Computer notes olevel

Beaconhouse School SystemModel Town Boys Branch

SECTION 4Generic software and the organization of data The aim of this section is to acquaint the candidates with a broad view of generic software packages. It is expected that these will be experienced through practical work. Although candidates may choose to become expert in the use of a particular package, only a general knowledge is required of the kinds of features typical of generic packages.

4.1 Software for word-processing, database management, spreadsheets, graphics, communications, multimedia, data-logging, CAD programming, desktop publishing and web design

Candidates should appreciate ways, including import and export, of using programming, desktop publishing, word processing packages, spreadsheets, databases, graphics packages, information retrieval packages, and show an understanding of the use of graphical user interfaces, communications software (including email), web browsers and search engines and authoring packages. They should appreciate the virtues and disadvantages of integrated packages, and of generic packages compared with specially written software and how packages may be customized by the use of macros. They should be able to explain the use of the tools associated with data-logging.

How applications packages solve sets of standard problems. Typical problems capable of solution by packages. Use of standard techniques or routines for established forms of processing (for example, file processing, sorting, simulation)4.2 DataCandidates should be aware of the standard methods of data collection, verification and validation, and where it is appropriate to use particular methods. Candidates should understand that data, particularly data held in files, requires access in different ways depending on the particular application. The medium on which the data is stored, and particularly the way in which it is organized, depend on the requirements for access. Candidates should be familiar with the idea of file ordering and the principles of sorting and merging. They should have experience of sequential file processing and of processing individual records by means of record keys.The relationship between information and data; the collection of data; methods of ensuring its correctness (including validation and verification and the distinction between these); the coding of data for input; the presentation of useful information from processed data; analogue-to-digital and digital-to-analogue conversions

Candidates should be able to describe and select methods of automatic data capture in a number of applications. Candidates should be able to describe methods of data collection, verification, validation and presentation, and give examples of analogue-to-digital and digital-to-analogue conversion. Candidates should be able to select and justify appropriate methods of data collection, verification, validation and presentation, and assess the use of physical variables such as temperature and pressure to control processing activities.

File organization: different forms of organization, depending on the data stored and the requirements for processing; processing methods

Candidates should be able to describe the need for and the simple processing of files and select with reasons appropriate file organization and processing methods for a particular application, and understand routines used for file maintenance such as updates, insertions and deletions.

Data types: numbers, characters, strings, arrays, the need for different data types and structures to represent the

Candidates should be able to identify the different forms of data and representations for processing which relate to a given simple problem, and explain the need for different data types and

Muhammad AzizullahIT Teacher


data of problems which are being solved using a computer

structures and how these relate to the data of a given problem.

SECTION 5Hardware, systems and communications The aim of this section is to draw together the experience of various kinds of hardware and types of processing, and to examine the concepts of operating systems and communications.5.1 Hardware Computer, microcomputer, microprocessor, standard input and output devices, broad classes of processor power;

Candidates should be able to identify the use of laptop computers (differences to desk top PCs); the use of CCTV; the use of microprocessors in everyday objects such as cameras, digital watches, etc. Candidates should be able to describe suitable input and output devices in relation to the requirements of applications and the use of specialist input and output devices (e.g. to help disabled people, devices to communicate with virtual reality systems, etc.).

The functions and characteristics of storage media;

The functions and characteristics of storage media such as RAM, ROM, CD-ROM, CD-R/W, DVD, USB flash memory, disks and tapes need to be considered in relation to the requirements for applications.

The characteristics and performance of a range of peripherals (including control and communication devices).

Candidates should be able to discuss the suitability of different peripherals for various applications.

Software for word-processing, database management, spreadsheets, graphics, communications, multimedia, data-logging, CAD programming, desktop publishing and web design

Word ProcessingMeans using IT to produce text such as letters and reportsA piece of text produced by a word processor is called document

AdvantagesEasy to correct MistakesResults are easy to read & look professionalTest can be stored and can be reused another timeA word processor can be set so that text moves along as you insert charactersSpelling and Grammar can be checked automaticallyWhen line finishes cursor automatically goes to next line (Word Wrap)

RequirementsA Word Processor ProgramA disk unit to store the Documents, Floppy may be used as backupA quality Screen



A quality Printer

Entering editing and improving TextBy typing a text into a word processor documents is created, by entering ENTER user can make paragraph. It is not necessary that user can enter at the end of each line because cursor automatically goes to next line. This process is known as word wrapping

Editing TextIf user makes mistakes or wants to change anything then user can move by using arrow keys. Two ways most word processor allow to change

1. OVERTYPE as you type you rub the character our cursor is on2. INSERT the letters you type are inserted and all the rest of the test moves to

make room for that

Appearance and Styles1. Underline Text

This line has been double underlined2. Bold Text

This line is in bold letters3. Centering

This line has been centered4. Italics

This line is in italics5. Double Line Spacing a blank line is left after each line.

NOTE: Above mentioned Activities can be perform by going into the Format menu then click on font

FONTSMany word processors offer a choice of fonts, i.e. character design. A font is a set

of printed characters of a particular size, style and design.Examples of fonts

Arial BlackArialTimes New RomanImpactMonotype Corsica

SPELLINGSA spell checker is a program which checks the spellings of words you have used against those in a dictionary. A dictionary is a file of



word stored with the spell checker. Nouns are not found in the dictionary. If the word is not found, the spell checker stops for you to decide what to do. Some times it gives you several options to select the appropriate one.

AUTO CORRECTAuto correct feature allows you to correct the most common mistakes

itself. Like of you type “hte “it will automatically correct it into

“The”.You type Result

(r) ®(tm) ™:)

Note: User can add most common word used like Beaconhouse will give error you can add to dictionary so next time when ever user use this word it will not give an spelling error

TABS, MARGINS & INDENTSWhen a TAB key is pressed, the cursor jumps across the page several positions at a time, the normal Tab position are usually about 5 Characters widths apart.To start the first line of each paragraph 5 spaces in form the edge of the page. The TAB key helps to always move the first line the same distance.The MARGINS are the limits which have been set for text near the edges of the page. They can be changed so that the text is nearer the edge or further away form itThe INDENT is the distance text is moved in from the margin. You can indent part of the text without moving the actual marginTo JUSTIFY the text means to keep the letters in a straight line at the edge of the page.

Note: if the text is justify at both the left and right the word processor has to put extra spaces in between the words to keep the ends of the lines straight.

WORKING WITH BLOCK OF TEXTWord processor allows you to mar a block of text. You can then

1. Delete the whole block 2. Make a copy of the block of text somewhere else.3. Move the block somewhere else without making a copy

SEARCH & REPLACE



Search for a word or words (sometimes this is called ‘find’). You simply key in the word and the cursor moves to the first place it occurs in the document.The computer replaces one word by another one, wherever it finds it. Usually you have the choice of deciding whether to replace it or not when it is found.

MAIL MERGEMany word processors can produce a set of letters by adding to them the name and address of each person on a mailing listA standard letter is a letter which an organization stores ion file because it is used frequentlyA personalized letter is a standard letter which is made to look a personal letter by adding the recipient’s name, address and possibly other detailsA mail merge is the operation of producing a set of personalized letters by merging the personal details with the standards letterThree steps are needed to carry out the mail merge

1. A file of names and address2. The standard letter with gaps3. The instruction how to merge them these may be codes within the standard letter.

Advantage of mail merge a mail merge allows an organization to produce a large number of letters quickly and cheaply.Disadvantage of mail merge a mail merge sometimes makes it too easy to produce letters which people do not want. They may be regarded as ‘junk mail’.

Desktop publishingFor the production of leaflets, newsletters, magazines, etc. the facilities offered by a word processor are not sufficient. A desktop publishing package is required.Desktop Publishing (DTP) is the use of computer system to produce page layouts of high enough quality for printing or publishing FEATURES

1. Option within the package to produce text and graphics2. Ability to import text and graphics from other packages3. Ability to divide page into columns4. Facility for moving pictures and pieces of text on the page and adjusting their size

to fit spaces.5. Guides to position text and graphics accurately.6. A wide range of fonts, sizes and styles of text.7. Flowing of text around objects and from page to page.

REQUIREMENTS1. A 2. DTP Program3. A high Resolution Monitor

4. A mouse5. A Laser printer

Also Recommended1. A word processor to prepare quantities of text before importing them into the

DTP package.



2. Various Specialist graphics packages for preparation of graphics which could not be produced using the limited drawing capabilities of the DTP package.

3. A library of clip art is a set of standard graphic design which can be imported into the work.

4. A scanner to copy pictures as another source of graphics.



Database ProgramsInformation retrieval means obtaining information you have specific from s set of stored data. The stored data is usually a data file or a database.

The word database is used with three slightly different meaning1. A large set of data containing all the information important to an organization.

This is an organizational database.2. A program for handling files and retrieving information from them. This is a

database program.3. A file created by a database file program. This is a database file. (a group of

related data files is called database )

WHEN TO USE DATABASESearching through a file and producing lists of records which fir certain conditions;Sorting a file into a different orderProducing statistics about the data in a file such as average height, etc.

PLANNING HOW TO DESIGN A DATABASE1. Decide what data is required for the problem you are solving;2. Think of a name for your data file.3. Plan your fields you are going to have4. Decide on a key field or a sort field5. Plan how to collect and record the data before it is typed in

Deciding what data you require1. Is the data in the best form for solving the problem? For example. If the data

comes from asking people questions do you wantYES/NO answers

ORTo give people a choice of several possibilities so that the data is 1, 2 or 3.

ORTo let them write an answer in full

2. Are you trying to put in too much data- or too little? You do not want to collect and type in data you are not going to use BUT it may be difficult to add another field later if you find you really needs it.

3. Do you need to use codes for some of the data? For example, if one of your fields is Gender (SEX) it is better type just M or F rather than MALE or FEMALE

Name for your DATA FILEChoose a name which will remain you what the data is e.g. if the data is from the 1991 census that name the file CENSUS91. Do not call it BLUEGUM91 even if it is the sixth file you have created.

Planning what fields you are going to haveGive the field nameWhat type of data the field contains (Numeric, data, alphanumeric)How much space it will take up i.e. surname could be given 20 characters as this is the longest a surname is likely to be.



FIELD TYPESMost database allowAlphanumeric = anything you can type from the keyboard. Address Name & WordsNumeric = this can be any numberDate = default form is day/month/yearSome database allowInteger = any whole Number, Positive or negativeLogical = these can have the value TRUE or FALSELabel = so that you can put extra information on the screen

Deciding on a key field or sort Often a database package will ask you for a sort field or a key field. This is so that your data dose not has to be stored in the order in which you typed it. Instead it can be stored in an order which is useful.All you have to do is decide on a field which results in the file being in an order which is helpful when looking at it.

Planning how to capture the data.Before you can enter any data into a database you have to capture it.You will have to obtain the data from somewhere e.g.

By Asking people questionsBy looking things up in booksBy doing an experiment

You or someone else will have to write it down.

Database FILE BEACONHOSUE 9CC CLUB MEMBERSHIP

Memb. # First Name Surname Age Sex (M/F) PhoneType (Numeric)

Type (Word) Type (Word) Type (Numeric)

Type (Word) Type (Numeric)

Width (6) Width (25) Width(20 Width (2) Width (1) Width (8)KEY FIELDSORTED

Form Format (Manual)


BEACONHOSUE 9CC CLUB MEMBERSHIPMembership Number ___________First Name ___________________ Surname _______________________Age at 1/1/2010 __________ Years Sex (M or F) ____________________Address ______________________ Phone ___________________________________________________________________________________


CREATING A DATABASE FILEMain steps in creating a database file are

1. Produce a form to collect your data on, this can be done on a word processor2. Collect and record the data to be keyed in3. Run the database program4. Name the database file5. Key in for each field its name, type and possibly its length.6. Choose a sort field7. Enter the data into the database , one record at a time8. Save the database

Editing database filesMost database allow you to alter

The fields in your database. You should be able to add fields and delete fields. You should also be able to change the name and length of fields and the type of data. You have to careful, though, as you may lose some data in the process.

SEARCHING AND QUERIESYou can tell a database program to look for all the records in your database files which agree with certain conditions. This is called searching.A query (or search string) is the set of conditions you set for the computer to check the records against. A match happens when the computer finds a record which agrees with the query set.

Query ConditionsUsually you set a query and then tell the program to search. It produces a list of all the records which match the query.A query can include comparison operators which use any of the following to check for a match.= are they equal?

< is the first less then second?

> is the first greater than second?

<> Not equal

<= Less than or equal

>= Greater than or equalThe following data has been collected

First Name Surname Date_ of_Birth HeightJohn Smith 10/03/78 182Janet Smith 12/11/79 170Bernard Toms 01/09/77 180Tracey Hinds 23/02/79 176David Walker 19/02/78 189Petra Chaffey 21/08/79 178



1. The Query Surname = ‘Smith’ would given matchesJohn Smith 10/03/78 182Janet Smith 12/11/79 170

2. The Query Height > 180 would give:John Smith 10/03/78 182David Walker 19/02/78 189

Harder QueriesThe world logical applied to a statement or an expression means it is either TRUE or FALSE

1. NOT to invert a logical expression2. ‘Multiple queries’ using AND or OR between Logical expressions;3. Queries to check whether one string of character is contained in another, i.e.

whether one string is a sub-string of anotherExample of logical statement

‘Cows can fly’ is a logical statement which is FALSEExample of logical expression

‘A=6’ is a logical expression. (If A is 3 the expression is FALSE; if A is 6 it is TRUE)Notes:There is no set way of writing queries. Different database packages have different methods.

