GCSE_ICT.PPT - Revision World.ppt

Computers,data and information,1,A computer is an information processing machine.Computers process data to produce information.The sets of instructions that humans give computers are called programs or software.Software that carries out a particular type of task for a user is often called applications software.,Computers can work much faster than humans;Computers never get tired or need a rest;Computers can do jobs that it would be dangerous for a human to do;Computers can store large amounts of information in a very small space;Computers can find information very quickly;Computers never lose or misplace information.,There are many reasons for using computers:-,The three stages of computing are input,processing and output.A computer works through these stages by running a program.A program is a set of step-by-step instructions which tells the computer exactly what to do with input in order to produce the required output.,Input,This stage of computing is concerned with getting the data needed by the program into the computer.Input devices are used to do this.The most commonly used input devices are the mouse and the keyboard.,Processing,The instructions about what to do with the input are contained in a program.During the processing stage the computer follows these instructions using the data which has just been input.What the computer produces at the end of this stage is called output.,Output,This stage of computing is concerned with producing the processed data as information in a form that is useful to the user.Output devices are used to do this.The most commonly used output devices are the screen,which is also called a monitor or visual display unit(VDU)and the printer.,Data and information,Data is any collection of numbers,characters or other symbols that has been coded into a format that can be input into a computer and processed.Data on its own has no meaning,or context.It is only after processing by a computer that data takes on a context and becomes information.,All data ends up being stored as a series of numbers inside the computer.Data can be input to the computer by the user in many different ways.The main types of data that can be input into a computer and processed are numeric,text,dates,graphics and sound.,There are many types of data.,Computer Systems,Hardware is the name that is given to any part of a computer that you can actually touch.An individual piece of hardware is called a device.The basic hardware of any computer consists of a central processing unit(CPU)along with input,output and backing storage devices.,The central processing unit(CPU),This is the part of the computer where the searching and sorting of data,calculating and decision-making goes on.The CPU contains the Main Memory,the Control Unit and the Arithmetic and Logic Unit(ALU).,Manual Input Methods,2,Manual input devices are used by people to enter data by hand.KeyboardPointing devicesJoystickDigital cameraTouch screenScannerConcept keyboardGraphics tabletMicrophoneLight pen,Keyboard,The keyboard is the most common type of input device.Ordinary computer keyboards have their keys arranged in a similar way to those on a typewriter.This way of arranging the keys is called QWERTY because of the order that the keys appear in on the first row of letters.,Pointing devices,A mouse is a pointing device.It is the next most common type of input device after the keyboard.,Touch pads and trackballs are also types of pointing device.They are often used instead of a mouse on portable computers.,Joystick,The main use of a joystick is to play computer games by controlling the way that something moves on the screen.Joysticks can be used to control movement from side-to-side,up-and-down and diagonally.A joystick will also always have at least one button on it which can be used to make something happen like making a character in a game jump or fire a gun.,Touch screen,A touch screen can detect exactly where on its surface it has been touched.Touch screens are used in a lot of fast food chains and restaurants because they are easy to keep clean and re-program if changes need to be made to the menu.,Digital camera,A digital camera can store many more pictures than an ordinary camera.Pictures taken using a digital camera are stored inside its memory and can be transferred to a computer by connecting the camera to it.A digital camera takes pictures by converting the light passing through the lens at the front into a digital image.,Scanner,A scanner can be used to input pictures and text into a computer.There are two main types of scanner;Hand-held and Flat-bed.,Concept keyboard,A concept keyboard is a flat board with a grid of programmable keys on its surface.A single key or a group of keys can be set up to carry out a particular task.Paper overlays are placed on top of the keyboard with pictures drawn on them to represent what will happen if the keys in a certain position are pressed.Concept keyboards are often used with young children in primary schools who cant use an ordinary keyboard very well.,Graphics tablet,When the special pen touches the surface of the graphics tablet data about its position is sent to the computer.This data is used to produce on the screen an exact copy of what is being drawn on the surface of the graphics tablet.,A graphics tablet consists of a flat surface and a pen,or stylus,which can be used to produce freehand drawings or trace around shapes.,Microphone,A microphone is used to input sound into a computer system.Microphones are often used for voice recognition systems which convert sounds made by a user into commands that the computer can carry out.Systems like this are very useful for people who cant use ordinary input devices such as the mouse and keyboard.As computers become more powerful in the future,voice recognition will be a much more common input method for all computer users.,Light pen,A light pen is a small pen-shaped wand,which contains light sensors.It is used to choose objects or commands on the screen either by pressing it against the surface of the screen or by pressing a small switch on its side.A signal is sent to the computer,which then works out the light pens exact location on the screen.The advantage of a light pen is that it doesnt need a special screen or screen coating.,Direct Input Methods,3,Methods of capturing and entering data directly without any need for human intervention.Sometimes called direct data entry,or DDE for shortUsed when very large amounts of data need to be input quickly and accurately.,Optical Mark Recognition(OMR),OMR uses an input device called an optical mark reader to detect marks made in certain places on specially printed forms.A fast input method,used where large amounts of data need to be input quickly.Used to input data from things like answer sheets for multiple choice exams and registration forms in schoolsAlso National Lottery forms,Magnetic Ink Character Recognition(MICR),MICR uses an input device called a magnetic ink character reader to input characters that have been printed in special magnetic inkBanks use MICR to process chequesBanks use this method of input for processing cheques because it is very secureThe equipment needed to print and read characters in magnetic ink is very expensive,Optical Character Recognition(OCR),OCR is the use of an ordinary scanner and special software to convert text in a scanned image into a format that can be edited by word processing softwareText must be