hen the co$puter is read" to use these progra$s and data# the" areread into internal storage Secondar" ,auBiliar"- storage $edia eBtends the storage capa%ilities o&the co$puter s"ste$ ?e need it &or two reasons First# %ecause the co$puter's internal storageis li$ited in si0e# it cannot alwa"s hold all the data we need Second# in secondar" storage# dataand progra$s do not disappear when power is turned o&& Secondar" storage is non!olatile This$eans in&or$ation is lost onl" i& "ou# the user# intentionall" erase it The three t"pes o& secondar"

storage we $ost co$$onl" use are $agnetic disk# tape# and dru$

)AGNETI* 1IS

The popularit" o& disk storage de!ices is largel" %ecause o& their direct-access capa%ilities )oste!er" s"ste$ ,$icro# $ini# and $ain&ra$e- will ha!e disk capa%ilit" )agnetic disks rese$%lephonograph records ,round platters-# coated with a $agneti0a%le recording $aterial ,iron oBide-#%ut their si$ilarities end there )agnetic disks co$e in $an" di&&erent si0es and storagecapacities The" range &ro$ @ inches to 7 &eet in dia$eter and can store &ro$ 69 $illion to ..$illion characters ,%"tes- o& data

The" can %e porta%le in that the" are re$o!a%le# or the" can %e per$anentl" $ounted in thestorage de!ices called disk dri!e units or disk dri!es The" can %e $ade o& rigid $etal ,harddisks- or &leBi%le plastic ,&lopp" disks or diskettes- as shown in &igure 6+

Figure 6+ + 5arious t"pes and si0es o& $agnetic disk storage

http://www.tpub.com/neets/book22/92i.htm












)usic is stored on a phonograph record in a continuous groo!e that spirals into the center o& therecord 8ut there are no groo!es on a $agnetic disk Instead# data is stored on all disks in anu$%er o& in!isi%le concentric circles called tracks Each track has a designated nu$%er%eginning with track ... at the outer edge o& the disk The nu$%ering continues se4uentiall"toward the center to track /==# ..# or whate!er the highest track nu$%er is No track e!ertouches another ,&ig 6+- The nu$%er o& tracks can !ar" &ro$ @9 to on a &lopp" disk sur&aceand &ro$ 6.. to o!er .. on hard disk sur&aces

Figure 6+ + Location o& tracks on the disk's recording sur&ace



1ata is written as tin" $agnetic %its ,or spots- on the disk sur&ace Eight+%it codes are generall"used to represent data Each code represents a di&&erent nu$%er# letter# or special character Inchapter 7# "ou'll learn how the codes are &or$ed ?hen data is read &ro$ the disk# the data on thedisk re$ains unchanged ?hen data is written on the disk# it replaces an" data pre!iousl" storedon the sa$e area o& the disk

*haracters are stored on a single track as strings o& $agneti0ed %its ,.'s and /'s- as shown in&igure 6+ The / %its indicate $agneti0ed spots or ON %its The . %its represent un$agneti0edportions o& the track or OFF %its Although the tracks get s$aller as the" get closer to the centero& the disk platter# each track can hold the sa$e a$ount o& data %ecause the data density isgreater on tracks near the center

Figure 6+ + A string o& %its written to disk on a single track



A track can hold one or $ore records A record is a set o& related data treated as a unit Therecords on a track are separated %" gaps in which no data is recorded# and each o& the records ispreceded %" a disk address This address indicates the uni4ue position o& the record on thetrack and is used to directl" access the record Figure 6+= shows a track on which &i!e recordsha!e %een recorded 8ecause o& the gaps and addresses# the a$ount o& data we can store on atrack is reduced as the nu$%er o& records per track is increased Records on disk can %e %locked,grouped together- Onl" one disk address is needed per %lock# and as a result# &ewer gapsoccur ?e can use the %locking techni4ue to increase the a$ount o& data we can store on onetrack

Figure 6+= + 1ata records as the" are written to disk on a single track

Link Bar 0

The storage capacit" o& a disk depends on the bits per inch of track and the tracks per inch ofsurface 2sing ?inchester technolog"# the designers o& disk dri!e units were a%le to increase thedata densit" o& a disk %" increasing the nu$%er o& tracks ?inchester was the code na$e used%" I8) during the de!elop$ent o& this technolog" The designers originall" planned to use dualdisk dri!es to introduce the new concept Each dri!e was to ha!e a storage capacit" o& @. $illioncharacters# and thus was eBpected to %e a :@.+@.: Since that was the cali%er o& a &a$ous ri&le#

the new product was nickna$ed :?inchester: The designers &ound that data densit" could %ei$pro!ed and storage capacit" increased %" reducing the &l"ing height# the distance o& thereadCwrite heads o!er the disk sur&aces when reading and writing 8" doing this# s$aller$agneti0ed spots could %e precisel" written and then read The readCwrite heads were $o!ed soclose to the disk that a hu$an hair looked like a $ountain in the path o& the &l"ing head?inchester technolog" reduces this potential pro%le$ %" sealing the disks in a conta$ination+&reecontainer This eli$inates &oreign o%Dects &ro$ co$ing in contact with the readCwrite heads



1ata can %e ph"sicall" organi0ed in one o& two wa"s on a disk pack# depending on the$anu&acturer and the $odel o& disk dri!e "ou are using One wa" uses the c"linder $ethod# andthe other uses the sector $ethod On diskettes# data is organi0ed using the sector $ethod

The cylinder method uses a c"linder as the %asic re&erence point ?hen "ou look at &igure 6+/.#!iew A# "ou will see a disk pack containing siB disk platters with /. recording sur&aces I$agine

"ou are looking down through the disk pack &ro$ the top All the tracks with the sa$e nu$%er lineup !erticall" Together the" are called a c"linder These /. tracks# one on each recording sur&ace#can %e re&erenced %" the /. readCwrite heads on the &i!e access ar$s at each discrete locationwhere the access ar$s can %e positioned

Figure 6+/.A + Ph"sical organi0ation o& data on a disk *YLIN1ER )ET3O1

There&ore# to ph"sicall" re&erence a record stored using the c"linder $ethod# a computerprogram $ust speci&" the cylinder number # the recording surface number # and the recordnumber as shown in &igure 6+/.# !iew A 3ere# the record is stored in c"linder 69 o& recordingsur&ace and is the &irst record on that track Special data stored on each track speci&ies the%eginning o& the track so that the &irst record# second record# third record# and so on# can %eidenti&ied

Another wa" to ph"sicall" organi0e data on the disk pack ,and on diskettes- is to use the sectormethod This re4uires that each o& the tracks %e di!ided into indi!idual storage areas calledsectors ,shown in &igure 6+/.# !iew 8- The nu$%er o& sectors !aries with the disk s"ste$ used;howe!er# there are usuall" eight or $ore Each sector holds a speci&ic nu$%er o& characters8e&ore a record can %e accessed# a computer program $ust again gi!e the disk dri!e therecord's address speci&"ing the track number # the surface number # and the sector number o&the record One or $ore readCwrite heads are then $o!ed to the proper track# the head o!er thespeci&ied sur&ace is acti!ated# and the data is read &ro$ or written to the designated sector as itspins under the head



