gcse ict revision notes- part 2

7/28/2019 GCSE ICT Revision Notes- Part 2

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GCSEICTREVISIONNOTES- PART2

COMPUTERSYSTEMS

3TYPESOFCOMPUTERSYSTEM

Informationsystems

ThistypeofICTsystemisfocusedonmanagingdataandinformation.

Examplesoftheseareasportsclubmembershipsystemorasupermarket

stocksystem.Controlsystems

TheseICTsystemsmainlycontrolmachines. Theyuseinput,processand

output,buttheoutputmaybemovingarobotarmtoweldacarchassisrather

thaninformation.

Communicationssystems

TheoutputoftheseICTsystemsisthesuccessfultransportofdatafromone

placetoanother.

Input,outputandsystemdiagrams

WhatcomesoutofanICTsystemislargelydependantonwhatyouputintothe

systemtobeginwith.

ICTsystemsworkbytakinginputs (instructionsanddata),processingthem

andproducingoutputsthatarestoredorcommunicatedinsomeway. The

higherthequalityandbetterthought-outtheinputs,themoreusefulthe

outputs.

GarbageIn,GarbageOut (GIGO)

ICTsystemscannotfunctionproperlyiftheinputsareinaccurateorfaulty;

theywilleithernotbeabletoprocessthedataatall,orwilloutputdatawhichiserroneousoruseless.

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GIGOisausefultermtorememberintheexam - itcanhelpexplainmany

issuessuchaswhyvalidationisneededandwhyaccuratedataisvaluable.

GIGOstandsforGarbageIn,GarbageOut

AnICTsystemdiagram

Asystemisanassemblyofpartsthattogethermakeawhole. ICTsystemsare

madeupofsomeorallofthepartsshowninthediagram. Variousdevicesare

usedforinput,processing,output,andcommunication.

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HARDWAREAND

SOFTWARE

HARDWARE

INPUTANDOUTPUTDEVICES

INPUTDEVICES - Inputdevicesallowustoenterrawdataintoacomputer.

Thecomputerprocessesthedataandthenproducesoutputsthatwecan

understandusinganoutputdevice. Inputdevicescanbemanualor

automatic.

Examplesofinputdevices- Conceptkeyboard

Eachbuttononaconceptkeyboardrelatestoaparticularitemorfunction.

Buttonscanbelabelledwithtextorapicture. Fastfoodrestaurantsoftenuse

conceptkeyboardsbecauseverylittletrainingisneededtooperatethemand

they' reefcient - asinglebuttoncanorderanentiremeal.

Trackball

Usedasanalternativetoamouse. Tooperateittheuserrotatestheballwhich

movesthepointeronscreen. Theyareparticularlyeasytouseforthosewith

limitedmovementintheirhandsandareoftenusedinComputerAidedDesign

(CAD) fortheirincreasedprecisionoveramouse.

Joystick

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Joysticksusedtobepopularwithgamersbuthaveslowlybeenreplacedby

othertypesofgamecontroller. Inconstruction,joysticksareusedtocontrol

machinerysuchascranes.

Digitalcamera

Adigitalcameratakespicturesandcanusuallyrecordvideotoo. Thepictures

ittakesandthevideositrecordsarestoredinfiles. Thesefilescanbecopied

toacomputerandlateredited.

Microphone

Microphonesareusedtoinputsound. Incomputingtheycanbeusedwith

voicerecognitionsoftwareandawordprocessingapplicationtoentertext.

Webcamscommonlyhavemicrophonesbuilt-intoo.

Touchscreen

Atouchsensitivevisualdisplayunit (VDU) orscreenhasagridoflightbeams

orfinewirescriss-crossingthescreenthatareusedtodetecttouch. Many

mobilephonesusetouchscreensanddoawaywiththekeypadentirely.

They' reoftenusedoncashmachinesandinshoppingcentrestoo. Touch

screensarerobust,easytooperateandeasytoreprogram.Videodigitiser

Avideodigitisertakesanimagefromavideocameraortelevisionand

digitisesitsoitcanbereadby,andstoredon,acomputer. Videosequences

capturedusingavideodigitiserareoftenusedinmultimediapresentations.