1. In some packages a string has to be enclosed between quotes instead of apostrophes, e.g.“Smith” rather than ‘Smith’

2. Sometimes the words AND, NOT, OR are replaced by symbols or have to be between full stops, e.g.

Surname = ‘smith’ AND Forename = ‘John’Could be

Surname = ‘smith’ .AND. Forename = ‘John’Or it could be

Surname = ‘Smith’ & Forename = ‘John’3. Your database probably has a special query for ‘contains’4. Most databases do not allow the query

EYES = ‘Blue’ or ‘Green’You have to say

EYES = ‘Blue’ or EYES = ‘Green’5. Be careful about Capital Letters

The query EYES = ‘Blue’ might give a different match fromEYES = ‘BLUE’ orEYES = ‘blue’

STATISTICS AND SORTS

SORTS A database will usually allow a file to be sorted into ascending or descending order for one or more chosen fields. If two sort’s fields are chosen, then the second one will only be used if two records have the same value in the first sort field.



Statistics your database program will usually do calculations for you. These can be done EITHER

On all the records in the databaseOR

On just those records which have been selected by a query.

The statistics would operate on one of the numeric fields in your file. Examples are SUM or total produced by adding up the value in that field for every record. Average the average for all the values in that field Maximum or highest the largest value in that field Minimum or least the smallest value in that field Count the number of records selected

MORE ABOUT DATABASEGenerating a report A database report is a set of results from work on a database put together as a document for printingInstead of having to print out your results as you produce them, most database program allows you to produce a report. You then print this out at the end, when you have finished. A report may include.

1. List of records produced as the result of searches through your file;2. List of records sorted into a different order from the original file;3. Statistics Calculations carried out on the data in the file;4. Text added by the user to link the results in the report and make it possible. It may

allow underlining, different fonts, page numbering, etc.

Advantages of database reportIt allows results to be printed out together as one documentIt allows text to be added to link results together

Note: if your database dose not has a facility then export each result to a word processor file and produce a report using the word processor

A Query languageA query language is the set of words and symbols which are used to retrieve information

Note:1. Often a query language enable a user to retrieve information interactively2. In the simplest case the language consist of single query statement

ExampleList Forename, Surname, Height FOR Height >= 180 .AND. Height <=186

This will list the followJohn Smith 182Bernard Toms 180



A more complex language will allow the user to put instructions together in a sequence. This may be done by.EITHER

Writing the sequence in the form of a programOR

Producing a Macro

Example@ 1,5 say “ Maximum Height acceptable:”@ 1,39 Get Max@ 3,5 Say “ Minimum Height acceptable:”@ 3,39 Get MinReadList Forename, Surname, Height FOR HEIGHT >= Min .AND. Height <=MaxWait

Above mention example is in language which accompanies the database package dBaseThe program shown asks the user to type in values for MAX and MIN. It then displays the Forename, Surname and height for all the records with heights from Max to Min inclusive. The result might be as follow

Maximum Height acceptable: 186Minimum Height Acceptable: 180

John Smith 182Bernard Toms 180

Say causes text to be printed on the screen. Get causes the computer to expect input. The numbers after the @ symbol give the position on the screen where this will happen

Advantage of Query Language1. It allows user to retrieve information from a database without having to write a

complicated program.2. If the query language allows the user to store a sequence of instructions then:

The sequence can be used again Variable can be introduced. These enable the user to use the same sequence of

instructions to retrieve different sets of data, e.g. in the example above MAX and MIN are variables to which the user can give values

LINKED FILESOften an organization has a number of files which have data in common.

Database programs often allow the user to link files. Usually two files are linked by telling the program that one field in the first file is the same as a field in the second file.



Spread Sheets ProgramsIf you want to use a computer to model a situation involving numeric data, then a spreadsheet is often the simplest way to do it. (Simulations and expert systems require a lot of knowledge and time to produce.)A SPREADSHEET program gives you a table on the screen in which you can move around and in which you can place data.

The Table consists of rectangular slots called cells. The cells are arranged in rows across the page and columns down the page.

Labeling CellsThe user can refer to any cell or group of cells by using a label. Usually a label for a cell consists of the column followed by the row. Different programs have different ways of labeling the row and columns. This label is called a reference.Entering dataThe data is placed in the cells can be

Numbers Words and other text Formula which make it possible to do calculations on the numbers.

Data is usually entered by moving to the cell you

want using the cursor keys or the mouse and then keying it in.



Example of a simple spreadsheetShop Sale Spread Sheet

Beaconhouse school shop is run by the teachers and pupils and is open in break times and in the lunch hour... It sells anything useful which cannot be supplied free by the school.This includes pen and pencils, floppy discs for computers, T-shirts, etc. The pupils who help to run it learn as they work and they record a summary of each week’s takings on a spreadsheet. This gives a summary of the sales for the week. The columns shows;Day - the day of the weekI.C. - the person In charge for that day;Sale. - the number of items sold;Cost - the cost to the shop of that items which were sold;Income- the amount of money taken for the day.Overhead- Administration cost to the Items

Note: The text in each of the cells B2 and A6 is too long for the cell. In the case of B1 the spreadsheet has let the text overflow out of the right of the cell. For cell A7 however, the ‘y’ of Wednesday has been cut off because there is something in B7. One solution to this to widen column A.

IMPROVING THE LOOK OF A SPREADSHEET.You should be able to improve a spreadsheet as follow.

Changing the column widths. You can make the column wider or narrow.

Underline and bold.Many Packages will allow you to use underlining, bold and often to change fonts. Underlining is useful to;

Emphasis heading Put a line under a column of figures which is being totalled

Centering and justifyingMost spreadsheets put test at the left of a cell and numbers at the right. However, if you want to you can change this so that data is at the left, the right or in the center of the cell.



The spread sheet will probably allow you to do this to columns or rows or whole blocks of cell.

Changing the formats of numbersA spreadsheet will allow you to change the formats of numbers;To make them amounts of money or percentages;To change the number of decimal placesNote: Entering amounts of money.

If you type a £ sign the spreadsheet will take you type as a string instead of an amount of money. The amount should be entered as an ordinary number. The format can be changed to pounds later.

FORMULAThe contents of a cell can be text or a number but they can also be a formula. It is the formula which allows spreadsheet to do calculations and to model real situations.A formula is a mathematical expression which allows the value in one cell to be worked out from the values in other cells.

Note: There are different ways of letting the spreadsheet know that the contents of a cell are a formula. Often this is done by starting the formula with an ‘=’ sign.

Example: of a simple formula.A spreadsheet has the following data in it;

1. Cell C2 contains 11, cellD2 contains 2.5;2. The formula = C2 + D2 is put in E2

When the ENTER (or RETURN) key is pressed the value 13.5 appearsNote: The cell E2 contains the formula = C2+D2 but what you see in it is the result.

Example of formula.The Beaconhouse School Shop Sale spreadsheetFollowing Figure shows the original spreadsheet improved by changing the money formats and adding simple formula as follow



In C10 a formula for the total sales which adds the five cells above it:=C5 + C6 + C7 + C8 + C9

In D10 a similar formula for the total cost:=D5 + D6 + D7 + D8 + D9

And in E10 a similar formula for the total income:=E5 + E6 + E7 + E8 + E9

RANGE IF CELLSA range of cells is a group of cells referred to as a unit.On many Spreadsheets a range of cells is referred to using a colon (:).

Example range of Cells1. C5:C16 is all the cells in the column C between C5 and C16 inclusive. Including

C5 and C16 this covers 12 cells.2. C2:D3 is block of cells C2, C3, D2, D3.

FUNCTIONSOn most spreadsheets the user can include mathematical functions in a formula.Examples of Functions:

1. SUM: The result of adding the numbers in the cells given.2. AVERAGE: The average of the numbers in the cells given.3. COUNT: The Number of the cells in the range given.4. MAXIMUM: The largest value in the cells given.5. MINIMUM: The smallest value in the cells given.6. More complex mathematical functions such as SINE, COSINE, etc.

Different spreadsheets will have different ways of doing these and the words may be abbreviated e.g. AVG for Average, MAX for Maximum.

Example of function in useBeaconhouse school shop spreadsheetThe formula in cells C10, D10, E10 calculate the totals of sales, cost and income. To do this they use the SUM function.The formula used to produce the totals in the following figure can be replaced by:



In C10 - =SUM(C5:C9)In D10 - =SUM(D5:D9)In E10 - =SUM(E5:E9)In the following figure averages for the sales, Cost and income totals have been calculated using:In C11 - =AVG(C5:C9)In D11 - =AVG(D5:D9)In E11 - =AVG(E5:E9)

COPYING CELLSOne of the most powerful features of a spreadsheet is its ability to copy data and formula.Example of copying formulaBeaconhouse school shop spreadsheetThe pupils who run the Beaconhouse school shop are very keen to know their profits.They add columns into the SHOP SALES spreadsheet for profit and Profit%:

Profit is worked out by subtracting the cost from the income Profit % is worked out by dividing the profit by the cost and then expressing it as

a percentage.The spreadsheet’s COPY CELLS option is then used to copy the formula into other cells.



In the figure bellow the previous SHOP SALES spreadsheet has been improved as follows:1. Only two formulas were actually typed in. these were:

In cell G5: = E5 – D5 and In cell H5: = F5 / D5

2. The other profits and percentages were produced by copying formula down the columns:

Copy cell G5 down the range G6:G11 and Copy H5 down the range H6:H10 (the value in G10 is overall percentage

profit.)3. The columns were then tidied up:

The numbers in column F were reformatted by marketing them as a block and making them into amounts of moneyIn the same way the numbers in column G were reformatted to be percentages and to have only two places of decimals.

Note: The spread sheet has not copied the formula exactly, the formula = E5-D5 has been changed to E6–D6 and then E7-D7, etc. as we go down. As it happened this was just what was needed in this case. Most spreadsheets allow for formula to change as they re copied, or to stay the same, as the user requires.

A REFERENCE means the label given to a cell in a formula, e.g. C5, G6.A RELATIVE REFERENCE is a label which changes when the formula is changedAn ABSOLUTE REFERENCE is a label which dose not change when the formula is copied



Examples of absolute reference and relative referenceIn many spreadsheets an absolute reference is formed by adding a $ sign.

$C$5 is an absolute reference and will not be changed by copying C5 is a relative reference and will change when it is copied In the case of C$5, the C can Change but the 5 cannot

Example of an absolute referenceBeaconhouse school shop spreadsheet

The Beaconhouse school shop gives a percentage of its profits to charity. This percentage is changed from time to time but at the moment it is 20%

1. Column I has been reserved for the donations to charity2. In the following figure the percentage (20%) has been put in cell I2.3. Each day’s donation is then worked out by multiplying the profit for the day by

the contents of I24. The formula for I5 is =I$2*G5



Note :1. The $ sign has been used to make the number 2 an absolute reference so that it

dose not change when the formula is copied down column I2. In most computer packages an asterisk (*) is used as a multiplication sign

A SPREADSHEED AS A MODELA spreadsheet is a model of the situation it represents.

1. The behavior of the model copies the actual situation. If the data produced in the actual situation changes then the spreadsheet can be changed to show this.

2. The behavior of the model is determined by the set of rules. In the spreadsheet these rules are produced by formula.

3. The model can be studied to forecast what will happen in the real world. You can try putting values into the spreadsheet just to see what will happen. The formula will make other values change.

Example of changing a spreadsheet to see what will happen Beaconhouse school shop spreadsheetThe pupils who run the Beaconhouse school shop want to increase the amount given to charity. They try various values for the charity percentage to see what will happen

A value of 25% increases all the daily donations and increases the total donation for that week to £6.27.



Graphics and charts ProgramsGRAPHICSThe term computer GRAPHICS refers to any picture or graphs produced using a computer.Examples of computer Graphics

1. The computer- produced landscape in s simulation game2. A mathematically generated pattern3. Business Graphics- graphs and charts produced to show results in an easily

understood way.4. Computer aided design (CAD) graphics- designs produced by interacting with a

computer and drawing on the screen.DRAWING AND DESIGN PACKAGESPrograms which allow you to produce pictures include packages which allow:

1. Freehand drawing and ‘painting’This is usually done with a ‘paint’ package which allows lines to be drawn freehand with ‘pens’ and ‘brushes’

2. Computer Aided Design (CAD)Accurate drawings are produced with a sophisticated CAD package.

3. Image manipulationImage produced by scanning, using a digital camera, or by using a drawing package are improved and changed

4. 3-D modelingPictures are built up from their coordinates using triangles or polygons. They are given a 3-D appearance by mathematical operations to produce the appearance of shadows and highlights

5. AnimationA number of gradually changing images are produced to give the appearance of movement. Techniques include morphing where the computer calculates the intermediate image to make one image appear to change smoothly into another

STORAGE OF PICTURES

Pictures are stored in a computer in two different waysA PIXEL BASED package stores a picture as a set of dots. This is also known as BIT-MAPPED.An OBJECT BASED package stores each picture as a set of shapes, storing the coordinates of each shape. This is called VECTOR BASED or LINED BASED.Note:An enlargement of an object based drawing is more accurate than a pixel based one. This is because when you enlarge a pixel based picture you see the pixels and it appears as a set of squares

PAINT PACKAGE

Paint package is a general term for any program which allows freehand drawing and coloring.



CHARACTERISTICS OF PAINT PACKAGE Drawing is done on the screen using a mouse. Storage of the picture is in pixel based form. A ‘zoom’ facility allows you to

enlarge part of the picture and change individual pixels. Selections are made from various icons and menus around the edges of the screen.

Options usually include.o Different thicknesses of pen or brusho Different ways the pen or brush can draw – in blobs or stipple or lines;o Colors- the set of colors which you select from is called a palette;o Patterns- you can usually fill shapes with a pattern as well as with plain

colors.o A rubber for rubbing out mistakeso Standard shapes you can draw- Such as oval, circle, square, rectangle,

curve;o Some scissors or a net- something you can mark an area of the picture

with.When you have done this you cab usually:

i. Delete that part of the picture ORii. Move it to somewhere else OR

iii. Make a copy of it.o Limited ability to key text.