Figure 6+/.8 + Ph"sical organi0ation o& data on a disk SE*TOR )ET3O1

)AGNETI* TAPE

Another t"pe o& storage de!ice is $agnetic tape which is si$ilar to the tape used with co$$ercialtape recorders It is used $ainl" &or secondar" storage It di&&ers &ro$ co$$ercial tape in that it isusuall" wider ,ranging &ro$ one+hal& inch to an inch-# and it is $anu&actured to $ore rigid 4ualit"

speci&ications It is $ade o& a )YLAR %ase coated with a $agnetic oBide that can %e $agneti0edto store data )agnetic tape co$es in a !ariet" o& lengths ,&ro$ .. to @#... &eet-# and ispackaged in one o& three wa"s( open reel# cartridge# or cassette# as shown in &igure 6+// Largeco$puters use standard open reels# /C6+inch wide tape# 6#7.. &eet in length )agnetic tape unitsare categori0ed %" the t"pe o& packaging used &or the tape The tape unit ,or dri!e- shown in&igure 6+/6 uses open reels# while cartridge tape units use tape cartridges and cassette units usetape cassettes *artridge tape units are o&ten used on personal co$puters to pro!ide %ackup &orhard disk

Figure 6+// + 5arious t"pes o& $agnetic tape storage



Figure 6+/6 + )ounting a $agnetic tape



A standard /C6+inch tape $a" ha!e either se!en ,&ig 6+/@# !iew A- or nine tracks ,&ig 6+/@ # !iew8- o& data stored on it# depending upon the particular readCwrite heads installed in the tape unitReadCwrite heads are usuall" designed to read ,or write- data ,in the &or$ o& %its- concurrentl"across the width o& the tape

Figure 6+/@ + )ulti+track $agnetic tape



The a$ount o& data or the nu$%er o& binary digits ,. and / %itsthat can %e written ,storedon alinear inch o& tape is known as the tape's recording density *o$$on recording densities &or$ultitrack tapes range &ro$ 6.. to #69. %itsC%"tes per inch ,8PI- Also note that so$eti$es thedensit" o& a tape is re&erred to as the nu$%er o& &ra$es per inch ,FPI- or characters per inch,*PI- rather than 8PI Regardless o& which ter$ is used# a &ra$e or %"te is a group o& related %itsthat $ake up a single character written across the width o& the tape )ost $agnetic tape units arecapa%le o& reading and writing in se!eral di&&erent densities

)agnetic tapes ha!e $an" co$$on &eatures and data recording &or$ats Each tape is ph"sicall"$arked in so$e $anner to indicate where reading and writing on tape is to %egin ,known as thebeginning-of-tape !B"#$-# and where it ends ,known as the end-of-tape !%"#$- The length o&tape %etween the 8OT and EOT is re&erred to as the usable recording (reading&writing)surface or usa%le storage area 8OTCEOT $arkers are usuall" $ade o& short sil!er strips o&re&lecti!e tape ,/C7+inch wide %" /C6+inch long- as shown in &igure 6+/7 The 8OT $arker isnor$all" placed toward the &ront edge o& the tape ,the side nearest "ou when the tape is $ountedon the tape unit- The EOT $arker is placed toward the %ack edge ,the side &arthest &ro$ "ouwhen the tape is $ounted on the tape unit- The" are placed approBi$atel" /9 to 6. &eet in &ro$each end on the shin" side o& the tape So$eti$es# holes or clear plastic inserts are used as$arkers in place o& re&lecti!e strips Regardless o& the $ethod used# the 8OTCEOT $arkers aresensed %" an arrange$ent o& la$ps andCor photodiode sensors to indicate where reading andwriting is to %egin and end

Figure 6+/7 + 8eginning+o&+tape ,8OT- and end+o&+tape ,EOT- $arkers

?e can $ake records on $agnetic tape an" si0e we need to hold the data ?e are restricted onl"%" the length o& the tape or the capacity o& internal storage For eBa$ple# a record can %e onecharacter# se!eral characters# or thousands o& characters in length The collection o& records iscalled a &ile A &ile containing pa"roll records is called a pa"roll &ile; a &ile containing suppl"in!entor" records is called a suppl" in!entor" &ile

Records can %e placed on tape either separatel" as single records ,un%locked- as shown in &igure6+/9# !iew A# or $ultiple records can %e grouped together ,%locked- as shown in &igure 6+/9# !iew8# to &or$ a record block The nu$%er o& records stored in a record %lock is the blocking factor

In this eBa$ple# the %locking &actor is &i!e

Figure 6+/9 + Record &or$ats on $agnetic tape



All $agnetic tape $ust %e $o!ing at a predeter$ined speed &or data to %e read &ro$ or written onthe tape 1ata cannot %e read or written while the tape is co$ing up to speed# slowing down# orstopped 1uring this ti$e dela"# the tape $o!es a short distance creating a blank spot on thetape This interrecord gap or interblock gap separates each single record or %lock o& recordson the tape The length o& the gap !aries# depending upon the particular s"ste$ and $ethod o&recording# %ut is approBi$atel" 6C9 to @C7 inch in length I& single records are stored on the tape#the interrecord gap $a" %e longer than the portion o& tape used to store the record There&ore#$uch o& the tape's recording sur&ace is wasted

To o!erco$e the ine&&icienc" o& storing single data records# we nor$all" %lock records In &igure6+/9# !iew 8# "ou will notice the tape is used $ore e&&icientl" than the tape in &igure 6+/9# !iew A8locking allows $ore data to %e stored on a reel o& tape

1uring reading# the record %egins with the &irst character sensed &ollowing an interrecord orinter%lock gap and continues until the neBt gap is reached All input records read are internall"stored in accordance with the a$ount o& storage area set aside %" the applications progra$

)agnetic tape# as a storage $edia# o&&ers se!eral use&ul &eatures ?e can store large a$ounts o&data in a !ariet" o& con!enient package si0es ,open reels# cartridges# or cassettes- )agnetictapes are easil" interchangea%le %etween si$ilar tape units o& di&&erent co$puter s"ste$s# andtapes are less prone to da$age than other t"pes o& storage $edia

)AGNETI* 1R2)

Like the $agnetic disk# the $agnetic dru$ is another eBa$ple o& a direct-access storage de!ice

Although the $agnetic dru$ was once used as $ain ,or pri$ar"- storage# it is now used assecondar" ,or auBiliar"- storage 2nlike so$e disk packs# the $agnetic dru$ cannot %e ph"sicall"re$o!ed The dru$ is per$anentl" $ounted in the de!ice