Scanner

Ascannercanbeusedtodigitiseimages. They' resimilartoaphotocopierbut

theymakeadigitalcopyinsteadofaphysicalcopy. Theycanalsobeusedwith

opticalcharacterrecognition (OCR) softwaretoscanintextthatisthen

editable.

Graphicstablet

Agraphicstabletconsistsofaflatpad (thetablet) onwhichtheuserdraws

withaspecialpen. Astheuserdrawsonthepadtheimageiscreatedonthe

screen. Usingagraphicstabletadesignercanproduceveryaccurateon-

screendrawingsasiftheyweredrawingonpaper.

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OUTPUTDEVICES-

Commonoutputformatsareprintedpaper,sound,videoandon-screen

documents. Theyletthecomputercommunicatewiththeuser. Examplesof

devicesthattakeadvantagesoftheseformatsare:

Monitor

ThemostcommonoutputdeviceisthemonitororVDU.

Modernmonitors,wherethecaseisntmorethanafewcentimetresdeep,are

usuallyLiquidCrystalDisplays (LCD) orThinFilmTransistors (TFT) monitors.

Oldermonitors,wherethecaseislikelytobearound30cmdeep,areCathode

RayTube (CRT) monitors.

Printers

1 Laserprintersarequiteexpensivetobuyandrunbutproduceahigh

qualityoutputandarequietandfast.

2 Ink-jetprintersoerblackandwhiteorcolourprintingwithreduced

levelsofqualityandspeed. Colourinkjetprintersarecheapertobuythancolourlaserprinters.

3 Dotmatrixprintersarenotsocommontoday. Theyarecomparatively

noisyandlowqualitybutarecheaptorunandareusedwhencarbon

copiesorduplicatesneedtobemade,suchasforwageslips. Also,they

areusefulindirtyenvironmentssuchasagaragebecausetheyaremuch

sturdierthantheothertwotypesofprinter.

Plotters

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Aplottercanbeusedtoproducehighquality,accurate,A3sizeorbigger

drawings. TheyareusuallyusedforComputerAidedDesign (CAD) and

ComputerAidedManufacture (CAM) applications,suchasprintingoutplans

forhousesorcarparts.

Otheroutputdevices

OTHERTYPESOFOUTPUTDEVICES:

1 speakers

2 projectors

3 buzzers

4 motors

5 switchedoutputs

6 lights

7 mechanicaldevices

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ROMandRAM

Acomputerusestwotypesofstorage. AmainstoreconsistingofROMand

RAM,andbackingstoreswhichcanbeinternal,egharddisk,orexternal,ega

CDorUSBflashdrive.

Mainstore (orcomputermemory) isdividedintoReadOnlyMemory (ROM)

andRandomAccessMemory (RAM).

ROM

ROMismemorythatcannotbechangedbyaprogramoruser. ROMretainsits

memoryevenafterthecomputeristurnedo. Forexample,ROMstoresthe

instructionsforthecomputertostartupwhenitisturnedonagain.

RAM

RAMisafasttemporarytypeofmemoryinwhichprograms,applications

anddataarestored. Herearesomeexamplesofwhat' sstoredinRAM:

1 theoperatingsystem

2 applications

3 thegraphicaluserinterface (GUI)

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STORAGECAPACITIESANDFILESIZES

Storagecapacitiesandfilesizesaremeasuredfromlowesttohighestin:

1 bits2 bytes

3 kilobytes

4 megabytes

5 gigabytes

6 terabytes

Anoperatingsystemabbreviatesthesemeasurements,eg1megabyte

becomes1MB (megabyte).

Relationshipbetweenmeasurements

Thetablebelowoutlinestherelationshipbetweenbits (smallest) and

terabytes (largest). Readeachrowofthetablefromlefttoright:

Relationshipbetweenmeasurement

Size Equalto

8bits 1byte

1024bytes 1kilobyte

1024kilobytes 1megabyte

1024megabytes 1gigabyte

1024gigabytes 1terabyte

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SOFTWARE

Wordprocessingapplicationsallowuserstotypeandedittext.