Picture produced using a paint package. The set of shapes were used- a curve for eye brow’s the frame was drawn using thick lines and curve shapes. The ‘zoom’ facility was used to get the details right

Advantages of pixel based paint packages1. Drawing can be done freehand2. Small areas of the drawing can be improved by zooming and retouching.3. Operations such as copying and erasing can be done on parts of shapes.4. Use can be made of scanned pictures.

Disadvantages of pixel based paint packages1. Stored pictures take up a great deal of memory2. Enlarge image have ragged outline.

CAD GRAPHICSA COMPUTER AIDED DESIGN (CAD) system allows the user to accurate drawings. It is also known as computer aided draughting.CHARACTERISTICS OF CAD SYSTEMS

1. Usually object based, i.e. Storing lines and shapes rather than pixels.2. Aids to accurate positioning and drawing

A grid of guide lines An accurate measuring system on the screen.

3. Powerful facility for changing drawings, e.g. scaling, rotation and reflection.4. Libraries of standard components, e.g. kitchen furniture and appliances, electronic

components5. Software to do calculations from the drawing, e.g. calculation of length and area,

calculating the cost of standard components used in a design.6. Specialized computing equipment.



HARDWARE OF CADA cad system is demanding for processing, input, output, storage.ProcessingCAD requires fast processing. Operations like scaling and rotation require a mathematical operation to be carried out on every object in the drawing. How ever the most powerful microcomputers are quite adequate for this.Inputa mouse is not really adequate as an input device. A graphics tablet can be used with a punk or a stylus:

for selection of shapes and options from a template; for accurate digitizing of existing drawing.

Output A high resolution monitor is required for close work. A plotter or at least a laser printer is needed for hard copies.

StorageStorage is required for

1. DrawingWith an object based system a simple drawing uses very little store. How ever, for practical applications drawing are complicated and required a large amount of storage.

2. CAD softwareProfessional CAD programs are large and complex.

3. Component databaseA CAD system requires large amounts of

o Hard disko Ram in the main store

SOFTWARE FACILITY ON CAD SYSTEMS1. Grid Lines- a set of horizontal and vertical lines which help to place objects

accurately: The distance between the grid lines can be changed to fit the scale of the

drawing The program can be set to ‘snap’ to the grid lines. This allows objects and

points to be positioned accurately2. Scaling- The whole drawing or objects in it can be made larger or smaller.

Usually you have to: Select the object or objects to be scaled Choose a scale factor Choose a point from which the object are scaled

3. Rotation-A part of the drawing can be rotated about a point on the screen. Usually you have to

Select the object to be rotated Select a point as a centre for the rotation Indicate how far round to rotate the object- Usually with the mouse.



4. Reflection - an object is reflected by using a line as an imaginary mirror. Each part of the object is copied to be the same distance from the mirror but on the other side of it. The effect is to turn the object round to face the other way

Advantages of CAD Systems1. Wider range of operations than a simple paint package2. More accurate drawing. CAD package re object based:

a. Drawing can be enlarged without losing detailb. Accuracy is possible without using too much storage.

3. Wide range of standard shapes available4. Calculations can be done from drawings.

Disadvantages of CAD Systems1. Professional CAD software is expensive2. CAD requires high quality input, output and storage

CAD/CAM

CAM is computer aided manufacture. A machine tool such as a lathe is controlled by a computer which sends it instructions to select tools and to use them to make metal components.CAD/CAM is a computer aided design/ computer sided manufacture, in which a CAD system and a CAM system are integrated.In CAD/CAM , data from the CAD system is converted to a set of instructions for the processor controlling the CAM equipment. Once a part has been designed using the CAD software the other processor automatic

1. Conversion of the data into a set of machine tool instructions2. Operation of the CAM systems

Selection of Tools (Cutters and Drills) Selection of Speed (for a drill or a lathe) Movement of the tool machine the part being manufactured

GRAPHS and CHARTSBusiness graphicsGraphs and charts are often referred to as ‘business graphics’. They are usually produced by using

1. A Special Business Graphic packageOR

2. The chart option on a spreadsheet packageOR

3. A graphics option in an integrated package

Usually the data for the graph or chart comes from rows or columns of a spreadsheet by1. ‘Cut’ or ‘Copy’ from the spreadsheet and ‘Paste’ into the chart

OR


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2. Exporting the data from the spreadsheet as a file and importing it into a chart package

Information required to Produce a GraphTo Produce a clear graph you need.

1. Data This may be referred to by the chart package as ‘Data’ or ‘Series’ or’

Values’ It is usually obtained from the rows or columns of a spreadsheet.

2. Title of the Graph A main title to state what the graph is e.g. Annual sale Report A subtitle to give more detail to the title, e.g. Average Monthly Sale for

20103. Title for the axes (Except on pie charts)

These explain what the axes represent, e.g. on the vertical axis: Monthly Sale Figure, on the horizontal axes: Months

4. Labels on the axesLabel to tell you the size of the value shown on the graph, e.g. on the vertical axis: 10, 20, 30 etc on the horizontal axis: Jan, Feb etc

5. A legendAny information added to a chart or graph other than on the axes is often called a legend. For example if there are two temperature graphs on the same chart, one with squares and one with circle, the legend might be

--o-- Maximum --■—Minimum

1. Many Chart packages refer to the vertical axis as the y-axis and the horizontal axis as the x-axis.

2. Often the package works out the scales for the axes automatically.

TYPES OF CHARTSA bar chart is made up of rectangular blocks of bars. The length or height of a bar shows the size of the number it represents.



A pie chart is in the form of a circle with lines drawn out from the centre. It looks like a pie which has been cut into uneven slices. Each slice represents a number- the bigger the slice, the bigger the number. A pie chart shows what each of the values is as a fraction or a percentage of the total.A line graph has a set of points joined by a lineA scatter graph is produced when two different quantities are plotted against one another to find out if they are related in some way. The scatter graph simply consists of a set of points.


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WHICH TYPE OF CHART TO USE

Bar ChartUsed to show the relative sizes of a set of separate values. for example, a graph to show the amount of support for each political party at one election.

Line GraphUsed to show how a quantity is changing. Often the horizontal axis represents a time scale. For example, a graph to show how support for the different political parties has changed over the past ten years.

Pie ChartUsed to show how something is shared. For Example, a graph to show the numbers of votes for each political party as a percentage of the whole electorate.

Scatter GraphUsed to show how two different quantities are related. For example, a graph of unemployment numbers against



crime numbers of different towns to see if there is a connection between crime and unemployment.



COMMUNICATIONSGenerally COMMUNICATION means sending information between one person or device and another.The term DATA COMMUNICATION is used particularly when the data being send between a user and a computer or between computers.TELECOMMUNICATIONS are data communications over large distances

Example of communications1. Two people speaking on the telephone2. A sale department sending a fax to a customer3. Using a modem and a terminal to contact a remote computer

Type of communicationsSimplex: One can send other can receive only .One way communication Like TV,

Radio.Half Duplex: One can send other can receive then other can send first one can receive.

One at a time like in wireless system one can speak other can listen only. Full Duplex Both can communicate at same time like Phone.

VideotexVideotex is a term for any information system which uses a computer to transmit data to uses’ screens.Teletext and viewdata are both examples of videotext.Teletext is s system for sending out information using ordinary television signals. The customer has an adapted television set and the information is displayed as pages of text. The user can receive data but cannot send it back.Viewdata is an interactive information system where the telephone is used to link users to the host computer. Normally the user has a modem used with a terminal or a microcomputer. The user can send message back to the computer.A page is one screenful of information and is send as a unit. For some viewdata systems, the user has to pay for each page which is viewed.

FAXFax (short for facsimile) is a widely- used method of transmitting the contents of documents using ordinary telephone lines.The fax machine at once end scan the document and converts the image into telephone signals (analog). The fax machines at the receiving end uses these signals to reproduce a copy of the document. The document send can include both pictures and text.Advantages of FAX

1. High speed compared with letters2. Convenience and simplicity – a mixture of written messages and prepared

information can be sent with no more trouble than making a phone call.Disadvantages of FAXFaxed printouts are sometimes of poor qualityIt is relatively difficult to computerized faxed information



Note: Normally a computer is not involved in fax transmission. However, it is now possible to buy a fax modem and suitable software to transmit and receive computer information via fax



TELETEXTExamples of teletext systems

1. The BBC system- Called CEEFAX. This appears in full on BBC2, with a shorter, fast access version on BBC1.

2. The ITV system – called TELETEXT, Part of the information for this appears on ITV and part on channel 4.

3. Similar systems on satellite channelsCharacteristics of teletext systems

1. Teletext can only be viewed on specially adapted televisions.2. Teletext systems are not interactive. The user cannot send messages back to the

computer3. For a given television channel, the same pages are sent out repeatedly one after

another. All the user can do is to select which page to look at and wait for it to arrive.

4. The user has a keypad (usually remote and hand-held) and keys in the numbers of selected pages.

Hardware requirements for teletext1. A television set adapted to receive the data.2. A remote keypad which includes buttons for teletext operations.

Examples of information available form teletext systems1. Up to date news2. Latest sports results3. Weather Information4. Detail of radio and TV programs5. Stock exchange prices

Application of Teletext1. Use of sub-title by deaf people

The teletext systems supply a number of services to deaf people including subtitles on many programs. As people on a program are talking, what they are saying appears in large letters in a rectangular box near the bottom of the screen. The user:


Computer System

Transmitter

Adapted TV


1. Select the channel showing the program2. Selects teletext3. Selects the subtitle page

2. Contributions from viewersBoth CEEFAX and TELETEXT run teletext pages written by contributes. Users can send items of news, reviews, stories and others items and these are included in the special magazine pages

Advantages of teletext: 1. It is relatively easy to select the information you want.2. The equipment required is fairly inexpensive3. Once you have the equipment, using it cost nothing extra4. Teletext data can be added to ordinary televisions pictures, e.g. subtitles, added to

programs for deaf people.5. Pages can be changed easily so information is up to date

Disadvantages of teletext: 1. There are only a limited number of pages to look at.2. The user cannot interact with the computer.

NETWORKS

A local area network (LAN) is a network which is all on one site, such as a school or block of offices. The work stations in a local area network are usually connected directly by cables.A Wide Area network (WAN) is a network which connects large numbers of computers and terminals over long distance. The work stations in a wide area network are connected by telephone or similar data links.Examples of NetworkLocal Area network

An interconnected set of computers in a net café.A network of computers in a school.

Wide are NetworksA public viewdata network such as campusA chain of banks with terminals connected to the bank’s headquarters.

MEANS OF COMMUNICATIONSData can be transmitted by:

1. Wire cableThis conducts data as electrical signals and may be :

a. Co-axial cable with only one wire in the middle for sending and receiving data;

b. Parallel cable which has a number of wires and allow several signals to be sent at the same time.

c. Standard telephone lines2. Fiber Optic Cable (also known as optical fiber cable)



This contains glass fibers and data is transmitted as light signals. It can transmitted for more data then wire cables but is expensive and not so flexible.

3. Transmitted signals without cables.Radio waves – including the use of satellitesMicrowave - very useful over relatively short distances.



Communications hardwareCommunication to wide area networks is usually achieved using a terminal and a modem with a telephone lineA modem (Modulator- Demodulator) is a device which allows a computer or terminal to use the telephone line for communication.

Example of use of Modem:If a terminal user is using a modem to access a public network the modem:

1. Converts digital signals form the terminal into analog signals and send them along the telephone line to the host computer.

2. Receives analog signals from the telephone line and converts them back digital signals for the terminal.

Characteristics of local area networks1. The workstations are normally microcomputers.2. The communication between workstations is usually along cables.3. The network contains peripherals such as hard disc units and printers to which all

users have access via the network.4. To use a program, the user loads it into his/her own workstations and runs it there.

This contrasts with many wide area networks where the user has only a terminal and all the programs run in a central ‘host’ computer

5. The network has special computers called servers to control the main disc units and printers

A print server is a computer on network which controls a printer.A file server is a computer on a network dedicated to controlling a hard disk and handling users’ files.

Note: the file server deals with the security of the file it controls. This includes checking passwords and user identities.

Advantages of Local area network.1. The stations can share peripherals. Disc units and printers can be of better quality

because they do not have to be bought for each station.2. Users do not need to use floppy disc for data files. They can sit at any of the

workstations and access their own files from the file server.3. A user file cannot be accessed by other people.4. A user can use any software from any station. A number of stations can access

and run the same program at the same time.5. The stations can communicate with one another- either directly or using an

electronic mail system through the file server.

Disadvantages of Local Area network1. If the file server for a network is breaks down, the user may have no data files or

software to work with.



2. A network with only a small numbers of stations is expensive. The file server has to be quite a powerful computer and cannot usually be used for anything else while the network is running.

One Network Second Network

Requirements of Network SystemHardware

1. The StationsCan be Ordinary PC’s

1. Interface to the network (Circuit Board)2. Need a cable to connect to the network3. Fewer requirements then a stand alone computer

2. A file serverA powerful computer with;

1. Large hard disk unit2. Larger main memory3. Some means of backing up the hard disk4. Possible some CD-Rom facility

3. A printer or Printersi. These need to be robust and faster than a printer for a standalone

computerii. With a computer to act as print server

4. A cabling system- securely fitted


Work S

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File ServerPrinter Printer

Work S

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File ServerPrinter Printer

Fiber Optic Cable


Software1. Network management software to:

Organize the files into user areas and maintain security; Organize backup and printing Keep data and programs going to the right places; Allow the system manager to oversee and control the network Enable users to interact with the system

2. Application softwareAll the programs being used need network or site licenses to allow a

number of users to access them at the same time.