)agnetic dru$ storage de!ices consist o& either a hollow c"linder ,thus# the na$e dru$- or asolid c"linder that rotates at a constant !elocit" ,&ro$ .. to #... rp$- The outer sur&ace iscoated with an iron+oBide $aterial capa%le o& %eing $agneti0ed



A $agnetic dru$ di&&ers &ro$ a $agnetic disk in that the tracks in which the data is stored areassigned to channels located around the circu$&erence o& the dru$ as shown in &igure 6+/ Thatis# the channels &or$ circular %ands around the dru$ The coded representation o& data in &igure6+/ is si$ilar to that used on =+track $agnetic tape# +%it code The %asic &unctions o& thereadCwrite heads are to place $agneti0ed spots ,those little %inar" .'s and /'s- on the dru$ duringa writing operation and to sense these spots during a reading operation The readCwrite heads o&a dru$ per&or$ in a $anner si$ilar to the readCwrite heads o& a $agnetic tape unit or disk dri!eunit

Figure 6+/ + )agnetic dru$

The tracks on each channel are grouped into sectors as illustrated in &igure 6+/ 1oes thissound &a$iliar to "ou> It sounds al$ost like the &or$at used on disk packs when re&erring totracks ,or c"linders- and sectors As the dru$ rotates# the reading or writing occurs when thespeci&ied sector o& a gi!en channel passes under the readCwrite head &or that channel

So$e dru$s are $ounted in a hori'ontal position# such as the one shown in &igure 6+/# whileothers are $ounted in a vertical position Another $aDor di&&erence in the design is the nu$%er o&readCwrite heads So$e dru$s use onl" one readCwrite head# which ser!ices all channels on the

dru$ In this case# the head $o!es %ack and &orth ,or up and down- o!er the sur&ace o& the dru$as re4uired Other dru$s# using $ultiple readCwrite heads# ha!e one principal ad!antage o!erdru$s with the single+head t"pe Since one readCwrite head is assigned to each channel# noreadCwrite head $o!e$ent is re4uired That is# the ti$e re4uired &or head positioning is 0ero Theonl" signi&icant ti$e re4uired when reading or writing is the rotational delay that occurs inreaching a desired record location

To gi!e "ou so$e idea o& speed and storage capacities# so$e high+speed dru$s are capa%le o&trans&erring o!er one $illion characters o& data per second# which is roughl" e4ui!alent to reading



a stack o& punched cards &eet high in one second The storage capacities o& $agnetic dru$srange &ro$ 6. $illion to $ore than /9.#... $illion characters ,or %"tes- o& data

<6 ?h" are disk storage de!ices popular>

<6 3ow is data stored on all disks>

<6 ?hat precedes each record on a disk>

<6= 3ow is the storage capacit" o& a disk deter$ined>

<@. ?hat two wa"s can data %e ph"sicall" organi0ed on a disk pack><@/ The a$ount o& data that can %e stored on a linear inch o& tape is known %" what ter$>

<@6 The length o& tape %etween 8OT and EOT is re&erred to %" what ter$>

<@@ 3ow does a $agnetic dru$ di&&er &ro$ a $agnetic disk>

<@7 Tracks on each channel o& a $agnetic dru$ are grouped into what>

Link Bar 1

INP2TCO2TP2T 1E5I*ES ,EHTERNAL-

Input and output de!ices are si$ilar in operation %ut per&or$ opposite &unctions It is through theuse o& these de!ices that the co$puter is a%le to co$$unicate with the outside world Input data$a" %e in an" one o& three &or$s(

• )anual inputs &ro$ a ke"%oard or console

• Analog inputs &ro$ instru$ents or sensors

• Inputs &ro$ a source on or in which data has pre!iousl" %een stored in a &or$ intelligi%le

to the co$puter

*o$puters can process hundreds o& thousands o& co$puter words or characters per secondThus# a stud" o& the &irst $ethod ,$anual input- re&lects the ina%ilit" o& hu$an+operatedke"%oards or ke"punches to suppl" data at a speed that $atches the speed o& digital co$puters

A high a!erage speed &or ke"%oard operation is two or three characters per second# that# whencoded to &or$ co$puter words# would reduce the data input rate to the co$puter to less than aco$puter word per second Since $ain&ra$e co$puters are capa%le o& reading se!eral thousandti$es this a$ount o& in&or$ation per second# it is clear that $anual inputs should %e $ini$i0ed to$ake $ore e&&icient use o& co$puter ti$e 3owe!er# as a rule# the ke"%oard is the nor$al input$edia &or $icroco$puters

Input data that has pre!iousl" %een recorded on paper tapes# $agnetic tapes# $agnetic disks# or&lopp" disks in a &or$ understood %" the progra$ $a" also %e entered into the co$puter Theseare $uch &aster $ethods than entering data $anuall" &ro$ a ke"%oard The $ost co$$onl" used

input de!ices in this categor" are $agnetic tape units# $agnetic disk dri!e units# and &lopp" diskdri!e units

Output in&or$ation is also $ade a!aila%le in three &or$s(

• 1ispla"ed in&or$ation( codes# nu$%ers# words# or s"$%ols presented on a displa" de!ice

like a cathode+ra" screen

• *ontrol signals( in&or$ation that operates a control de!ice# such as a le!er# aileron# or

actuator












• Recordings( in&or$ation that is stored in a $achine language or hu$an language on

tapes# disks# or printed $edia

1e!ices that displa"# store# or read in&or$ation include $agnetic tape units# $agnetic disk dri!eunits# &lopp" disk dri!e units# printers# and displa" de!ices

)AGNETI* TAPE 2NITS ,INP2TCO2TP2T-

The purpose o& an" $agnetic tape unit ,dri!e or de!ice- is to write data on or read data &ro$ a$agnetic tape ,&ig 6+/- Tape stores data in a se4uential $anner In se4uential processing# theco$puter $ust %egin searching at the %eginning and check each record until the desired data is&ound Like a tape cassette with recorded $usic# to pla" the &i&th song recorded# "ou $ust pla" or&ast &orward the tape past the &irst &our songs %e&ore "ou can pla" the &i&th

Figure 6+/ + )agnetic tape unit

Two reels are used# tape $o!es &ro$ a suppl" reel to a take+up reel ,%oth are $ounted on hu%s-Figure 6+/ shows the %asic tape dri!e $echanis$ The $agnetic oBide coated side o& the tapepasses directl" o!er the readCwrite head asse$%l"# $aking contact with the heads The $agnetictape unit reads and writes data in parallel channels or tracks along the length o& the tape asshown in &igure 6+/=# !iew A Each channel or track is used %" a readCwrite head ,one &or eachchannel-# as the tape $o!es across the $agnetic gap o& the head ReadCwrite heads $a" %eeither one gap or two gap as shown in &igure 6+/=# !iews 8 and * The one+gap head has onl"one $agnetic gap at which %oth reading and writing occur