Desktoppublishing (DTP) applicationsallowuserstocreatepagelayouts

usingtextandpictures.

Wordprocessing

MostpeoplearefamiliarwithwordprocessingpackagessuchasMicrosoft

WordorWriter (partoftheOpenOf

cesuite).Standardfeatures

Allwordprocessingapplicationsallowyouto:

1 enterandedittext

2 save

3 print

4 cut/copy/paste

5 checkyourspellingCut,copy,andpaste

Cutandcopyworkinasimilarway. Highlightingapieceoftext,right-clicking

andselectingcopy/cutwillstorethetextinmemory. Thedierenceiscopy

leavesthehighlightedtextbehindwhereascutremovesit. Toinsertthe

copied/cuttextintoadierentareaofthedocument,adierentdocument,or

anentirelydierentapplicationaltogether,right-clickandselectpaste.

Theuseofcut,copy,andpasteisnotnecessarilylimitedtotext.

Textformatting

Formattingtextmakesadocumenteasiertoread. Youcan:

1 changefonttypeandsize

2 changethealignmentoftext (left,centre,rightorjustified)

3 boldtext

4 underlinetext

5 createbulletedornumberedlists

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GRAPHICSSOFTWARE- BITMAPAND

VECTORIMAGES

Therangeofpictures,drawingsandimageswhichcanbeproducedbya

computerarecalledgraphics. Themaintypesofgraphicspackagesare

painting,drawing,photoeditingandCAD. Theremaybesomecrossover

betweenthepackages,iecertainpackagesmaybesuitableformorethan

onetask.

Paintingpackages

Apaintingapplicationallowsfreehanddrawingandcolouring,usuallywitha

mouse. Generallythefeaturesare:

1 apalettefromwhichtheusercanchoosecolours

2 freehandpensandbrushesoeringdierentstylesandlinethickness

3 arangeofstandardshapetoolssuchasrectanglesandcircles

4 colourfilltools

5 spraycansanderasertools

6 cut,copyandpaste

7 zoom (toworkinfinerdetail)

Bitmapgraphics

Bitmapgraphicsmadewithpaintingpackagesconsistofmanytinydotscalled

pixels. Itispossibletoediteachindividualpixel.

Sincethecomputerhastostoreinformationabouteverysinglepixel (the

colourforexample) intheimage,thefilesizeofabitmapgraphicisoften

quitelarge. Bitmapgraphicslosequalitywhenthey' reresized.

Vectorgraphics

Vectorgraphicsarebasedonmathematicalrelationshipswithcontrolpoints

thatmakeuptheimage,informationisnotstoredabouteachpixel. These

pointsareconnectedbylinesandcurvescalledvectorpathsorvectors.

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Vectorobjects

Avectorobjectisashapemadeupofvectorpaths. Itispossibletoediteach

objectseparately,forexample,changetheshape,stroke,fill,sizeand

position. Astrokefollowstheoutlineofthevectorpathandafilladdsacolour

totheareainsidethepath.

Advantages

1 Smallerfilesize - vectorgraphics,unlessbitmapimages,donotstore

dataabouteachindividualpixel. Foralargeillustration,suchasa

poster,avectorgraphicwouldhaveasignificantlysmallerfilesize

comparedtoabitmapimage.

2 Scalable - whenyouresizeavectorgraphicthemathematical

relationshipsmeanthattheimagedoesnotlosequality. Avector

graphicthesizeofapostagestampcouldberesizedtobeusedona

posterandtheimagewouldstillbeclear.

Disadvantage

Vectorgraphicsarenevergoingtobeaslife-likeasbitmapsorphotos. They

willalwaysappearcomputergenerated.