3. People A System Manager to install software and oversee backups and changes Technicians to maintain hardware and call in engineers if necessary.

WIDE AREA NETWORKS

Diagram of a typical Wide area network

Characteristics of wide area networkComputing power for the network is usually provided by one or more ‘host’

computers. These may be remote from one another, connected by high-speed data links.The workstations are terminals or microcomputers. Often the host computers run the programs and the stations simply act as a means of communication.The network may be nationwide or even worldwideUsers usually connect to a point on the network near to them. A user connected by telephone will often be able to make a local call.PUBLIC VIEWDATA NETWORKS


Host Computer

Host Computer

Host Computer


In Britain, and in other countries, there are a number of viewdata networks available to the public. They are usually accessed using the telephone system. The user needs a terminal and a modem and has to pay a subscription.

Hardware Requirements1. This can be

A terminal this can be a visual display unit (VDU)OR

A microprocessor running a communication program, so that it behaves as a terminal.

2. A telephone line which can be used for fairly long periods.3. A modem



Software Requirements1. Users have to decide which viewdata service or services they wish to use and pay

subscription to them. For each service they will usually be given. A manual of instructions and list of services available A telephone # for the service An account Number and password (can be changed by the user later)

2. Users with microcomputers need the software to make their computers behave as terminals. This software known as communication software, will usually enable the computer to: Make the Phone call automatable Carry out most of the logging-in conversion- the user still has to type in a

password Send and receive data in the same way as an ordinary visual display

terminal Carry out the logging-out sequence and disconnect the phone

Services available on viewdata networksTele-software is software which is made available to users of a viewdata network. Programs can be received in the same way as data.A bulletin board is an area where one of a viewdata system can leave messages and information which is then available to all other users.Electronic conferencing involves a group of people having a debate or a discussion using terminals.Electronic Mail (E-mail) is a system which allows users to send messages to one another. Each user has a ‘mailbox’ – an area of the main companies store containing messages sent to them

A user can usually1. Send a message to another user2. Send a message to a group of users3. Scan the mailbox and display a list of the messages in it;4. Read any message which seems important5. Print messages out on paper;6. Send a reply to a message7. Delete or retain messages which have been dealt with.

Notes on electronic mail1. A long letter can be typed beforehand, using a word processor, and store on disc.

This is done with the terminal off-line to save a long telephone call. The user then logs on to the computer and the letter is transmitted quickly.

2. Two People using electronic mail do not have a direct conversion. One person sends a message and the other receives it latter. It is rather like sending but is faster

Gate Way to other networks



A view data network often provides its users with an option to access another network without logging out. This is called a gateway to the other networks



Access to databaseA user can search files of data for information. The files may be provided:

A group of usersOR

By professionals information providers.

Ordering Goods and serviceA user can user a viewdata service to

Book Holidays Order Airline Tickets

Examples of ViewdataCampusCampus is a British educational network used by schools and colleges. It is run by BT (British telecom) and The Times and user normal telephone lines.

The data providers are local authorities, schools them selves but also organize such as the stock exchange and the army. During the summer, the universities use Campus to publish details of places available for prospective students.Its facilities include

An electronic mail server to schools and colleges in the UK and many other countries

Database produced for and by schools Up-to-date text from British news papers Commercial database includes travel and leisure, government information and

weather data; An electronic conferencing service Information on other users and campus service A gateway to télétel, The French online service

TélételThe French on-line information service has about 7 Million users in schools, homes and business. This is partly because the terminals are provided free. However, the services have to be paid for. There are nearly twenty thousand different services available including:

Looking up telephone numbers – this was the original use of télétel; Shopping – you can order a wide variety of goods; Booking Tickets: such as from Paris to London on Euro star Electronic mail to users in France and other countries Information on shows, films and other events in Paris; Information on shows, films and other events in Paris Information about the regions of France.

InternetThe internet is a world-wide network with millions of users.It includes

An email service, which allows users to contact one another anywhere in the world. For this each user has a unique E-mail address. This is made up of strings of characters separated by full stops. The address includes information like the



user’s chosen name, the host computer their mail is stored in, their type of organization and the country they live in.

A huge network of sources of information and software known as the World Wide Web. Each individual source is called a website. Many of these sites are provided free of charge by individual any by organization such as universities.

To use the internet, as well as the usual computer, telephone and modem the user needs a subscription to an Internet access provider. This is a company which provides.

A number of exchanges so that most users can access the network with a local telephone call.

Software to interface with the network. This includes a browser- a program to search the web for information.

Advantages of viewdata1. A wide variety of interactive services2. Access to large database and other mainframe facilities

Disadvantages of viewdata1. The cost

a. Initial cost of equipmentb. Cost of telephone callsc. Charges for using some pagesd. Annual subscription for the use of the service

2. On some system response is slow and the method of searching is cumbersome.

Advantages of electronic mail over post1. Less use of paper

a. Mail can be read and replies made without printingb. A letter can be written using a word processor and transmitted direct-

again without use of paper2. Fast Delivery- Message can be received almost immediately after they are sent.3. The cost is usually the same to anywhere in the world4. Uncomplicated system. If an employee of one company sends a letter by post to

an employee of another, a chain of people is involved. Electronic mail only involves the computer system and the two people concerned.

Disadvantages of electronic mail compared with post.1. Electronic mail can only be sent to people who subscribe to the service and use

regularly2. A user dose not knows any mail has been received until he/she logs on.3. It is expensive to use a public network4. Widespread use of electronic mail might threaten the jobs of postal and office

workers.



DATA PREPARATION AND INPUTData capture means obtaining data for a computer. An input device is a peripheral which accepts data in different formats and sends it to the CPU.Data presented to the input device has to be in the right form for the device (e.g. a bar code reader will only read bar codes). The input device converts the data into a binary form which the CPU can accept.

Examples of Input Devices1. The keyboard of a microcomputer2. A light pen3. An Electronic Digital weighing interfaced to a computer4. A document reader

How data is verified

Source Data (Paper)

Typed In from KeyboardAnd stored as it is

Retyped it from source dataMatch it with previous data

Report Error if any and stored it again

Preparation and VerificationIn case of hand written forms, it has to be typed on to disk or some other input medium by a keyboard operator. Then it has to be checked to see if the typing is accurate. Then it is ready to be read by an input device.Data is originally written on a form called SOURCE DOCUMENT. The process of typing the data on to an input medium is called DATA PREPARATION. Checking the data to see that it has been typed correctly is known as VERIFICATION.

How data is verifiedTwice the data is typed by two parallel operators and cross matches it with each other. The characters are retyped correctly if necessary


Source Document

Data Typed In

Data Input Unchecked

Unverified data stored on Disc

Source Document used Again

Data Retyped making correction if necessary

Retyped Data checked against unverified data

Error Reported

Verified data stored on Disc


Note: The data could be verified by simply reading through what has been typed to see if it looks right. However, this method is not accurate enough for commercial work.



USE OF KEYBOARDWays in which keyboards are used

1. ONLINE DATA ENTRY: data is input straight to the computer which is going to process it.

2. KEY TO DISK OR KEY TO TAPE : data is prepared on tape or disc. The computer controlling the tape or disc is not one which processes the data.

3. OFF LINE PREPARATION: Data is prepared with equipment which does not use a computer.

ONLINE DATA ENTRYAdvantages

1. There is no need for special data preparation equipment.2. There is an immediate response from the computer. Data can be checked and

results obtained quickly.Disadvantages

1. Data is often not carefully prepared and verified.2. There may be an expensive use of computer time.

Uses of online data EntryResearch –Where the user wants to experiment with different inputs.Interactive use of microcomputers – in education, small businesses, etcReal time situations- booking airline ticketsUsing terminals to large computers – time sharing. Etc.

KEY TO DISK AND KEY TO TAPEKeyboard operation at key stations, the medium used may be floppy disk, magnetic tape cartridges or magnetic tape cassettes. Various systems are used, of which two are shown here.

Single station Each key station is independent of the others. There may be a facility for ‘pooling’ data from all the stations on to a magnetic tape


Data may be polled on magnetic tape before input to the computer

Magnetic Tape

Source Document

Data Typed In

Microprocessor controlled encoding and verify of data

Floppy DiskData from Other

Stations

Input to Computer


GROUP OF KEYSTATIONS CONTROLLED BY A MINICOMPUTEREach key station is in fact a terminal to a minicomputer. Usually the minicomputer can control up to 32 stations.Often preparations, verification and editing are done with the data on disc. The data is then transferred to a tape which is input to the main computer to be processed.

AdvantagesKey to disk and key to tape systems

1. The computer controlling the stations gives good facilities for checking and editing data. Time is not wasted on the main computer which will process the data.

2. Skilled operators do the work so data is accurate.

Magnetic media such as disk and tapes 1. They can be used again and again2. They can be read quickly by tape and disk units3. They store a large amount of data in a small space

Uses1. Any situation where batch processing is used2. Any situation where a large amount of data has to input to a computer system

from documents.OFFLINE DATA PREPARATION


Data Store on disc white being encoded and verified

Magnetic Tape

Source Document

Data Typed In

Microprocessor controlled encoding and verify of data

Floppy Disk

Input to Computer

Key to Tape system only. With key to Disk the disk is used as computer input

Source Document

Data Typed In


In the past most data was typed on to punched cards or paper tape using ‘punches’. These have now been largely phased out.



SECURITY AND INTEGRITY OF DATAThe security of data means the protection of data.The term refers to all methods of protecting data and software from being

1. Lost2. Destroyed3. Corrupted4. Incorrectly modified5. Disclosed to someone who should not have access to it.

Data is said to be corrupt if errors are introduced into it. Usually the errors have been introduced by faulty equipmentDanger to FILESFiles may be in danger of accidentally or intentionally being;

1. Lost e.g.a. By losing disk or tapesb. Because the file in on the system but badly named

2. Destroyed e.g.a. By fire or floodb. By deletion

3. Corrupted, e.g.a. By scratches on a disc or faulty disc drives.b. By interference during a communication

4. Modified, e.g.a. By being unintentionally written over;b. For malicious reasons such as fraud;c. By being updated with incorrect data

5. Accessed by unauthorized people

HackingHacking means obtaining access to a computer system without authorityNotes: Many examples of hacking for fraud are by programmers within the company concerned.Hacker: A person, more commonly considered a cracker, who uses computer expertise for illicit ends, such as by gaining access to computer systems without permission and tampering with programs and data. Hackers from outside often use a modem from their own home computer to connect to the computer being hacked

Examples of hacking incidentsA hacker caused a cancer Research center’s computer to close down for a day by overloading it. He caused it to run programs which made thousands of telephone calls and cost a lot of moneyOther hackers have gained access to the electronic mail boxes of famous people

Protection Again HackingThere are various ways to make hacking less likely;



1. By the use of passwords for users and for individual files. Great care should be taken in choosing and in securing passwords

2. by encrypting files3. By arranging for a network system to be unfriendly to strangers for

example to disconnect a user after 3 unsuccessful attempts to key a password.

Hacking is defiantly a criminal offence- with very swear penalties. The computer Misuse Act of 1990 creates three main type of offence:

operating a computer to gain unauthorized access to programs or data; Impairing the operation of computer by altering programs or data; gaining access to a computer in order to commit a crime such as fraud;

VirusA computer virus is a program which copies it self without the user indenting to it.

Notes: i. Often a virus attaches itself to other programs which are then saved with the

virus adding to them. Most viruses do not affect data files.ii. The virus usually dose more then just copy it self. It may erase files or

corrupt the data on the screen.Examples;

1. the Michelangelo virus This infects files. Until 6th march, which was Michelangelo’s birthday? On

that day, if not stopped, it deletes the files on the hard disk of any infected computer.

2. the cascade virus This also have particular dates when it becomes active, casing all

characters on the screen to fall in a jumbled mass to the bottom of the screen.

Protection against VirusesViruses cost commercial firms a great deal of money. Even if their computers are not infected, they have to spend money making sure viruses are not introduced. Steps they can take are:

1. Make sure every one in the organization knows of the danger.2. Use a commercial program which deducts any viruses. Manu of these can say

which viruses are present and get rid of them.3. Avoid the use of any programs of doubtful origin, such as “Free” software4. Backup files on a regular base. This may not get rid of the virus, but if it deletes

files, at least they can be recovered. 5. Make standards software right protected, so that a virus cannot change it.

Note: a virus program which doses nothing dangerous is more likely to spread because people do not notice it.

Making Copies of file is a copy of files.A backup file is a copy of a file which is kept in care anything happens to the original file.



Example of backfiles files1. Backup on saving

In word processor the old file is given a name ending in BAK so that user can easily recognize. i.e. Letter.bak is the old version of Letter.doc

2. Timed backupThis option is useful if there is a power failure. The word processor automatically

saves the document in every 15 minutes.3. Making a duplicate file always when you save a file

Note: backup files and archives use a large amount of storage. Methods are devised of storing the data in a smaller space.

Other ways of looking after dataPhysical safeguards

1. Locking files away: Important data stored on floppy sick should kept in safe place2. Protecting files against being over written: Make files read only.3. Keeping people out: Only authorized personal are allowed

Software SafeguardsA user identity is a name or number by which the system knows that user. Each user identity given an area of backing store in which files, often the user can decide which Other user can access these files.A password is a set of characters which a computer associates with a particular user identity. A password is usually kept secret and the computer dose not display it on the screen as it is typed in.To log in means to gain access to a system by giving the correct instructions and responses.To logout means to exit from a system by giving the correct instructions

Advice About passwords1. Choose a sequence containing no fewer than six characters2. Pick something you can remember but no one else would think of, even if they

know you3. Never tell anyone what it is4. Never write it down5. Be careful who is looking over your shoulders.6. Change it every week or so

Note: When a password or PIN is changed the system usually asks the user to key the new password twice to ensure that it has been keyed correctly.