The two+gap head has one gap &or reading and another &or writing Although the one gap issatis&actor"# the two+gap head gi!es increased speed %" checking while writing For eBa$ple# atape %eing written on passes o!er the write gap where the data is recorded# and then the data is



read as it passes o!er the read gap to $ake a co$parison ?ith this $ethod# errors are detectedal$ost instantl" ?hen "ou look closel" at &igure 6+/=# !iew 8 ,top !iew-# "ou will notice that thereis one readCwrite coil in the write head &or each channel ,or track- In this particular case# thereare se!en It is the electrical current &lowing through these coils that $agneti0es the iron+oBidecoating on the sur&ace o& the tape

Figure 6+/ + A %asic tape dri!e $echanis$

Figure 6+/= + ReadCwrite head asse$%lies



The $aDor di&&erences %etween $agnetic tape units are the speed at which the tape is $o!edpast the readCwrite head and the density o& the recorded in&or$ation You know that densit"descri%es the nu$%er o& %inar" digits# %"tes# or &ra$es we can record on an inch o& tape The$ost co$$on tape densities are .. and /#.. 8PI ,or FPI- Tape speed ,or tape $o!e$ent-!aries to a great eBtent# &ro$ less than 9. inches per second to $ore than /.. inches persecond 3ow &ast a tape unit reads and writes is speci&ied as the character trans&er rate which iscalculated %" $ultipl"ing the speed o& the $agnetic tape unit %" the character densit"

)AGNETI* 1IS 1RI5E 2NITS ,INP2TCO2TP2T-

)agnetic disk dri!e units are storage de!ices that read and write in&or$ation on the $agneti0edsur&aces o& rotating disks ,&ig 6+6.- The disks are $ade o& thin $etal# coated on each side sothat data can %e recorded in the &or$ o& $agneti0ed spots As the disks spin around like $usicrecords# characters can %e stored on the$ or retrie!ed in a direct $anner This direct accessingo& data has a %ig ad!antage o!er the se4uential accessing o& data It gi!es us &ast# i$$ediateaccess to speci&ic data without ha!ing to eBa$ine each and e!er" record &ro$ the %eginning Youcan direct the disk dri!e to %egin reading at an" point This is like the phonograph record# "ou canplace the needle at an" point and %egin pla"ing at an" point

Figure 6+6. + )agnetic disk dri!e unit



Located within each disk dri!e unit is a dri!e $otor that rotates the disk at a constant speed#nor$all" @#.. re!olutions per $inute ,rp$-; or# i& "ou pre&er# . re!olutions per second Therotational speed &or &lopp" disks is usuall" %etween @.. and 7.. rp$ %ecause o& their plastic%ase 1ata is written on the tracks o& a spinning disk sur&ace and read &ro$ the sur&ace %" one ormore ,$ultiple- readCwrite heads ?hen reading &ro$ and writing to hard disks ,rigid disks-# thereadCwrite heads float on a cushion o& air and do not actuall" touch the sur&ace o& the disk Thedistance %etween the head and the sur&ace !aries &ro$ a $illionth o& an inch to one+hal& $illiontho& an inch This distance is called the &l"ing height ?hen $ultiple disks ,platters- are packagedtogether as a unit in a disk pack# a nu$%er o& access arms and readCwrite heads are used toaccess %oth sur&aces o& each platter ,&ig 6+6/-The disk pack shown consists o& siB $etal disks$ounted on a central spindle 1ata can %e recorded on all sur&aces eBcept the top sur&ace o& thetop disk# and the %otto$ sur&ace o& the %otto$ disk These two sur&aces are intentionall" le&t %lank&or protection

Figure 6+6/ + )ultiple access ar$s# readCwrite heads used with disk packs



Link Bar 2

FLOPPY 1IS 1RI5E 2NITS ,INP2TCO2TP2T-

Flopp" disk dri!e units are ph"sicall" s$aller than $agnetic disk dri!e units and are t"picall" usedwith personal ,desktop- co$puters ,&ig 6+66- The unit consists o& a disk dri!e in which the diskrotates and a controller containing the electronic circuitr" that &eeds signals onto and &ro$ the

disk The disk ,diskette- is a thin# &leBi%le platter ,&lopp" disk- coated with $agnetic $aterial socharacters can %e recorded on the sur&ace in the &or$ o& $agneti0ed spots Flopp" disks co$e inse!eral si0es &ro$ @ to inches in dia$eter The $ost co$$on are the +inch disk# the 9 /C7+inchdisk# and the @ /C6+inch disk

Figure 6+66 + Flopp" disk dri!e unit



PRINTERS ,O2TP2T-

Printers are widel" used output de!ices that eBpress coded characters on hard ,paper docu$ent-

cop" ,&ig 6+6@- The" print out co$puter progra$ results as nu$%ers# letters# words# s"$%ols#graphics# or drawings Printers range &ro$ electronic t"pewriters to high+speed printers 3igh+speed printers are usuall" used on $ain&ra$es and $inis to prepare suppl" re4uisitions# pa"checks# in!entor"# or &inancial reports at /. lines per second and &aster The t"pes o& printers we'lldiscuss are dais"+wheel# dot $atriB# ink Det# and laser These are the ones co$$onl" used withpersonal co$puters

Figure 6+6@ + Printer



1ais"+?heel Printers

1ais"+wheel printers ha!e the $ost pro&essional+looking# pleasing+to+the+e"e print o& all theprinters in the character+at+a+ti$e i$pact printer class 1ais"+wheel printers are o&ten used in ano&&ice or word processing en!iron$ent# where crisp# sharp# high+4ualit" ,letter 4ualit"- charactersare a $ust The dais"+wheel printer uses a round disk# with e$%ossed characters located at theend o& each petal+like proDection ,one character per petal-# si$ilar to the petals o& a dais"# asshown in &igure 6+67 A dri!e $otor spins the wheel at a high rate o& speed ?hen the desiredcharacter spins to the correct position# the print ha$$er strikes that character causing it to %e

printed on the paper Once printed# the dais" wheel continues to $o!e# searching out the neBtcharacter to %e printed# until the line is co$pleted The speeds o& dais"+wheel printers range &ro$@. to . characters per second ,cps-

Figure 6+67 + A dais"+wheel print wheel



1ot+)atriB Printers

1ot+$atriB printers# ,also known as the wire matrix printers- create characters in $uch the sa$ewa" "ou see nu$%ers on the score%oard at a %ase%all or &oot%all ga$e In contrast to the dais"+wheel printers# dot+$atriB printers use an arrange$ent o& tin" pins or ha$$ers# called a dot$atriB# to generate characters a dot+at+a+ti$e A dot+$atriB print head %uilds characters out o& the

dots created %" the pins in the $atriB Figure 6+69# !iew A# shows what dot $atriB characters looklike when printed