printed or written very clearlyUsed for the reading of typed postcodesOCR depends on the shape of the marks whereas OMR depends on the position of the marks,Bar codes,A bar code is a set of lines of different thicknesses that represent a numberBar Code Readers are used to input data from bar codes.Most products in shops have bar codes on themBar code readers work by shining a beam of light on the lines that make up the bar code and detecting the amount of light that is reflected backBar codes represent a code number for a product,Magnetic stripe readers,A magnetic stripe is a thin band of magnetic tape Often on the back of a credit or debit card,identity cards and electronic key cards in hotels and businessesMagnetic stripes can hold only a small amount of data and are quite easy to forge In the next few years magnetic stripes will be replaced with smart cards which store much more data on a small microchip built into the surface of the card,Sensors,Sensors are used to detect physical quantities outside a computer such as temperature,pressure and light To be able to process input from sensors a device called an analogue-to-digital converter must be connected between the computer and the sensors.This device converts signals from sensors into digital data that the computer can process.,Data logging,Data logging is a way of using a computer to automatically collect data over a period of time without any need for human supervisionUseful when data needs to be collected in remote or inhospitable conditions where it would be difficult for humans to take measurementsUsed in weather monitoring stations and in science experiments,Applications of data logging,Collecting scientific dataMonitoring hospital patientsCollecting weather dataMonitoring air quality,Checking data,4,Data stored on a computer is only useful as long as it is correct and up-to-date.it is important to check data when it is entered to make sure that it is both sensible and correct.If data is not checked before it is processed any errors could cause the final output to be nonsense.There are two methods that can be used to check data when it is input.These are called verification and validation.,Verification is checking to make sure that data has been entered correctly.Verification is often carried out by getting two users to enter the same set of data at different computers.Once both users have entered the data the two sets of data are compared to check that they match up.Any data that does not match up is rejected.Verification can also be carried out by software which might,for example,ask for the same data to be entered twice.If both entries dont match up the data is rejected.,Verification,Validation checks are carried out by software to make sure that data which has been entered is allowable and sensible.Data that is not sensible or allowed is rejected by the computer.There are many different types of validation check that software can make on data.We will now look at some of these in more detail.,Validation,Range checkRange checks are used to check that data is within a certain range of numbers or a specific set of values.For example if the examination marks for a group of students was being input a range check could be used to make sure that each mark was greater than or equal to zero and less than or equal to the maximum possible mark.,Type checkType checks are used to check that the correct type of data has been entered in a field.For example if numeric data is being input a type check could be used to make sure that text data isnt entered by accident.Length checkLength checks are used to check that input data contains a certain number of characters.For example if a value in a certain field had to contain five digits and only four digits were input,an error message would be given to the user.,Presence checkA presence check is used to make sure that a value has actually been entered in a field.In some database files entering data in certain fields can be optional.Other fields,such as key fields for example,are compulsory and must have values entered in them.A presence check makes sure that data is present in a field where it is compulsory that a value is needed.,Parity checkSometimes when data is being transferred electronically from one place to another it can become corrupted.A parity check is used to make sure that data has not been corrupted during transmission.Data is transmitted as a binary pattern of 0s and 1s.A parity check involves adding an extra 0 or 1,called a parity bit,to the binary pattern so that the total number of 1s in the pattern is either an even number,this is called even parity,or an odd number,this is called odd parity.,In even parity the parity bit is set to either 0 or 1 so that the total number of 1s adds up to an even number.In this example there are four 1s so the value 0 is needed in the parity bit to keep the number of 1s even.,In odd parity the parity bit is set to either 0 or 1 so that the total number of 1s adds up to an odd number.In this example there are two 1s so the value 1 is needed in the parity bit to make the number of 1s odd.,Hash totalHash totals are used to check that groups of numbers have been input correctly.A hash total is the sum of a group of numbers that are going to be input.The hash total is input along with the numbers.The computer calculates a hash total for the numbers that have been input.If the hash total calculated by the computer does not match the hash total that was input with the numbers then one or more of the numbers have either not been entered or have been entered incorrectly.,Check digitCheck digits are used to validate long numbers that have a lot of digits in them.A check digit is an extra digit placed at the end of long number that can be used to check if the number has been input correctly.Check digits are often used to check numbers that have been input using direct data entry devices such as bar code scanners or light pens.,The value of a check digit is worked out by performing a calculation using the individual digits that make up a number.This calculation gives the value of the check digit which is then added as an extra digit to the end of the number.,Calculating check digits using the modulus-11 methodEach digit is assigned a weight starting at 2 with the right hand digit;Each digit is multiplied by its weight;The results of these calculations are added together to give a total;The total is divided by 11;The remainder is subtracted from 11 to give the check digit.The two exceptions are:If the remainder is 0 and the result is 11 the check digit is 0,not 11.If the remainder is 1 and the result is 10 the check digit is X,not 10.,Coding dataWhen data is input using a manual input device such as a keyboard,errors often occur due to values being entered incorrectly.A common mistake is to swap two letters or digits around;this is called a transposition error.One method that can be used to cut down on errors like this is to use coded values for data.Suppose that a field could contain one of three possible values;small,medium or large.Instead of typing in the full word each time we could instead type S,M or L.,The advantages of coding values are:Fewer key presses are needed when entering a value in the field so there is less chance of the wrong keys being pressed;Time is saved when entering data because there is less to type in each time;Database packages allow automatic validation checks to be set up to make sure that only the allowed codes