Other Software Safeguard1. Some files may only be accessible to certain passwords.2. On some systems users may be able to give files an access code. i.e. a file may be

made ‘read only’3. Individual files may be given passwords4. Data encryptions



To ENCRYPT DATA is to encode it in such a way that it is unreadable to anyone who dose not knows how to decode it.

METHODS OF DETECTING INPUT ERRORSVerification of Data:Verification is the checking of data which has been copied from one place to another to see that it still represents are original data.Example of verification of data: Key to disc encoding- double entry.In a computer bureau, data is being encoded on to disc by first user. The data is verified by second user who rekeys it all. The computer controlling the key station checks the data stored the data now being typed and reports differences, so that any errors can be corrected.

Validation of dataValidation is the checking of data before Data validation, the process of testing the accuracy of data before processing to see that it is acceptable for the process.

Note: validation may be carried out by the program which is to process the data or by a separate program.A check to see it is in the right format;A type check- that it is of the right type e.g. a numberA length check- that it has the right number of characters;A range Check – that it is within the range of possible values;A presence check – that some data has in fact been keyed;A table look-up – checking through a set of possible values to see if the data is one of them Examples of validation ChecksA type check

Like age is not a fractional part it must be a whole #A range Check

The day us between 1 and 31 inclusive; The month is between 1 and 12 inclusive

Note: 1. all parts of the date are numbers (a type check)2. February has 29 days in a leap year and only 28 days in other years.



Document ReaderA document reader is a device which can read data straight from forms.

Examples of documents read by document readersA card on which pencil marks are made by handA multiple choice question paper with pencil marks to shows the candidate’s choices.A bank cheque with number along the bottom in magnetic inkA slip filled in by a gas board meter reader. The custom’s address and account number are printed by a line printer. The meter reading has been filled in a pencil.

Types of data read by documents readers.1. Marks

Short lines made by hand- they are usually in pencil on cards or documents.2. Handwritten characters

When documents are to be filled in by hand they are preprinted with spaces provided. The characters have to be written carefully in the right places

3. Printed LinesThe most common of these is the bar code

4. Printed charactersa. Numbers which have been output on to documents by a line printer.b. Magnetic ink characters on bank cheques

Methods of reading marksMark sensing Small electrical ‘brushes’ touch the surface of the document or card. When they contact a pencil mark a circuit is completed. The marks must be in a soft pencil as this contains graphics, which conducts electricity.Optical mark reading (OMR)A beam of light is directly on to the surface of the card or document. The beam is reflected from the surface to a light sensor. When a mark passes under the beam less light is reflected back and the presence of the mark is registered.

AdvantagesOf OMR compared with mark sensing

The sensitivity of optical readers can be altered to allow for different surfaces and different pencils or inks.

Of Mark compared with handwriting charactersThere are fewer recognition failures.

Of marks and characters compared with keyboard preparation 1. data can be prepared at the place where it originates2. No machines are required for the preparation.

DisadvantagesOf marks compared with characters

Documents for mark readers are more complicated. If an item has several values then a mark space has to be allocated for each value.



Of marks compared with data prepared using a keyboard.1. Input of data to the computer is a slow. For example a marked card reader is far

slower than a disk unit.2. It is difficult to verify marked data.3. Document for a mark reader are difficult to understand and to fill in.4. A document reader has to be reprogrammed for each new design of document.

Using the mark ReadingIn situation where.

1. The data to be input is simple2. The volume of data is large enough to justify designing special documents for it.

Examples of uses1. For multiple choice examination paper2. For data collection in the field by research workers3. For market research questionnaires4. In supermarkets for recording stock

CHARACTER RECOGNITIONDescriptionThe document reader recognizes character which have been printed by machine or by hand the shape of each character is analyzed by the document reader and compared with a set of known shapes, and either the character is recognized or the document is rejected to be dealt with in another way.

Methods of inputting charactersOptical character shapes are recognition (OCR)

The character shapes are recognized by sensing light reflected from the paper and from the ink (As with OMR) but the reader has to have a memory and a processing capability in order to work out the character.A device that reads text from printed paper by detecting the pattern of light and dark on a page and then applying optical character recognition methods to identify the charactersThe process in which an electronic device examines printed characters on paper and determines their shapes by detecting patterns of dark and light. Once the scanner or reader has determined the shapes, character recognition methods—pattern matching with stored sets of characters—are used to translate the shapes into computer text. Acronym: OCR.

FONT. A set of characters of the same typeface (such as Garamond), style (such as italic), and weight (such as bold). A font consists of all the characters available in a particular style and weight for a particular design; a typeface consists of the design itself. Fonts are used by computers for on-screen displays and by printers for hard-copy output. In both cases, the fonts are stored either as bit maps (patterns of dots) or as outlines (defined by a set of mathematical formulas). Even if the system cannot simulate different typefaces on the screen, application



programs may be able to send information about typeface and style to a printer, which can then reproduce the font if a font description is available. See also bit map, font generator.

Magnetic-ink character recognition A form of character recognition that reads text printed with magnetically charged ink (Iron Oxide), determining the shapes of characters by sensing the magnetic charge in the ink. Once the shapes have been determined, character recognition methods are used to translate the shapes into computer text. A familiar use of this form of character recognition is to identify bank checks. Acronym: MICRReaders usually read a font known as font E13B (at least in this country) this contains only 14 characters- the digits 0-9 and four special symbols.

Advantages Of MICR over OCR

It is difficult to forge (create a fake copy)Documents can still be read when folded, written on, etc.

Of OCR over MICRMore difficult fonts can be used, including sometimes hand printing and normal type.

Of characters compared with marksDesign of forms is less complicated.

Of characters over other mediaData can be read by other people

DisadvantagesOf MICR compared with other media.

Readers are very expensiveOnly certain fonts are acceptable

Of hand-printed charactersThere is high rejection rate

Of printer charactersA high standard of printing is required.

Uses Of MIRCWhere printed Numbers is a standard format are to be read in large volume i.e. the major British banks all use MICR to encode along the bottom of cheques the following information:

a) Cheque Numberb) Branch Number of the bankc) The customer’s account Numberd) (After the cheque has been banked) the amount of money

OF OCRSituations where data has been typed or printed for people to read, If OCR is used the data dose not need to be retyped for entry to our computer. It is particularly useful for



turn around documents, where some characters are printed by our computer printer and other are added later by hand.I.e. in the case of our charity fund, where names and address of prospective donors are preprinted on donation forms, each donor send back a form with some money. The date and amount given our carefully hand printed on the form by an operator.

BARCODES, TAGS AND MAGNETIC STRIPSMany of the places we visit as customers our becoming progressively more automotive. This includes shops, banks and libraries. Computer input media are being used which allow assistance to serve us quickly without having to write things down. Food containers and library book have barcodes on them; cloths and shoes have card board tags; we can take money form a bank using a plastic card. With our going in side the bank.The secret of all these input media is that the data has been put on them. Long before the transaction take place. I.e. barcodes are printed on food labels before they are packed. To record the sale of the food no one has to write or type anything. All that is needed is a bar code reader.Bar codes DescriptionBar Code The special identification code printed as a set of vertical bars of differing widths on books, grocery products, and other merchandise. Used for rapid, error-free input in such facilities as libraries, hospitals, and grocery stores, bar codes represent binary information that can be read by an optical scanner. The coding can include numbers, letters, or a combination of the two; some codes include built-in error checking and can be read in either direction.

A bar code is a set of parallel printed lines of differing thicknesses (usually alternately black & white), which represent a number. Often a number represented by the bars is also printed above or below the barcode. When barcodes are used on shop goods, the number coded identifies the product, giving usually a number code for;

1. country of origin2. manufacturer3. An item Number for the product.

Note: because prices change so much they are not recorded on barcodes. The prices have to be stored in a computer, which is used when a price is needed.

Bar Code Scanner An optical device that uses a laser beam to read and interpret bar codes, such as the Universal Product Codes found on grocery products and other retail items. See also bar code, Universal Product Code

AdvantagesBar code can be printed by normal printing Methods.The type of item or its price dose not have to be repeatedly written down or types.

DisadvantagesBarcodes cannot be changed, and thus are unsuitable for recording pricing, Customers still have to be informed of prices (e.g. by labels or catalogs).



Barcode can only be read by machine.Only numbers can be coded in this way.

Magnetic StripsA magnetic Strip is a short length of magnetic tape stuck on to the surface of tag, card, document. On plastic tags or cards the strip is sealed in. Tags with strips identify the item they are attached to.Cards often only store enough data to enable a computer to identify the owner (e.g. bank cards).

Examples of the use of Magnetic Strips1. On cards called visual record cards. A special encoder is used. A keyboard

operator types data which is printed on the front of the card. At the same time it is encoded on the magnetic strips on the back of the card. People can read the printed information and a computer can read the magnetic strip

2. On credit cards.A shop or business with a terminal can have the card checked to see that the owner is credit worthy.

3. On bank Cards: Bank issue plastic cards with a magnetic strip for various purposes Examples are;

a. For a customer to present when writing a cheque. The banks will then guarantee to accept cheques up to a certain limit.

b. to use in a cash issuing terminal 4. As tags on cloths5. As a phone card, some telephones do not accept coins. Instead a card is used

which has been bough previously at a post office. The vale of the card is recorded on a magnetic strip. As a user makes a call the number of units stored on the card is reduced.

Advantages of the magnetic Strip1. It is simple to produce.2. it is not easily damaged (accept by magnetic fields)3. its stores a fairly large number of characters

Disadvantages of the magnetic StripThe data can be changed or erased by magnetic fields

NEW DEVELOPMENTSNew methods of storing data on cards have become available they include;

1. laser cardsData stored on these as small holes in a polished surface. The cards are read using reflected light. Some readers contain a laser but cheaper versions do not.One card can store over 2 million characters

2. Smart CardsThese have a very thin ROM chip sealed into them



One card can store about 8 thousand characters.

INPUT AT TERMINALS AND MICROCOMPUTERSKeyboardsUsually a VDU or a microcomputer is provided with a keyboard for input this usually has on it keys with:

1. The alphabet2. The Numbers

Often Numbers appear twice – once a long the top as they would on a type writer and again in a key pad at the write. The separate keypad can be used when all the data is numerical. The other row can be used

3. Characters for punctuations ( . , : ; etc.).4. Other text characters (Mathematical Symbols % & # etc)5. Cursor movement , Editing functions (DELETE , COPY, etc.), control characters

(ENTER or RETURN, EXCAPE)The keyboard also has keys which change the function of other keys SHIFT, CAPS—for capital letters, CTRL for control functions, etc.).



Light Pen. An input device consisting of a stylus that is connected to a computer’s monitor. The user points at the screen with the stylus and selects items or chooses commands either by pressing a clip on the side of the light pen or by pressing the light pen against the surface of the screen. It deducts the presence or absence of light. Electrical signals are sent along the cable indicating whether or not light of sufficient intensity is being sensed.

Types of use1. To detect bar codes.2. To indicate a point on a screen. The pen is pointed at the appropriate place

Examples 1. The pen is used to choose one of the selection of options printed i=on the screen,

by pointing it at the option required.2. Drawing are produced on the screen by using a special function pad and a key

board to indicate what the computer should draw and the pen to point out where it should draw it.

Advantages1. It removes the need to type or write2. It is faster then typing

Disadvantages1. It can record only the presence or absence of light.2. It only works with software written for it.

Note: for screen work, light pens may eventually be replaced by touch sensitive screens, which enables a finger placed on the screen to indicate a position.

Mouse: Mouse a common pointing device. The basic features of a mouse are a flat-bottomed casing designed to be gripped by one hand, one or more buttons on the top, a multidirectional detection device (usually a ball) on the bottom, and a cable connecting the mouse to the computer. By moving the mouse on a surface (such as a desk top), the user typically controls an on-screen cursor. A mouse is a relative pointing device because there are no defined limits to the mouse’s movement and because its placement on a surface does not map directly to a specific screen location. To select items or choose commands on the screen, the user presses one of the mouse’s buttons, producing a “mouse click.”



Mouse. Two types of mouse: for the Macintosh (left) and for the PC (right).

Opt mechanical mouse a type of mouse in which motion is translated into directional signals through a combination of optical and mechanical means. The optical portion includes pairs of light-emitting diodes (LEDs) and matching sensors; the mechanical portion consists of rotating wheels with cutout slits. When the mouse is moved, the wheels turn and the light from the LEDs either passes through the slits and strikes a light sensor or is blocked by the solid portions of the wheels. These changes in light contact are detected by the pairs of sensors and interpreted as indications of movement. Because the sensors are slightly out of phase with one another, the direction of movement is determined based on which sensor is the first to regain light contact. Because it uses optical equipment instead of mechanical parts, an opt mechanical mouse eliminates the need for many of the wear-related repairs and maintenance necessary with purely mechanical mice, but it does not require the special operating surfaces associated with optical mice. Optomechanical mouse.

Optical mouse. Small lights under the mouse are reflected in to photoelectric cells. These detect when a line is crossed. This type of mouse only works on a grid of lines. A type of mouse that uses a CMOS digital camera and a digital signal processor to detect motion. The camera photographs the surface over which the mouse moves 1500 times per second,

and the digital signal processor uses the photographs to convert the mouse movement into onscreen movements of the cursor. IntelliMouse Explorer and IntelliMouse with IntelliEye, two optical mouse models with no moving parts and requiring no special mouse pad, were introduced by Microsoft in 1999. See also mouse. 2. A type of mouse that uses a pair of light-emitting diodes (LEDs) and a special reflective grid pad to detect motion. The two lights are of different colors, and the special mouse pad has a

grid of lines in the same colors, one color for vertical lines and another for horizontal lines. Light detectors paired with the LEDs sense when a colored light passes over a line of the same color, indicating the direction of movement.