Figure 6+69 + 1ot+$atriB printing



The dot $atriB is de&ined in ter$s o& rows and colu$ns o& dots A 9 %" $atriB uses up to &i!e!ertical colu$ns o& se!en dots to create a character An eBa$ple o& a 9 %" $atriB printing theletter is shown in &igure 6+69# !iew 1 The si0e o& dot $atriBes !aries &ro$ a 9 %" $atriB to aslarge as a 9 %" / $atriB A nu$%er o& dot+$atriB printers use a single !ertical colu$n o& pins toprint characters# as shown in &igure 6+69# !iew 8 The characters are printed %" $o!ing ,stepping-the print head a s$all a$ount and printing the !ertical colu$ns one at a ti$e until the character isprinted as shown in &igure 6+69# !iews * and 1

The si0e o& the $atriB deter$ines the 4ualit" o& the printed character In other words# the $oredots used to print a character# the %etter the character is &illed in and the higher its print 4ualit"1ot+$atriB printers are &aster than the dais"+wheel printers with speeds ranging &ro$ . to @9.cps# %ut their print 4ualit" is not as good

Ink et Printers

Ink Det printers e$plo" a techni4ue !er" si$ilar to the wa" we use a can o& spra" paint and a

stencil A spra" o& electricall" charged ink is shot ,under pressure- toward the paper 8e&orereaching the paper# the ink is passed through an electrical &ield which &or$s the letters in a $atriB&or$ The print resulting &ro$ this process consists o& eas" to read# high+4ualit" characters So$e$anu&acturers use large droplets o& ink &or &aster printing# while others use s$all droplets &or%etter clarit" %ut with slightl" reduced printing speeds These printers can print up to @.. cps

Laser Printers



Laser printers direct a %ea$ o& light through a rotating disk containing the &ull range o& printcharacters The appropriate character i$age is directed onto photographic paper# which is thenput through a toner# de!eloped# and used to $ake additional copies The print resulting &ro$ thisprocess consists o& sharp# clean i$ages that are eas" on the e"es These printers can print up to6.#... plus lines per $inute# or 6# cps ,characters per second-

EY8OAR1S ,INP2T-

A ke"%oard is nothing $ore than an arra" o& switches called ke"switches e"%oards aredesigned to input a code to the co$puter when a ke"switch is depressed Each ke"switch# or ke"#on the ke"%oard is assigned a particular code !alue; and it is usuall" i$printed with a legend toidenti&" its &unction Figure 6+6 shows a ke"%oard co$%ined with a crt on a $icroco$puter

Figure 6+6 + e"%oard co$%ined with a crt and $icroco$puter

The pri$ar" purpose o& a ke"%oard is to enter or input alphanumeric ,nu$%ers# letters# andspecial characters- character codes The $aDor grouping o& ke"switches on a ke"%oard will %e inone o& the two st"les o& a t"pewriter ke"%oard arrange$ent ,<?ERTY or 15ORA-

The t"pewriter ke"switches are arranged in 7 rows o& /. or $ore switches The ke"%oardarrange$ent shown in &igure 6+6 is <?ERTY The rows are usuall" o&&set to the row a%o!e to$ake it easier to reach all the ke"s when t"ping The tops o& the indi!idual ke"switches aresculptured to con&or$ to the shape o& the hu$an &inger

Figure 6+6 + e"%oard la"out



Other groupings o& ke"switches are used &or special purposes# such as nu$%er entr" ,calculator-ke"pads# special &unction switches ,F/+F/6-# and cursor control ke"s The special &unctionswitches allow an operator to use the special &unctions designed in the so&tware For eBa$ple# ina word processing progra$# "ou can use the$ to spell check a docu$ent# search &or a particularportion o& teBt# $o!e teBt &ro$ one place to another# and to print hard copies o& a docu$entThese are %ut a &ew o& the &unctions allowed; howe!er# as "ou %eco$e $ore &a$iliar withco$puters "ou will learn the$ all The cursor control ke" allows "ou to $o!e to di&&erent locationson the screen

The design o& ke"%oards !aries &ro$ de!ice to de!ice and is dependent on the re4uire$ents o&the s"ste$ in which the ke"%oards are installed

e"%oards are generall" used with nontactical co$puter s"ste$s 3owe!er# the newer tacticaldispla" s"ste$ consoles ha!e optional ke"%oards &or data entr" A ke"%oard $a" %e %uilt into the

displa" de!ice# or it $a" %e a separate co$ponent connected onl" %" a co$$unication ca%le

Link Bar 3

1ISPLAY 1E5I*ES

1ispla" de!ices are the crts and other displa"s that are part o& co$puter ter$inals# co$puterconsoles# and $icroco$puters The" are designed to proDect# show# eBhi%it# or displa" so&tcop"in&or$ation ,alphanu$erics or graphic s"$%olog"-

The in&or$ation displa"ed on a displa" de!ice screen is not per$anent That is where the ter$so&t+cop" co$es &ro$ The in&or$ation is a!aila%le &or !iewing onl" as long as it is on the displa"screen Two t"pes o& displa" de!ices used with personalC$icroco$puters are the raster scan crt'sand the &lat panel displa"s

Raster Scan *rts



Raster scan crts ,t! scan !ideo $onitors or displa" $onitors- are used eBtensi!el" in the displa"o& alphanu$eric data and graphics The" are used pri$aril" in nontactical displa" applicationssuch as SNAP II user ter$inals and desktop co$puters

The raster is a series o& hori0ontal lines crossing the &ace o& the crt screen ,&ig 6+6- Eachhori0ontal line is $ade up o& one trace o& the electron %ea$ &ro$ le&t to right The raster starts at

the top le&t corner o& the crt screen As each hori0ontal line is co$pleted# the %lanked electron%ea$ is rapidl" returned or retraced to the le&t o& the screen

Figure 6+6 + Raster or T5 scan

5ertical de&lection $o!es the %ea$ down# and the hori0ontal sweep repeats ?hen the !erticalsweep reaches the %otto$ line o& the raster# a !ertical %lanked retrace returns the sweep to thestarting position o& the raster# and the process is repeated

Each co$pleted raster scan is re&erred to as a field; two &ields $ake up a frame The displa" rateo& &ields and &ra$es deter$ines the a$ount o& &licker in the displa" that is percei!ed %" thehu$an e"e Each &ield is $ade up o& approBi$atel" 969 hori0ontal lines The actual nu$%er o&hori0ontal lines !aries &ro$ de!ice to de!ice A &ra$e consists o& the interlaced lines o& two &ields

The hori0ontal lines o& the two &ields are interlaced to s$ooth out the displa" A displa" rate o& @.&ra$es per second produces a s$ooth# &licker+&ree raster and corresponding displa" on thescreen