ComputerAidedDesign (CAD)

CADpackagesaremoresophisticateddrawingpackages. Theyareusedby

engineers,architectsanddesignerstoproducedetaileddesignplans

andtechnicaldrawings. CADsoftwareoersallthefeaturesofstandard

drawingsoftwarebutinadditionmayalsooer:

1 greateraccuracy (itispossibletoworktowithin1/72ofaninch)

2 objectsanddrawingscanbecreatedin2D,3D,2DCADand3DCAD

3 imagescanbeviewedfromanyangle

4 powerfulscaling,rotationandreflectionoptions

5 librariesofengineeringcomponentswhichcanbeimported

6 linkstopackagestocalculatecosts

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OPERATINGSYSTEMS

Anoperatingsystemisasystemprogramthatcontrolsandorganisesthe

generaloperationofthecomputer.

Operatingsystemfunctions

Inanycomputer,theoperatingsystem:

1 controlsthebackingstoreandperipheralssuchasscannersandprinters

2 dealswiththetransferofprogramsinandoutofmemory

3 organizestheuseofmemorybetweenprograms

4 organizesprocessingtimebetweenprogramsandusers

5 maintainssecurityandaccessrightsofusers

6 dealswitherrorsanduserinstructions

7 allowstheusertosavefilestoabackingstore

8 providestheinterfacebetweentheuserandthecomputer - for

example,WindowsVistaandAppleOSX.

9 issuessimpleerrormessages

GUI-GRAPHICALUSERINTERFACE

AnacronymtorememberwhatisincludedinaGUIisWIMP

WINDOWS - arectangularareaonthescreenwherethecommonlyused

applicationsrun

ICONS - apictureorsymbolwhichisusedtorepresentasoftwareapplication

orhardwaredevice

MENUS - alistofoptionsfromwhichtheusercanchoosewhattheyrequire

POINTERS - asymbolsuchasanarrowwhichmovesaroundthescreenasyou

moveyourmouse. helpsyoutoselectobjects.

BY BEN SANDERS
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NETWORKSANDCOMMUNITCATIONS

Acomputernetworkisanumberofcomputerslinkedtogethertoallow

themtoshareresources. Networkedcomputerscanshare

hardware,softwareanddata.

Mostcomputernetworkshaveatleastoneserver. Aserverisapowerful

computerthatprovidesoneormoreservicestoanetworkanditsusers.

Forexample,filestorageandemail.

LANsandWANs

Therearetwomaintypesofnetwork:

1. LocalAreaNetworkLAN

2. WideAreaNetworkWAN

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LAN

ALANcoversasmallareasuchasonesiteorbuilding,egaschooloracollege.

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WAN

AWANcoversalargegeographicalarea. MostWANsaremadefromseveral

LANsconnectedtogether.

WAN - WideAreaNetwork

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1 TheInternetisaWAN.

2 AnetworkofbankcashdispensersisaWAN.

3 AschoolnetworkisusuallyaLAN.

4 LANsareoftenconnectedtoWANs,forexampleaschoolnetworkcould

beconnectedtotheInternet.5 WANscanbeconnectedtogetherusingtheInternet,leasedlinesor

satellitelinks.

Advantages and disadvantages of networks

Advantages

1 Sharing devices such as printers saves money.

2 Site (software) licenses are likely to be cheaper than buying several

standalone licenses.

3 Files can easily be shared between users.

4 Network users can communicate by email and instant messenger.

5 Security is good - users cannot see other users' files unlike on

stand-alone machines.

6 Data is easy to backup as all the data is stored on the file server.

Disadvantages

1 Purchasing the network cabling and file servers can be expensive.

2 Managing a large network is complicated, requires training and a

network manager usually needs to be employed.

3 If the file server breaks down the files on the file server become

inaccessible. Email might still work if it is on a separate server. The

computers can still be used but are isolated.

4 Viruses can spread to other computers throughout a computer

network.

5 There is a danger of hacking, particularly with wide area networks.

Security procedures are needed to prevent such abuse, eg a

firewall.

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TYPESOFNETWORK

BUSNETWORK

RINGNETWORK

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STARNETWORK

BY BEN SANDERS

gcse ict revision notes- part 2

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