UsesTo select options form a menu or form a set of icons.To position the cursor when editing text or using a design package.To draw shapes.



Advantages of using a mouse 1. It is easy and convenient to use2. It selects a position on the screen more quickly then is possible with a keyboard.

Disadvantages1. Its only works with software written on it2. It cannot be used to input-it has to used with keyboard.3. It is not very accurate for drawing purposes.

JOYSTICKJoystick. A pointing device used mainly but not exclusively for computer games. A joystick has a base, on which control buttons can be mounted, and a vertical stem, which the user can move in any direction to control the movement of an object on the screen; the stem may also have control buttons. The buttons activate various software features, generally producing on-screen events. A joystick is usually used as a relative pointing device, moving an object on the screen when the stem is moved and stopping the movement when the stem is released. In industrial control applications, the joystick can also be used as an absolute pointing device, with each position of the stem mapped to a specific location on the screen.

Uses1. Controlling objects in computer games2. Producing graphics

Comprising between a mouse and a joy stick The function of a mouse and a joy stick are similar. The joystick allows the faster interaction need in games. The mouse is suitable for office use. In particular, the mouse is often used with windows and icons. Program using windows, icons and a mouse to move a pointer are often called WIMP packages. (The P can also stand for pull-down menu that is a menu which appears when you click a mouse button.

GRAPHIC TABLETA device used to input graphics position information in engineering, design, and illustration applications. A flat rectangular plastic board is equipped with a puck or a pen



(also called a stylus) and sensing electronics that report the position of the puck or stylus to the computer, which translates that data into a cursor position on the screen.

STYLUS A pointing device, similar to a pen, used to make selections, usually by tapping, and to enter information on the touch-sensitive surface.PUCK A pointing device used with a graphics tablet. A puck, which is often used in engineering applications, is a mouse like device with buttons for selecting items or choosing commands and a clear plastic section extending from one end with cross hairs printed on it. The intersection of the cross hairs on the puck points to a location on the graphics tablet, which in turn is mapped to a specific location on the screen. Because the puck’s cross hairs are on a transparent surface, a user can easily trace a drawing by placing it between the graphics tablet and the puck and moving the cross hairs over the lines of the drawing.

Puck.

AdvantagesIt can be used to digitize drawings with great accuracy

UsesDigitizing maps- e.g. the Ordnance Survey is storing many of its maps on magnetic tape.Reproducing drawings and designsProducing layouts for the printed circuit boards used in the circuitry of computers and other devices

Note: Some types of graphics tablet will accept hand-written numbers and letters. This type is sometime known as a DATA PAD. It is not suitable for inputting a large amount of data. Data input in this way has to be checked on a screen as it is written to see that it has been recognized correctly.

OTHER INPUT DEVICESVoice Recognition MethodThe capability of a computer to understand the spoken word for the purpose of receiving commands and data input from the Microphone. Systems that can recognize limited vocabularies as spoken by specific individuals have been developed, but developing a system that deals with a variety of speech patterns and accents, as well as with the



various ways in which a request or a statement can be made, is more difficult, although advances are being made in this area.

AdvantagesNo typing or data preparation is necessaryIt can be use remotely by telephone, or by those who are handicapped or who have their hands occupied



DisadvantagesAt present the method does not give good results. Relatively few words can be recognized and the error rate is highRecognition is slowIt is not suitable in noisy places without a shielded mouthpiece

Uses1. Where only a few different commands are to be given and the hands cannot be used,

for example by a helicopter pilot to produce a display of a appropriate instructions on the screen, using presto red voice commands.

2. Over the telephone, for example by a bank. The computer can recognize a caller from a spoken code, tell him/her the state of a requested account and accept simple commands such as ‘repeat’

3. By handicapped people to control equipment.

Direct Input from instrumentsMany measuring devices are now digital and electronic and can be linked to a computer. This requires special software to make use of the data coming in and, usually, a special interface between the device and the computer.

Examples of direct input1. Thermostats or thermometers connected to a computer controlling a heating system2. A pressure pad on a road connected to a computer controlling traffic lights.3. The instruments in a space vehicle interfaced with a computer which calculates the

flight path and control the rockets.

SCANNERFlatbed scanner a scanner with a flat, transparent surface that holds the image to be scanned, generally a book or other paper document. A scan head below the surface moves across the image. Some flatbed scanners can also reproduce transparent media, such as slides. See the illustration. Compare drum scanner, handheld scanner, sheet-fed scanner.



OUTPUT DEVICESOutput device is a peripheral which receives data in the form of electrical pulses from the central processing unit. It then converts this data into information or into further data.Often the information output is in a form that people can read. ExamplesPay slips produced on a line printerProgram listings produced on a screen

Sometime the information is not the form of words or numbers, ExamplesMaps or design on screen or on a plotterSounds simulating a musical instrumentalA synthesized human voice

Sometime data is output which is to be read by machines. This may be used as input for computers or other equipment. ExamplesInstruction to control a programmable lathe, These can be output on to a magnetic tape by a computer; The tape can be then be input to the lathe. Which has its own tape unit?Data is stored on a floppy disc by one computer to be input to another. An Example of this is an insurance company where a disk of customer information is produced on a microcomputer at a branch office. This is then sent on to the company’s head office to be used on their main computer.



Preprinted StationaryConsist of sets of identical forms or documents. These are fed into a computer printer instead of plain paper. Data is then printed on them in appropriate placesThe method is only suitable For computers applications which involves a large amount of similar outputWith a printer which can be fed different types of stationary

ExamplesBills for public services such as rates, gas, electricity, etc.Pay slipsMost of the meter reading forms is preprinted

OUTPUT ON SCREENIn recent years we have seen:Better communicationFaster CommunicationsVastly increased storageWidespread use of microcomputers

There has been a dramatic increase in:The amount of data being looked atThe interactive use of computersThe use of graphics and animationsDefinition

The resolution of the screen is a measure of how accurately data can be represented on it. Screens are usually classed as low resolution, Medium resolution or high resolution.For example, a low-resolution screen would be suitable for viewdata or teletext. It world be not suitable for CAD

PIXEL, Short for picture (pix) element. One spot in a rectilinear grid of thousands of such spots that are individually “painted” to form an image produced on the screen by a computer or on paper by a printer. A pixel is the smallest element that display or print hardware and software can manipulate in creating letters, numbers, or graphics.

Pixel. The letter A is actually made up of a pattern of pixels in a grid, as is the cat’s eye.



Monochrome Display1. A video display capable of rendering only one color. The color displayed depends on the phosphor of the display (often green or amber). 2. A display capable of rendering a range of intensities in only one color, as in a gray-scale monitor. Displays images in only one color—black on white (as on early monochrome Macintosh screens) or amber or green on black3. The term is also applied to a monitor that displays only variable levels of a single color, such as a gray-scale monitor.

Cursor 1. A special on-screen indicator, such as a blinking underline or rectangle that marks the place at which a keystroke will appear when typed. 2. In reference to digitizing tablets, the stylus (pointer or “pen”). 3. in applications and operating systems that use a mouse, the arrow or other on-screen icon that moves with movements of the mouse.

STORAGE OF THE CONTENTS OF A SCREENA screen dump is a transfer of every thing on a screen to some other medium. This is usually a printer or a plotter, but could be a disc or a magnetic tape. The dump is carried out using a special program for the purpose.Screen dump, a duplicate of a screen image; essentially, a snapshot of the screen that is either sent to a printer or saved as a file. TThe data displayed on a screen has to be represented as binary codes because

1. It is stored in RAM while it is being displayed2. That it can be transmitted e.g. teletext, view data etc.3. That it can be saved by dumping it on to backing store or on to a printer.

Each pixel needs one bit of storage on a monochrome screen. Color screen pixel needs 2 bits for 4 color and 4 bits for 16 colors. Thus large amount of storage is required to store the contents of the screen because.

1. The screen has a high resolution.2. Each pixel can have a lot of different color.

Screen ModesA screen mode is a way a computer uses the screen for graphics and text

Resolution, 1. The fineness of detail attained by a printer or a monitor in producing an image. For printers that form characters from small, closely spaced dots, resolution is measured in dots per inch, or dpi, and ranges from about 125 dpi for low-quality dot-matrix printers to about 600 dpi for some laser and ink-jet printers (typesetting equipment can print at resolutions of over 1000 dpi). For a video display, the number of pixels is determined by the graphics mode and video adapter, but the size of the display depends on the size and



adjustment of the monitor; hence the resolution of a video display is taken as the total number of pixels displayed horizontally and vertically.

High Resolution. The capability for reproducing text and graphics with relative clarity and fineness of detail. High resolution is achieved by using a large number of pixels (dots) to create an image in a given area. For screen displays, the resolution is stated in terms of the total number of pixels in the horizontal and vertical dimensions. For example, the VGA video adapter has a resolution of 640 by 480 pixels. In printing, resolution refers to the number of dots per inch (dpi) produced by the printer, such as 300 to 600 dpi for a desktop laser or ink-jet printer or 1000 to 2000 dpi for a production-quality image setter

Low resolution. Abbreviated lo-res. Appearing in relatively coarse detail, used in reference to text and graphics in raster-oriented computer displays and printing. Low-resolution printing is comparable to draft-quality dot-matrix output printed at 125 dots per inch or less.

Examples of screen modes1. In 25 lines of text with 40 characters each; graphics are produced using 320 pixels

across and 256 pixels down; 4 colors are available2. In 25 lines of text with 80 characters each; graphics are produced using 640 pixels

across and 256 pixels down; 16 colors are available

Worked QuestionsA particular high-resolutions screen has 640 pixels across it and 512 pixels down. Each pixel can display any of 16 different colors

Question: How much K (Kilo Bytes) needed to store the screen?Answer: Each pixel can have 16 color

Thus it needs 4 bits to storeOne byte contains 8 Bits2 pixel can be store in each byte1 kilo byte = 1024 Bytes

Number of K = ½ * (640*512)/1024

TYPES OF SCREENSStandard television setsAn ordinary home television can be used as a computer output. However, these sets are only designed to receive broadcast television. The picture are not steady and have low resolutions

USE1. As a cheap display device for home computers



2. For teletextMONITORSA monitor is a high resolution viewing unit. It looks like a television set but it accepts different type of input signals. It has a far steadier, more clearly defined picture.

UseAlmost all display screens in business and professional use are monitors



CRT . Acronym for cathode-ray tube. The basis of the television screen and the standard microcomputer display screen. A CRT display is built around a vacuum tube containing one or more electron guns whose electron beams rapidly sweep horizontally across the inside of the front surface of the tube, which is coated with a material that glows when irradiated. Each electron beam moves from left to right, top to bottom, one horizontal scan line at a time. To keep the screen image from flickering, the electron beam refreshes the screen 30 times or more per second. The clarity of the image is determined by the number of pixels on the screen.

LCD Liquid Crystal Display consists of two thin sheets of glass with liquid crystals between them. Characters are etched on the inner sheet but cannot be seen them on the outer sheet only when a current is passed through them. Only a limited number of characters can be shownA type of display that uses a liquid compound having a polar molecular structure, sandwiched between two transparent electrodes. When an electric field is applied, the molecules align with the field, forming a crystalline arrangement that polarizes the light passing through it. A polarized filter laminated over the electrodes blocks polarized light. In this way, a grid of electrodes can selectively “turn on” a cell, or a pixel, containing the liquid crystal material, turning it dark. In some types of liquid crystal displays, an electroluminescent panel is placed behind the screen to illuminate it. Other types of liquid crystal displays are capable of reproducing color.

USE1. As screens for small portable microcomputers2. As display for Electronic Calculators and watches

Other Types of Screen1. Display consist of light-emitting diodes (LED’s), These use more power then LCD

display but are brighter2. Plasma Display Panels; These use gas between gas plates instead of liquid and may

make possible flat screen for monitors.



PRINTERS

A computer peripheral that puts text or a computer-generated image on paper or on another medium, such as a transparency film. Printers can be categorized in any of several ways: impact versus non-impact; print technology; character formation; method of transmission; method of printing; print capability; and print quality.

Character PrintersCharacters are printed one by moving across and down the page

Line Printer, Any printer that prints one line at a time as opposed to one character at a time (as with many dot-matrix printers) or one page at a time (as with some dot-matrix and most laser printers). Line printers typically produce the familiar 11-by-17-inch fanfold “computer” printouts. They are high-speed devices and are often used with mainframes, minicomputers, or networked machines rather than with single-user systems

Page Printer, Any printer, such as a laser printer, that prints an entire page at once. Because page printers must store the entire page in memory before printing, they require relatively large amounts of memory.

IMPACT VERSUS NONIMPACT PRINTER The most common distinction is impact versus no impact1. Impact printers physically strike the paper and are exemplified by pin dot-matrix

printers and daisy-wheel printers; non-impact printers, dot-matrix printers can be further classified by the number of pins in the print head: 9, 18, 24, and so on.

2. Every other type of print mechanism is known as non-impact printers, including laser, ink-jet, and thermal printers.

HOW CHARACTERS ARE FORMED- THE FONTThe most common types are1. Matrix font- each character is made up of dots selected from a rectangular matrix.2. Solid fonts- the characters are produced using pieces of shaped metal as on an

ordinary mechanical typewriter



MAIN TYPES OF PRINTERSPage PrinterThe most common of these is the laser printer:Laser printer an electrophotographic printer that is based on the technology used by photocopiers. A focused laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum. This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper. Finally, the electrical charge is removed from the drum, and the excess toner is collected. By omitting the final step and repeating only the toner-application and paper-handling steps, the printer can make multiple copies. The only serious drawback of a laser printer is that it offers less paper-handling flexibility than do dot-matrix printers. Both multipart forms and wide-carriage printing, for example, are better handled by line printers or dot-matrix printers.Larger laser printers are powerful and can print up to 150 pages a min. this type are useful will mainframes printers. Recently smaller laser printer have been introduced for use in small installations and in office. These produce up to 20 pages a minute.