IC#*+% %,%%.#S + The actual displa" o& data results &ro$ the use o& picture ele$ents Apicture ele$ent is a !aria%le dot o& light deri!ed &ro$ !ideo signals input to the displa" $onitorThe picture ele$ents# o&ten called pixels or pels# are contained in the hori0ontal scan linescrossing the &ace o& the crt screen The hori0ontal and !ertical sweeps are continuous andrepetiti!e in nature



Pictures with alphanu$eric characters and graphics can %e created and displa"ed %" !ar"ing theintensit" or %rightness o& the picture ele$ent dots This is done in conDunction with the phosphorcoating on the &ace o& the crt

The nu$%er o& picture ele$ents in each hori0ontal line !aries &ro$ de!ice to de!ice The actualnu$%er o& picture ele$ents is dependent on the &re4uenc" %andwidth o& the !ideo $onitor# the

nu$%er o& characters to %e displa"ed on a line# and the ph"sical si0e o& the screen

Each picture ele$ent is addressa%le %" a row and colu$n address Picture ele$ents arenu$%ered &ro$ le&t to right on each hori0ontal line ,colu$n nu$%er- Each hori0ontal line has arow nu$%er Picture ele$ents# at a $ini$u$# will ha!e o&& ,%lanked- or on ,&ull intensit"- states)an" displa" de!ices ha!e the capa%ilit" to displa" picture ele$ents at !ar"ing degrees o&intensit" &or the displa" o& graphics

*haracters are asse$%led on the screen in $uch the sa$e wa" as a dot+$atriB print head printsa character It takes se!eral hori0ontal lines and picture ele$ents on each line to create acharacter Figure 6+6= shows the generation o& the character A# picture ele$ents wide and =hori0ontal lines high The character is %uilt using what is# in e&&ect# a %" = dot $atriB The pictureele$ents used to %uild the character would %e at &ull intensit"; the re$aining picture ele$ents in

the $atriB would %e %lanked I& dark characters on a lighted screen were desired# then thecharacter picture ele$ents would %e %lanked and the re$ainder displa"ed at &ull intensit"

Figure 6+6= + A %" = picture ele$ent character

ApproBi$atel" 7. picture ele$ents per hori0ontal line are re4uired &or the displa" o& an .character line There&ore# "ou can eBpect /7.#... picture ele$ents on a raster scan displa"screen ,. alphanu$eric characters per line and 69 lines-

"+I/".#0, 0.1 2%+#IC0, +%S",*#I". + 3ori0ontal resolution is de&ined in ter$s o& thenu$%er o& picture ele$ents that can %e displa"ed on the hori0ontal line without o!erlapping orrunning into each other It is o&ten stated in ter$s o& lines o& resolution In other words# a $onitor



with a hori0ontal resolution o& /#... lines can displa" /#... !ertical lines using /#... pictureele$ents per line

5ertical resolution depends on the nu$%er o& hori0ontal scan lines used %" the particular displa"raster Generall"# the greater the nu$%er o& scan lines# the easier it is to resol!e a hori0ontal lineo& displa" This characteristic re$ains true up to a point# called the $erge point# where the

!ariation %etween the lines cannot %e detected %" the hu$an e"e

1IS,03I.4 10#0 ". +0S#%+ SC0. SC+%%.S + Raster scan displa"s are repetiti!e innature The raster &ra$e is displa"ed approBi$atel" @. ti$es a second

The %asic !ideo $onitor does nothing $ore than displa" the !ideo signals it recei!es I& no !ideosignals are recei!ed# then all the picture ele$ents re$ain %lanked# and the screen is %lank ineach &ra$e For data to %e displa"ed accuratel"# each and e!er" &ra$e $ust %lank and un%lankthe sa$e picture ele$ents

The digital logic that dri!es !ideo $onitors is designed to take ad!antage o& the repetiti!e natureo& &ra$es There can onl" %e a &iBed nu$%er o& picture ele$ents on the screen o& a displa";there&ore# the contents o& the displa" screen are organi0ed into a data unit called a page

The page contains the status o& e!er" picture ele$ent on the displa" screen The page is usuall"stored in so$e &or$ o& rando$+access $e$or"# RA) chips %eing the $ost co$$on Thecontents o& page $e$or"# or# as it is so$eti$es called# !ideo $e$or"# are continuall" scanned%" the !ideo generation logic and used to de!elop the !ideo signals &or the picture ele$entdispla" The picture ele$ent locations in page $e$or" are read in ti$e to de!elop the !ideosignals &or the picture ele$ent displa" on the hori0ontal lines

I& the displa" is to %e changed# the contents o& page $e$or" $ust %e changed The displa" onthe screen changes as new data is stored in page $e$or" Two addressing $ethods are usedwith page $e$or"

*nformatted 1isplays + 1ispla"s that re&erence page $e$or" %" picture ele$ent address arecalled unformatted or fully populated displa"s These displa"s are $ore co$$onl" used &orgraphics rather than alphanu$eric characters

5ormatted 1isplays + O&ten displa"s are organi0ed %" character position and line nu$%erThese displa"s are known as formatted displa"s This displa" $ethod is used with de!icesdispla"ing alphanu$eric characters onl" or those with an alternate graphic capa%ilit"

The !ideo generation logic o& these t"pes o& displa"s scans the entire page $e$or"# as %e&ore# togenerate the displa" picture ele$ents The di&&erence is in the wa" the new data is written into thepage $e$or" Indi!idual picture ele$ent addresses are not used *haracter addresses are usedto re&erence page $e$or"

The screen is organi0ed into character lines Each line is $ade up o& a &iBed nu$%er o& characterpositions or colu$ns A &iBed nu$%er o& character lines can %e displa"ed A co$$onarrange$ent &ound on displa" screens is twent" &i!e .+character lines# or 6#... characters

The character set that can %e displa"ed on a de!ice's &or$atted screen is stored in RO)s orPRO)S That is# the dot+$atriB ,picture ele$ent- patterns &or each indi!idual character to %edispla"ed are stored 1i&&erent character sets $a" %e displa"ed %" si$pl" replacing theappropriate RO) or PRO) chips with new chips containing di&&erent character patterns



2pon receipt o& a character code and a row and colu$n address# the de!ice logic reads thepicture ele$ent pattern ,dot $atriB- &ro$ the RO) and writes the pattern into the appropriatecharacter position in the page $e$or" The desired character is then displa"ed at the correctposition Other displa" de!ices store the codes in page $e$or" and con!ert the codes to pictureele$ent dots when scanning $e$or" to re&resh or redispla" the characters on the screen Theuse o& &or$atted displa"s greatl" si$pli&ies the progra$$ing re4uire$ents &or the displa" o&alphanu$eric data

Flat Panel 1ispla"s

A nu$%er o& displa" $ethods are in use that are designed to reduce the depth o& the crt displa"caused %" the length o& the tu%e These de!ices are collecti!el" known as &lat panel displa"sThree t"pes o& &lat panel displa"s co$$onl" in use with co$puter s"ste$s are li4uid cr"staldispla"s ,L*1s-# gas plas$a displa"s ,GP1s-# and electrolu$inescent displa"s ,EL1s-

The screens o& these &lat panel displa"s are $ade up o& pairs o& electrodes Each pair o&electrodes is used to generate one picture ele$ent

The li4uid cr"stal displa" di&&ers &ro$ the gas plas$a and electrolu$inescent displa"s in that it

does not generate its own light &or the picture ele$ents The L*1 re4uires an eBternal lightsource# o&ten called a %acklight# &or co$puter applications The li4uid cr"stal $aterial %etween thecharged electrodes %eco$es translucent when !oltage is applied and allows the %acklight toshine through as a picture ele$ent

In the gas plas$a and electrolu$inescent displa"s# the picture ele$ent light is generated %"ioni0ing a gas ,neon or neon argon- %etween the charged electrodes ,gas plas$a displa"- or %"sti$ulating a lu$inescent $aterial in the sa$e $anner ,electrolu$inescent displa"- In eithercase# the picture ele$ent onl" e$its light when the electrodes ha!e !oltage applied to the$

One o& the ad!antages o& &lat panel displa"s is that s$aller !oltages are re4uired &or theiroperation than &or a crt Gas plas$a displa"s use approBi$atel" 6.. !olts to charge theelectrodes# and electrolu$inescent displa"s re4uire onl" 6. !olts

The picture ele$ents in these displa"s are addressed %" the row and colu$n $ethod 1ispla"swith as $an" as @#6. picture ele$ents ,=. rows %" colu$ns- ha!e %een de!eloped

The picture ele$ents on &lat panel displa"s are not lighted continuall" This would re4uire a largea$ount o& power and generate eBcessi!e heat A se4uential scan si$ilar to a crt raster is usedOnce again a page $e$or" is re4uired The picture ele$ent electrodes are on and o&& as thescan se4uentiall" addresses page $e$or"

Those picture ele$ents that are to displa" a dot are $o$entaril" turned on and o&& starting withthe &irst picture ele$ent in the top row# or line# and ending with the last picture ele$ent on the%otto$ row The picture ele$ents are turned on and o&& at a high enough &re4uenc" that the

hu$an e"e cannot detect the &licker o& the o&&+on+o&& c"cle

The se4uential scan used to light the picture ele$ents is continuous and repetiti!e Once again#the page $e$or" $ust %e changed to change the displa" Flat panel displa"s $a" %e &or$attedor un&or$atted in the sa$e $anner as crt displa"s

<@9 ?hat is the purpose o& an" $agnetic tape unit>

<@ ?hat are the $aDor di&&erences %etween $agnetic tape units>





<@ ?h" is direct accessing o& data a %ig ad!antage o!er the se4uential accessing o& data>

<@ ?hat is a &lopp" disk>

<@= ?hat are the three $ost co$$on si0es o& &lopp" disks><7. ?hat output de!ice eBpresses coded characters as hard cop" ,paper docu$ents->

<7/ ?hat &our t"pes o& printers are co$$onl" used with personal co$puters>

<76 ?hat is the pri$ar" purpose o& a ke"%oard>

<7@ Raster scan or t! scan !ideo $onitors are used eBtensi!el" &or what purpose>

<77 3ow $an" &ields $ake up a &ra$e>

<79 A &ield is approBi$atel" how $an" hori0ontal lines>

<7 ?hat are picture ele$ents o&ten called>

<7 5ertical resolution depends on what>

<7 Flat panel displa"s are designed to reduce what pro%le$ o& a crt displa">

<7= ?hat does the li4uid cr"stal displa" re4uire &or co$puter applications>

Link Bar 4

SOFT?ARE

LEARNING O8E*TI5ES

2pon co$pletion o& this chapter# "ou will %e a%le to do the &ollowing(

• Recogni0e and co$pare the di&&erent t"pes and &unctions o& operating s"ste$s• Identi&" the t"pes o& utilities and eBplain their &unctions

• 1escri%e the di&&erent t"pes and &unctions o& progra$$ing languages

• EBplain the steps necessar" to de!elop a progra$ and descri%e the tools used

• *o$pare and descri%e the t"pes and &unctions o& applications packages

INTRO12*TION

2p to now we ha!e %een discussing co$puter "%+0#I".0, C".C%#S and 0+160+%(the computer and its peripheral devices)7 and how these devices work and communicatewith each other 6hat about this thing called S"5#60+%8 1o we really need it8 6e mostcertainly do9 Software plays a ma:or role in computer data processing 5or example7

without software7 the computer could not perform simple addition It;s the software thatmakes everything happen "r putting it another way7 software brings the computer to life

You alread" know it takes a progra$ to $ake the co$puter &unction You load an operatings"ste$ into the co$puter to $anage the co$puter's resources and operations You gi!e Do%in&or$ation to the operating s"ste$ to tell it what "ou want the co$puter to do You $a" tell it toasse$%le or co$pile a *O8OL progra$ You $a" tell it to run the pa"roll or print in!entor"reports You $a" tell it to cop" a tape using a utilit" progra$ You $a" tell it to print the data &ro$a disk &ile# also using a utilit" progra$ You $a" tell it to test a progra$ This Do% in&or$ation $a"%e entered through the console or read into the co$puter &ro$ tape or disk It also $a" %e

















entered %" the progra$$er or user &ro$ a re$ote co$puter ter$inal The operating s"ste$recei!es and processes the Do% in&or$ation and eBecutes the progra$s according to that Do%in&or$ation

So&tware can %e de&ined as all the stored progra$s and routines ,operating aids- needed to &ull"use the capa%ilities o& a co$puter Generall" speaking# we sa"# :I& it is not hardware then it $ust

%e software:

OPERATING SYSTE)S

The operating s"ste$ is the heart o& an" co$puter s"ste$ Through it# e!er"thing else is done8asicall"# operating s"ste$s are designed to pro!ide the operator with the $ost e&&icient wa" o&eBecuting $an" user progra$s

An operating s"ste$ is a collection o& $an" progra$s used %" the co$puter to $anage its ownresources and operations These progra$s control the eBecution o& other progra$s The"schedule# assign resources# $onitor# and control the work o& the co$puter There are se!eralt"pes