Advantages1. They are very fast2. They give very high quality printing3. They are quiet, because they are non-impact

Disadvantages1. Expensive to buy2. Expensive to run

LINE PrintersInk-jet printer or inkjet printer n. A non-impact printer in which liquid ink is vibrated or heated into a mist and sprayed through tiny holes in the print head to form characters or graphics on the paper. Ink-jet printers are competitive with some laser printers in price and print quality if not in speed. However, the ink, which must be highly soluble to avoid clogging the nozzles in the print head, produces fuzzy-looking output on some papers and smears if touched or dampened shortly after printing.BAND or Train PrintersThe characters set is in a continuous loop of characters. Usually the complete character set is repeated several times round the loop.The loop rotates in a horizontal line. There is a set of hammers across the paper. The hammer for each character positions hits the paper and a carbon on the right character as it goes past.

AdvantagesOf ink jet over band

1. They are faster2. They are quiet



3. They give far better quality printingOf band over ink jet

1. They are more reliable2. They are less expensive to buy3. They can print several copies using carbon paper between the copies

Of line printers over character Printers1. They are faster

Character PrintersDot Matrix PrintersAny printer that produces characters made up of dots using a wire-pin print head. The quality of output from a dot-matrix printer depends largely on the number of dots in the matrix, which might be low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot-matrix printers are often categorized by the number of pins in the print head—typically 9, 18, or 24

Solid FontThe character set is a set of shaped characters actually on the printing head. Like solid font printing heads are Golfball. Where the printing head is spherical, and daisy wheel, where the printing head is a spooked wheel, made of metal or plastic and about 80 min in diameters, with character at the ends of the spokes

Type Ball A small ball mounted on the print head of a printer or a typewriter that bears all the characters in the character set on its surface. The ball rotates to align the correct character with the paper and with an inked or carbon ribbon before striking against the paper

Daisy-Wheel Printer A printer that uses a daisy-wheel type element. Daisy-wheel output is crisp and slightly imprinted, with fully formed characters resembling typewriter quality. Daisy-wheel printers were standard for high-quality printing until being superseded by laser printers.

Non-impactPrinters which rely on the paper and the print head hitting each other are noise. Various methods have been developed of avoiding this, although at present they are not popular as impact printers.

AdvantagesOf non-impact over impact

They are very quiet



Of impact over non-impactThey can produce multiple copies using carbon paper

Of daisy wheel over dot matrixThe characters are better formedThey are quitter

Of dot matrix over solid fontThey are less expensive for a given speed

Of character printers generallyThey are cheap and reliable

DisadvantagesOf Daisy wheel printers

The daisy wheels wear quicklyOf character printers generally

They are far slower than page or line printers



PlottersPlotter. Any device used to draw charts, diagrams, and other line-based graphics. Plotters use either pens or electrostatic charges and toner. Pen plotters draw on paper or transparencies with one or more colored pens. Electrostatic plotters “draw” a pattern of electrostatically charged dots on the paper and then apply toner and fuse it in place. Plotters use three basic types of paper handling: flatbed, drum, and pinch roller. Flatbed plotters hold the paper still and move the pen along both x and y axes. Drum plotters roll the paper over a cylinder. The pen moves along one axis while the drum, with the paper attached, moves along the other. Pinch-roller plotters are a hybrid of the two, in which the pen moves only along one axis while the paper is moved back and forth by small rollers.

Plotters can be used on-line or off-lineOnlineA plotting program running in a computer produce binary data which is sent directly to the plotter to control its movement.

Offline The plotting program produces the same data as before but the data is usually stored on magnetic tape. This tape can be used to produce a plot later. Without the computer being involved, by using a reader attached to the plotter

Advantage of line use of plotterBecause of the slow movement of the pen, plotters produce output fairly slowly in comparison with other output devices. The offline method allows plot data to be output to a high speed medium, thus saving computer time.

Types of Digital Pen Plotters Flatbed Plotter A plotter in which paper is held on a flat platform and a pen moves along both axes, traveling across the paper to draw an image. This method is slightly more accurate than that used by drum plotters, which move the paper under the pen, but requires more space. Flatbed plotters can also accept a wider variety of media, such as vellum and acetate, because the material does not need to be flexible. See also plotter. Compare drum plotter, pinch-roller plotter.

Drum Plotter A plotter in which paper is wrapped around a large revolving drum, with a pen that moves back and forth at the uppermost point on the drum. The paper is rolled with the drum to align the correct point on the paper with the pen. Drums take up a fraction of the space required by flatbed plotters that can handle the same paper size. They also effectively have no limit on the length of the paper they can handle, which can be an advantage in some applications. See also plotter. Compare flatbed plotter, pinch-roller plotter.

UseIn any situation where hard copy of graphical output is required, for example to output design which have been developed using a graphical display unit, or to produce maps.



OTHER OUTPUT METHODSCOMPUTER OUTPUT ON MICROFICHE OR MICROFILM A miniature display screen or a laser is used to produce output, much reduced, on high-quality film. Microfiche is a rectangular sheet of microfilm large enough to contain a number of pages of data- typically 30 to 300.Because of the reduction in size microfilm or microfiche cannot be read without a special reader to project the image on to a screen. With microfiche the material has to be moved into the correct position as only a small part of it is displayed on the screen. The microfiche reader is often fitted with fine adjustments to enable this to be done accurately.

AdvantagesOver output on to paper

2. Graphics and/or text can be produced at very high speed3. A large amount of data can be stored in a very small space.

DisadvantagesCannot be read without special equipmentCannot be written on by hand

USESto produce large quantities of output for store in a small spaceTo make data easy to carry around or send by post.

VOICE OUTPUTSpeech synthesis. The ability of a computer to produce “spoken” words. Speech synthesis is produced either by splicing together prerecorded words or by programming the computer to produce the sounds that make up spoken words

AdvantagesCan be accessed by telephoneNo reading ability is required by the user

DisadvantagesIt is not suitable for noisy environmentThere is no permanence- Words not understood have to be repeated by the computer

USETo produce a response from a computer by telephone without the need for a modem or terminal equipment at the user’s end of the line. If a push-button telephone is used, coded messages can be sent by presenting combination s of the button and the computer replies with synthesized speech.Small hand held devices are available which produce synthesized speech and which canMake learning more interestingHelp with the translation of foreign language.

DIRECT OUTPUT TO OTHER DEVICES



1. Digital to analog converters. This is because computers output digital signals. The device that computers control are often analog

2. Actuators- an actuators is a device which can produce a movement when given an electrical signal.

3. Devices to switch large currents on and off. A computer only produces very low-power electrical signals. These cannot drive electrical equipment. To get a computer to do this the signal from a computer has to switch another device on and off. Devices are

a. Transistors- a transistor can be used to switch on and off without any mechanical movement

b. Relays – a relay is a switch which can be switched on and doff by a small current. It does involve a mechanical movement, but it can be used to switch more powerful equipment than can a transistor. In particular a relay can be used to switch on and off machines which work on main electricity

4. Motors- Two types of motor might be used in a computer-controlled systema. A continuous Motor This runs continuously and evenly when it is

switched on. This type of motor has the advantage that it can run at high speeds.

b. A stepper motor- When a signal is sent to repeated signals. A stepper motor has the advantage that it can be controlled more accurately.

COMPARISONDevice Medium Speed in CPSMagnetic Disc UnitMagnetic Tape UnitCOM UnitLaser Page PrinterLine PrinterImpact Character PrinterTelevision MonitorPlotter

Magnetic DiskMagnetic tapeMicrofilm or MicrofichePaperPaperPaperCathode ray tubePaper

100,000 to 2000,000150,000120,00020,000200 to 600050 to 60060 to 2000Not applicable



Computer Hardware IntroductionHard ware is the term used to describe all the actual pieces of equipment in a computer system.Examples of Hardware

1. Peripherals such as input, output and storage devices2. The central processing Unit of a computer3. Input and output media

A computer is a machine which automatically inputs and processes data, and output the result, the actual process carried out is fixed beforehand, usually by a program stored in the machine.Now a days most computers are digital. In practice the quantity used has two states and is often either

1. An electrical voltage usually 0 volts or 5 colts, or2. A magnetic field – in one of two directions

DIGITAL AND ANALOG Analog data - A computer that measures data varying continuously in value, such as speed or temperature.This analog data is continuously variable and digital data is discrete.

DIGITAL COMPUTERPractically all modern computers

1. Are electronic2. Are digital3. Are two-state4. Have a stored program

A typical digital computer system


Output Devices

Backing Store

Input Devices

Control Unit

Main Store Arithmetic and logic

Unit

Central Processing Unit

Flow of Data

Control Signals


The central processing unit (CPU) is the main part of the computer. It Operates at a higher speed than the rest of the computer system and has no moving parts.It is sometimes called central processor and consists of the control unit, the arithmetic and logic unit (ALU) and the main store.The device outside the central processing unit but controlled by it are called peripheral devices or peripherals.Backing Store is a means of storing large amounts of data outside the central processing unit

The Control UnitWhen a compute is running the control unit repeatedly interprets (Decodes) instructions rapidly, one after another. After each instruction is decoded it is carried out (Executed). If the instruction involves a peripheral the control unit signals to operate the peripheral.

Arithmetic and logic unitIf an instruction involves carrying out an arithmetic operation on data, the data is transferred to the arithmetic and logic unit and the operation is carried out there.

Main StoreThe main store of a computer is the fast access store in the central processing unit. It is also called the main memory or the immediate access store The most important function of the main store is to hold programs and data while the programs are being executed.

Characteristics of Main Store1. It can be written to and read from at very high speed. This is done without any

mechanical movement2. It is divided up into small equal sized units called locations. Each location can be

accessed by the computer using a number called its address. Each location has a different address.

3. It is usually consist of two types of store or memoryROM- read only memory, which can be read but not written to andRAM- random access memory, which can be read or written to.

Notes: 1. It is important you use the words location and address accurately. It is not correct

to say that data is stored in an address – it is stored in a location2. Each location may contain as few as 8 bits but often there are 16, 32, or more

The clock



Most digital computers can carry out million or more operations a second. These operations occur in a regular cycle. The changes in the cycle from one state to the next are limited using a pulse produced by a circuit called a CLOCK

MICROCOMPUTER AND MICROPROCESSORIntegrated circuitsAn integrated circuit is a circuit consisting of different electronic components and the connections between them, which has been produced on the surface of a small flat piece of semiconductor material. An integrated circuit is sometimes called an IC.A semi conductor is a substance which conducts electricity but not as well as metals do. The substances usually need for integrated circuits is silicon. A piece of silicon with a circuit on it is called chip.Each integrated circuit is usually encased in a rectangular plastic ‘package’ with two of pins to connect the integrated circuit to other circuit. This connection is usually done by soldering the pins into holes on a printed circuit board.

MICROPROCESSORSA microprocessor is an integrated circuit which contains the control unit, the arithmetic and logic unit and possibly some main store for a computerA microcomputer is a computer for which the main processing is done by microprocessor. Small computers which are not microcomputers are usually called minicomputers. Large powerful computers with a range of peripherals are called mainframe computers.

Dedicated MicroprocessorA dedicated computer is one which is just used for one particular job, Examples are1. A microcomputer can be used to operate the dashboard and some of the controls in a

car. Its task includes:


Micro-processor

Read only memory

Random Access memory

Peripheral Interface

Flow of Data

Control Signals


a. Checking that the seat belts for occupied seats are in use before the engine is started.

b. Monitoring the fuel mixture so that the engine runs economically.2. A camera may contain a microprocessor to control exposure calculations. This may

make it possible to. a. Operate the camera in several different programmed modesb. Select several different points in a picture and have an average exposure

calculated them.



The Central Processing Unit Execution of programs

ProgramsA program is an ordered set of instructions which a computer carries out. The program is stored in the main store while it is being executed. To carry out a task, the control unit fetches and executes the instructions in the correct sequence.Machine code refers to the set of codes which the computer has built in to it. It can decode and execute these without any translation.

Note: A program can be written by a programmer in any programming language.

THE FETCH-EXECUTE CYCLE

The fetch-execute cycle is a timed sequence by which the control unit ‘fetches’ instructions from the main store. They are fetched one at a time and then decoded and executed.

Note: No stop has been shown in the diagram. Usually a computer does not stop fetching and executing instructions while it is switched on, although it does transfer from one program to another.

ExampleWhen a typical microcomputer has finished executing a program which has been ‘RUN’, control is transferred to another program which flashes the cursor on the screen and checks the keyboard to see if a key has been pressedNote: in some processor an instruction may take up to more then one storage location, fetching the instruction will then take two or three operations.

REGISTERSA register is a special-purpose storage location. The computer uses registers for temporary storage of instructions, data and address.


Start

Fetch an instruction from the immediate access store

Decode and execute the instruction

Simplified flowchart of the fetch – execute

cycle




Registers in the control unit1. Program counter – also known as the sequence control register (SCR)

The program counter holds the address of the next instruction to be fetched. As soon as the instruction has been fetched the value in the program counter is increased by 1. As the control unit normally fetches one after another in the order in which they are stored.If the instruction executed causes a branch to an instruction in another part of the program, the value in the program counter is altered to the address of the new instruction.