TYPES OF OPERATING SYSTE)S

Operating s"ste$s are designed to pro!ide !arious operating $odes So$e s"ste$s can onl" doone task at a ti$e# while others can per&or$ se!eral at a ti$e So$e s"ste$s allow onl" oneperson to use the s"ste$# and others allow $ultiple users Single user&single tasking operatings"ste$s are the si$plest and $ost co$$on on $icroco$puters C&-<=/# C&-<>/# and S-1"S(?7@)6 are eBa$ples Single user&multitasking operating s"ste$s allow "ou to do $ore thanone task as long as the tasks don't use the sa$e t"pe o& resources For eBa$ple# "ou can printone Do% while "ou run another# as long as the second Do% does not re4uire the printer EBa$plesare Concurrent C&-<>@# Concurrent 1"S@# and S-1"S ,@. and a%o!e-)ultiuserC$ultitasking operating s"ste$s let $ore than one user access the sa$e resources atthe sa$e ti$e This is especiall" use&ul &or sharing co$$on data These are onl" &easi%le onprocessors ,the &unctional unit in a co$puter that interprets and eBecutes instructions- o& / %its

or $ore and with large $e$ories *.IA7 is an eBa$ple There are also multiprocessorsystems7 shared resource s"ste$s This $eans each user ,or operator- has a dedicated$icroprocessor ,cpu-# which shares co$$on resources ,disks# printers# etc-

/*PC) and *PC)+ are registered trade$arks o& 1igital Research Inc

6)S+1OS is a registered trade$ark o& )icroso&t *orporation

@*oncurrent *PC) and *oncurrent 1OS are trade$arks o& 1igital Research Inc

72NIH is a trade$ark o& AT J T

*O)PATI8ILITY ?IT3 APPLI*ATIONS SOFT?ARE

To use an applications progra$# it $ust %e co$pati%le with the operating s"ste$ There&ore# thea!aila%ilit" o& application so&tware &or a particular operating s"ste$ is critical 8ecause o& this#se!eral operating s"ste$s ha!e %eco$e the $ost popular For +%it $icroco$puters# C&,*ontrol Progra$ &or )icroprocessors- is widel" used %ecause $an" hardware $anu&acturersha!e adopted it S-1"S ,)icroSo&t 1isk Operating S"ste$- designed &ro$ *PC) do$inates inlower per&or$ance /+%it s"ste$s *.IA# an operating s"ste$ &or larger co$puters# is %eing used



on the $ore power&ul /+%it and @6+%it $icroco$puters Other operating s"ste$s are o&&ered %"$icroco$puter $anu&acturers

To o!erco$e the applications so&tware co$pati%ilit" pro%le$# so$e so&tware co$es in se!eral!ersions so it can %e run under se!eral di&&erent operating s"ste$s The point to re$e$%er is thatnot all applications so&tware will run on all s"ste$s You ha!e to check to see that co$pati%ilit"

eBists You need the right !ersion

OPERATING SYSTE) F2N*TIONS

To gi!e "ou a %etter idea o& what "ou can eBpect to see on "our $icroco$puter displa" screen#we will show a &ew &unda$ental disk operating s"ste$ co$$ands and $essages Again# the&unctions o& each operating s"ste$ are a%out the sa$e# %ut each $a" use a di&&erent co$$andto do a%out the sa$e thing For eBa$ple# tr" not to get con&used %ecause C& uses theco$$and I ,peripheral interchange progra$- to cop" a &ile# while S-1"S uses the co$$andC"3

Re$e$%er# the &irst thing "ou need to do is %oot ,initial progra$ load- the s"ste$ There are$an" wa"s this can %e done 3ere is an eBa$ple ?hen "ou turn on the power# a pro$pt $a"

appear on the screen You then insert the operating s"ste$ &lopp" disk into the dri!e 0 T"pe a B,&or %oot- and press the +%#*+. ke" The operating s"ste$ will load &ro$ the disk I& "ou areusing a s"ste$ set up &or auto$atic %ooting# "ou won't ha!e to t"pe the 8 The s"ste$auto$aticall" loads the operating s"ste$ when "ou insert the disk that contains it So$e s"ste$swill then ask &or date and ti$e Enter these You will neBt see a pro$pt# usuall" 0 (or 0) Thes"ste$ is read" and dri!e A is assigned as "our pri$ar" dri!e One thing "ou $ight want to do isto displa" the disk director" to see what is on the disk To do this# enter 1I+ &ollowing the 0This will list "our &iles

*O))AN1*O)

*ONFIG2R*O)

1AT18L8A

1AT18L1O*

FINAN*E8AS

)ASTER1O*

It $a" also gi!e "ou &ile si0e and the date and ti$e o& the &ile Let's take an eBa$ple Let's sa""ou are to cop" the &ile :)ASTER1O*: &ro$ the &lopp" disk in dri!e 0 to the &lopp" disk in dri!eB and then delete the &ile on the &lopp" disk in dri!e 0 You ha!e Dust displa"ed the director" o&the &lopp" disk in dri!e 0 *heck to see that the &ile "ou want is on the &lopp" disk in dri!e 0 It isYou then insert the &lopp" disk on which "ou want the cop" into dri!e B 8e sure it is &or$attedwith the track and sector in&or$ation so it is read" to recei!e data Also# %e sure the disk is notwrite+protected On a 9+/C7 inch &lopp" disk that $eans the write protect notch is unco!eredFollowing the 0 t"pe

C"3 0S#%+1"C B and press +%#*+. The s"ste$ will cop" the &ile and gi!e it the sa$ena$e NeBt "ou $ight want to displa" the director" on dri!e 8 to see that the &ile was copied Youcan do this %" entering 1IR 8( &ollowing the AK pro$pt To delete the &ile on the &lopp" disk indri!e A# t"pe

1%, 0S#%+1"C &ollowing the 0 pro$pt on the screen and press +%#*+.



You pro%a%l" noticed each entr" in the director" is &ollowed %" three characters These are calledextensions# and we use the$ to tell us the t"pe o& &ile we are working with For eBa$ple#

B0D $eans %ackup &ileB0S $eans 8ASI* source progra$# $eans te$porar" &ile

1"C $eans AS*II docu$ent &ileBI. $eans %inar" &ile# and so on

Other t"pical %uilt+in operating s"ste$ co$$ands "ou can use $ight include(

RENA)E to change the na$e o& a &ile

1IS*OPY to cop" a whole &lopp" disk

FOR)AT to initiali0e a &lopp" disk# get it read" to recei!e data and progra$s &ro$ the s"ste$

TI)E to displa" or set the ti$e

You will learn to use these and $an" other system commands as "ou operate a speci&icco$puter

?e won't go into an" $ore detail here You will ha!e docu$entation and re&erence $anuals &orthe speci&ic !ersion o& the operating s"ste$ "ou will %e using

</ ?hat is the heart o& an" co$puter s"ste$>

<6 ?hich t"pes o& operating s"ste$s are the si$plest and $ost co$$on on $icroco$puters><@ ?hat t"pes o& operating s"ste$s let $ore than one user access the sa$e resources at thesa$e ti$e><7 ?h" is the a!aila%ilit" o& applications so&tware &or a particular operating s"ste$ critical><9 3ow is the applications so&tware co$pati%ilit" pro%le$ o!erco$e>

types of internal storage.doc

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