2. Current instruction registerThe current instruction register holds the instruction fetched from the store while it is being decoded and executed

Registers in the Arithmetic and logic UnitThe registers in the arithmetic and logic unit are involved in the execution of instructionsAccumulatorAn accumulator Register is a register used to store values which are the subject of arithmetic or logical operations or of data transfer

Example1. If two numbers in location A and B are to be added and stored in location C,

instruction with the following function will usually be fetched and executed;a. Load contents of location A into the accumulatorb. Add contents of location B into the accumulatorc. Store contents of accumulator in location C

2. If a character is to be printed outa. A code for the character is loaded into the accumulatorb. The contents of the accumulator are transferred to a buffer ready for

printing.Note: A computer often has more then one accumulator.

TYPICAL INSTRUCTION SET

The instructions set is the set of machine code instructions built into the computerInstructions are need to

1. Transfer data within the computer2. Do arithmetic3. Carry out logical operations4. Branch from one instruction to another in the program

The following examples are written in words. The actual machine code instructions are in binary.

Transfer of data- EXAMPLE1. LOAD ACCUMULATOR- transfer a value into the accumulator2. COPY A B - copy the contents of register A into register B



Arithmetic Example1. ADD A- Add a value to register A2. SUB B – Subtract a value from register B

Logical Operator – Example

1. SHIFT LEFT – shift all the bits in the accumulator 1 place to the left2. ABD A B – do the logical operation and between the contents of A and the contents

of B

Branch InstructionsThese are the instructions used to program the computer to make decisions. Usually the control unit fetches instructions one after another in the order they are stored. However, control can be transferred to another part of the program or to another program. This is done using a branch instruction (also known as jump instruction)A branch instruction is an instruction which causes a jump out of the normal sequence of a program.There are two main types of branch instructions

1. A conditional branch is an instruction which causes a jump only if some condition is met

2. An unconditional branch is an instruction which always causes a jump.

Examples 1. JUMP IF ZERO – jump if the contents of the accumulator is zero (Conditional

Branch)2. JUMP TO SUBROUTINE – jump to a given subroutine (Unconditional)

Typical Instruction formatMany computers have instructions in two main parts.a) Function code b) operand (address)

The function code is a binary code for the actual instructionThe operand is either

1. A data item for the instruction to operate on or2. The address of a location containing a data item

ExampleFor a particular microcomputer each function code takes up eight bitsThe code for LOAD ACCUMULATOR FROM MEMORY is 1010 1001The address of each location takes 16 bitsSo the instruction 1010 1001 0001 1111 1111 1111 means:LOAD ACCUMULATOR with the contents of location 0001 1111 1111 1111

Note: The instruction would probably be displayed in hexadecimal as A9 1FFF



FILES

A file is an organized collection of related recordsA record is a group of related items of data which together can be treated as a unit. The records are usually similar to one another in the type of data they contain and they way they are set out.A field is an area of a record reserved for one particular typed of data. Each field contains one or possibly more, data items.An item of data here means the smallest piece of data that would be dealt with separately a single name or a single number etc.

Examples of files, Records, fields and items

1. Each record of a file of students has the following fields:Surname forename Date of birth AddressOne of the record isWALTERS DAVID ANDREWS 21-02-75 3, BURNSIDE GARDENS, NYThe date of birth field contains the item 21-02-75

2. A payroll file of a firm’s employees, one record would be all the data on one employee, the separate items in a record could include the employee’s a)works numbers, b) name c) tax code, etc.

3. A file stored on the Police National computer giving data on stolen cars. One record would be all the data on one car.The items in a record could include the car’s a) registration number, b) legal owner, c) make, d) color, etc.

4. Any organized collection of data held on backing store, the following can be regarded as files.

a. computer programb. A piece of text stored by a word processor

5. Any organized set of data even if it is not on a computer medium, for example, a set of index cards in an doctor’s surgery. Each record is the data on one patient. The items consist of the patient’s name, history of symptoms and treatment.

Reasons for using files1. In any situations required a permanent source of data which is readily accessible.2. In a computer when the main store is too small for the amount of data being

processed.

FIXED AND VARIABLE LENGTH FIELDSFields may be of fixed length or variable lengthIf the fields are of fixed length then a given field in a record has a set of characters positions reserved for it.If the fields are of variable length, the number of characters in each is not determined beforehand.

Advantages of variable over fixed length



There is no waste of storage space (there is wastage for fixed length fields because a given field has to be as long as the longest item to go in it and space is waste for short items)Advantages of fixed over variable length 1. Computer operations such as searching can be carried out quickly2. Allocation of storage is more straightforward3. Updating of files is simpler- if one record is changed it still takes up the same amount

of space, so that other records do not have to be moved to make room for it.

KEYSUsually one particular field of each record of a file contains an item which is used to identify the record uniquely. This field is called the key field, and the item in it is called the key to that record. In a file the keys must all be different from one another, so that there is no confusion over which record is which

Example illustrating field lengths and keys

1. A stock file for the sales department of a garden centre. The fields are fixed length and are as follows

Field Number of CharactersCatalogue Number 6Name of plant 20Minimum height (Feet) 2Maximum height 2Price (pence) 5Number in stock 3

The key field is catalogue Number and the records are in the order of these keys

002103ABIES GEORGEI 2 3 250 23002104ABIES GEORGEI 3 4 350 14002113ABIES GEORGEI 2 3 250 3002114ABIES LASIOCARPA 3 4 420 6

2. A basic program stored on a floppy disc is an example of a file20 FOR I = 1 to 2030 PRINT N$100 NEXT IHere each record is a line of the program. It has two variable length fields –The line Number and the Basic statement.The key item is the line number and is used by the computer to search for a line when editing or running the program.

ORGANIZATION AND ACCESSThe method of organization of a file refers to



The way in which the records are arranged within the fileThe method of working out where each record is stored in the file

The method of success to files refers to the way in which a program reads from a file or writes data to it.



SEQUETIONAL ACCESSAccess to a file is sequential when records can only be written to or read from it in order, one after another.Sequential files can be stored on either a serial access medium (such as magnetic tape) or a direct access medium (such as magnetic disk)

DIRECT ACCESS (Also Called Random Access)Access to a file is direct when any record can be accessed without having to access other records first.Direct access files can only be stored on a direct access medium (such as magnetic disk)

Advantages of Direct access over sequential1. Selected records can be accessed far more quickly from direct access files.2. Records can be accessed in any chosen order.3. Records do not have to be put into any particular order before the file is created.

Advantages of sequential access over direct1. For the user: sequential files can be stored on most media including magnetic

tape, paper tape and punched cards as well as magnetic disk2. For the programmer: it is usually easier to write programs to handle sequential

files.

FACTORS AFFECTING CHOICE OF METHOD OF ACCESS1. How many records are to be accessed? If records are to be accessed singly or only

a few at a time, then sequential files would be inefficient. Direct access should be used.

2. How large the file is, if a file is small, the time delay in searching it is not important therefore a sequential file is acceptable.

3. Weather the application is interactive, sequential access is often suitable for batch processing. Online applications such as information retrieval usually need direct access.

4. The type of storage medium is being used. If magnetic tape is too used, then files will have to be sequential.

MASTER AND TRANSACTION FILESMaster FileA master file is a files used as a reference for a particular computer application. It may be updated when necessary.Transaction FileA transaction file is a file of temporary data which has been prepared in order to carry out processing operations with the data on a master file. Usually the transaction file is being used to update the mater file.

Example A file holds details of goods stored by a chain of food shops. Each record consist of : product code, name, name of goods, price, minimum number to be held in stock. This file



is the master file.Another file is prepared containing product code and new price for some of the goods on the master file. This is the transaction file and it is used to update the prices on the master file.STORAGE OF FILESFiles on tape are usually stored with extra information both.

Before the first record in a header label, for example file name, date written, etc and after the last record in a trailer label, for example, number of records in the file, etc.Sequential files have an end of file marker, so that programs can reorganize the last record. Disks usually have a directory which is used by the operating system to locate them. A directory is a file containing a list of names of files and the information needed to access those files on the disc.The operating system locates files using an addressing system for the tracks and sectors. This addressing may be built-in at the manufacturing stage or may be added later by formatting the disk. To format a disk means to prepare it for subsequent file storage by adding control information to it. In microcomputers this is usually done by running a program which writes track and sector numbers on the disc. Only blank or unwanted disks should be formatted as the operation will effectively erase any data already on them.

FACILITIES FOR FILE USERS1. Create and access sub directories – a sub directory is a part of the main directory

which can be accessed separately.2. Obtain a catalogue of a given directory -- means list of files in a directory3. (a)save, (b) load, (c) delete. (d) Rename and (e) copy files

(a) To save a file means to copy all the records from the main memory onto a permanent store.

(b) To load a file means to copy all the records from a permanent store into a main store.

(c) When a user deletes a file it can no longer be used. Usually the file is not actually erased from the disk. The reference to it erased from the directory and the space on the disk is made available for other data.

(d) When a user renames a file, the name of it is changed in the directory. The file itself is not altered.

(e) When a file is copied. It is read into the main store. In sections if necessary, and a copy of it is written onto a new disk or another part of the same disk. After the operation there are two identical files, although the user may choose to give the new file a different name.

UPDATINGTo update a file means to alter it with new information . Updating can involve

(a) Adding new record(b) Deleting existing records(c) Changing the items within existing records

Direct access file are sometimes updated one record at a time.



UPDATING A SEQUENTIAL TAPE FILE1. A transaction file is prepared containing all the updating information. It contains

details of all records which are to be added, deleted or changed.The records on this are in the same order as the records on the master file. This is done by having both files arranged with their keys in ascending order.

Note: the files are arranged with their keys in the same order because otherwise the updating would take an impractically long time and involve much winding and rewinding of tapes.

2. An updating program is run which reads the master file and the transaction file one record at a time. At the same time a new, updated master file is written; the old master file is not changed.Note. The old master file is not changed because

a. It is not practical to try to insert, change or delete records on a existing sequential file, practically on tape.

b. The old master file can still be useful for security purpose.

SEARCHING, MERGING AND SORTING

SEARCHINGTo search a file means scan it methodically looking for a given item. The simplest method of searching is a linear search. A linear search is one in which each record is read in turn and checked for the item. If the end of the file is reached without finding the required item the search was failed.Word processor and editor programs allow the user to search for a word in a passage of text and to replace it with another word if necessary.


Transaction File

Updating Program

Master file

New Mater File


File enquiry package are available which allow the user to search a file for items or combinations or selected items

ExampleThe following is part of a detailing the name and colorings of cat breeds

Name Color1 Color2 Color3 EyesBirman Blue Chocolate BlueBlue-cream long-hair Blue Cream OrangeBlue Persian Blue OrangeBritish blue Blue OrangeBrown Burmese Brown YellowCilico Black Red Cream OrangeChinchilla White GreenHavana brown Brown Green

An enquiry program is used to file the names of cats with certain color combinationsa. The search pattern: color 1= Brown

Produces the name : Brown Burmese, Havana brownb. The search pattern: (color 2= Cream OR color 3 = Cream) and (Eyes = orange)

Produces the name : Blue-cream long-hair , Cilico

MERGINGTwo files are merged by interleaving their records to form one file which still has its records in order.A common example of merging is when two sequential files have their records in order and they have to be combined into a single file

Example of mergingA firm selling car parts has a master file of all the stock. Detail of each part are stored in one record with the part number as key item. The file is stored sequentially in the order of the part numbers. When a new car model is introduced a file detailing all its parts is supplied to the firm. This is then merged with the existing master file to produce a new file which includes parts for the new car.

SORTING To sort data means to arrange it into order. Usually alphabetical data is sorted into alphabetical order and numbers into ascending order.Files are sorted because;1. File operations on two or more files are simpler if the files are in the same order 2. An operation on a serial file may be easier if the keys are in order3. People reading files printed out on paper find them easier to use if they are in order.

WORKED QUESTIONS



For the two file A and B, the first item of each record is to be taken as the key by which they are sequenced. The files are.

FILE A256023 A.F. SMITH 234.56403214 J.P.JONES 156.25207888 L.C.JACKSON 2478.00365142 P.JONES 89.50

FILE B864512 P.R.TAYLOR 105.23956421 A.FREEMAN 325.20125642 S.ARBER 1025.60320147 P.R.WEBER 68.25403215 M.PALMER 512.00

Show the Results of1. Sorting the two files into correct sequence,2. Merging the sorted files

1. File A when sorted is207888 L.C.JACKSON 2478.00256023 A.F. SMITH 234.56365142 P.JONES 89.50403214 J.P.JONES 156.25

125642 S.ARBER 1025.60320147 P.R.WEBER 68.25403215 M.PALMER 512.00864512 P.R.TAYLOR 105.23956421 A.FREEMAN 325.20

2. The two files when merged 125642 S.ARBER 1025.60207888 L.C.JACKSON 2478.00256023 A.F. SMITH 234.56320147 P.R.WEBER 68.25365142 P.JONES 89.50403214 J.P.JONES 156.25403215 M.PALMER 512.00864512 P.R.TAYLOR 105.23956421 A.FREEMAN 325.20

SORTING SEQUENTIAL FILES In a computer, data can only be sorted when it is in the main store. Usually a file is too large to store all at once in the main store.Such a file can be sorted as follow:



1. The file is read into the main store, a group of records at a time2. Each group is sorted and written back onto the backing store3. When all the group have been sorted, they are merged again to produce a completely

sorted file

METHODS OF SORTING DATA IN THE MAIN STOREA set of data items can sorted into order by many methods. The methods below have been described for numbers, but can also be used to sort names and other strings.

InsertionBuild up a new set of numbers by taking each number in turn and inserting it into its correct place in the new set.

SelectionSearch through the set, select the smallest and place it first. Then search again to find the next smallest, place it second and so on until they have all been selected.

Exchange1. Compare two of the numbers to see if they are in the correct order.2. If they are, leave them alone; if not, exchange them.3. Carry on until all the numbers are in the correct order

BUBBLE SORTA bubble sort is an exchange sort in which a number is always compared for possible exchange with the one next to it in the set.
