Polling, Spooling and Interrupt in Operating System

1.     Polling:

Polling is a process in which Operating System continuously integrates if any peripheral needs attention of OS.

2.     Interrupts:

An interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. An interrupt alerts the processor to a high-priority condition requiring the interruption of the current code the processor is executing (the current thread).

3.     Spooling:

Acronym for simultaneous peripheral operations on-line, spooling refers to putting jobs in a buffer, a special area in memory or on a disk where a device can access them when it is ready. Spooling is useful because devices access data at different rates. The buffer provides a waiting station where data can rest while the slower device catches up.

The most common spooling application is print spooling. In print spooling, documents are loaded into a buffer (usually an area on a disk), and then the printer pulls them off the buffer at its own rate. Because the documents are in a buffer where they can be accessed by the printer, you can perform other operations on the computer while the printing takes place in the background. Spooling also lets you place a number of print jobs on a queue instead of waiting for each one to finish before specifying the next one.

Read More

Data Protection Act 1998

The Data Protection Act 1998 sets out rules for processing personal information, and it applies to some paper records as well as those held on computer and some automatically processed data, for example, document image processing, audio/video, photographs and CCTV. The Act gives individuals certain rights, and imposes obligations on those who record and use personal information to be open about how information is used and to follow eight data protection principles:

Data Protection Principles
Personal data must be processed following these principles so that data are:

1. processed fairly and lawfully
2. obtained for specified and lawful purposes
3. adequate, relevant and not excessive
4. accurate and, where necessary, kept up-to-date
5. not kept for longer than necessary
6. processed in accordance with the subject's rights
7. kept secure
8. not transferred abroad without adequate protection

Rights of Data Subject (individuals) under the Act
The Data Protection Act 1998 came into force on March 1 2000. The Act gives legal rights to individuals in respect of personal data held about them by others.

Under the Act, personal data must be processed following the Data Protection Principles so that data are:

1. processed fairly and lawfully and only if certain conditions are met
2. obtained for specified and lawful purposes
3. adequate, relevant and not excessive
4. accurate and where necessary kept up-to-date
5. not be kept for longer than necessary
6. processed in accordance with the rights of data subjects
7. kept secure
8. not be transferred abroad unless to countries with adequate data protection laws

You are entitled to have access to information held about you, except where releasing that information would breach another person's privacy. You also have rights including rights to prevent processing likely to cause unwarrented damage or distress and to prevent processing for the purposes of direct marketing.

Read More

Tackling the exam papers (Exemple candidate response)

Tackling the exam papers

General tips

In many cases, you can find clues about the answer within the question itself. The main 'clues' are:

•       the number of marks given for the question

•       the key instruction words e.g. Name, Describe, Compare, Evaluate ...

•       instruction/question text written in bold typeface.

The number of marks

The number of marks awarded for a question is given in square brackets [ ] after each question or subpart of a question. Typically (though not always), the number of marks gives an indication of how many different points you need to make. For example:

Explain what is meant by top-down design                                                                               [2]

There are potentially 5 or 6 different points you could make to answer this question successfully. However, as it is only worth 2 marks, the examiner is most likely only looking for any 2 correct comments. You could spend 20 minutes writing 6 accurate comments but you would still only score 2 marks because this is the maximum allowance for the question.

You won't lose marks for writing extra answers, but you could waste time writing points that won't score you any more marks. Also, the examiner might decide to only look at the first 2 points and ignore the rest. So, make sure you always put the answers you are certain are correct first before any additional answers.

The number of marks indicates the likely number of separate points you need to make and it is also a good indicator of how much time you should spend on that particular question. For example, it is more sensible to spend much longer writing the answer to a question worth 5 marks than one worth 1 mark. BUT this is not always the case. For some questions the number of marks does not indicate how many comments you need to make. So, you should always take the time to think about the questions and your answer before committing pen to paper.

Key instruction words

The examination questions will oft en have a single word that tells you how much detail is required for each answer. Typically, the following is true:

•       State, Name, List means that all you have to do is give the name of what is being asked for.

•       Describe, Explain means you should say how something works (this will depend on the actual question, it might not always be how but it infers more detail than simply listing a name).

•       Compare means you should say how both things work and sometimes what are the differences between them.

•       Evaluate means you should say how well or poorly the object/method/application etc. works, or how suitable something is for a given scenario.

•       Justify means you should say why the object/method/application etc. has been chosen.

Think about what each of these words is asking for in the question. This can really help you write a good answer.

Instruction text written in bold or capitals

This applies to general text within the instruction/question as well as the key instruction words mentioned above. When certain text is given in bold or sometimes CAPITALS it is meant to draw your attention to it and emphasise its meaning.

Often a question will ask you to give 'two examples of ' where the word 'two' is written in bold typeface. This means that you have to supply at least two examples in order to get the marks even if the answer is only worth 1 mark! In other words, it is a clue to the minimum number of different points you need to make regardless of the number of marks. Similarly, if the question included the instruction to 'Evaluate' it means that you have to do more than simply state the name of a term. You have to also discuss its advantages and disadvantages, for example. In such cases, you are being given a direct and clear instruction and you must follow it in order to get the marks.

Examination technique

An hour of revision the night before the examination is a good idea. It is not a good idea to cram in as much revision as possible at the last minute by spending hours revising the night before; or to stay up into the early hours of the next morning.

What you really need to do is:

•       get a good night's sleep and relax in order to be in a positive frame of mind

•       make sure you have the correct equipment (remember to take spare pens)

•       when you get to the examination room:

o    arrange your equipment on the desk and relax

o    before you write anything, quickly read through all the questions on the examination paper, the last question is not always the hardest

o    start by answering a couple of the easier questions to boost your confidence, then tackle the more difficult questions

o    an alternative would be to answer the questions in increasing level of difficulty so that you leave the more difficult questions until the end

o    remember to keep an eye on the time, don't spend too long on any one question, even if you know everything there is to know on that particular topic. The question paper will usually tell you how many marks there are for each question and so you can use this to work out how much time to spend on each question.

o    in cases where you have to write in the answer, make sure that you answer every question even if you are having to guess. You cannot score marks if you don't give an answer, but an educated guess could end up scoring you marks.

Make sure you take whatever approach works for you. We are all different and work in different ways.

Above all, READ THE QUESTION.

Exemple candidate response

Question 1 (a)

Define the terms:

(i) hardware

(ii) software

Mark scheme

(i) – The physical/electronic parts of a computer system

Parts you can see/touch no mark

(ii) – Sequence of instructions/programs [2]

Example candidate response – grade A

Examiner comment

This candidate response was clear and precise. In both parts of the question the definitions were almost straight from the text book. A very good answer.

Example candidate response – grade C

Examiner comment

There was some idea that hardware are the physical parts of the computer, but the candidate struggled to define software to an adequate standard. This is a noticeably weaker response than a grade A candidate.

Example candidate response – grade E

Examiner comment

Grade E candidates usually got one part of the definition correct; it was rare to see both parts answered correctly. There is evidence that actual definitions had not been learnt and the candidate was trying to do the description from memory or experience.

Question 1(b)

A supermarket has a number of point-of-sale terminals.

Data is read from goods at the terminals and information is produced.

State two output devices which would be used at the point-of-sale, justifying their use.

Mark scheme

– Printer/to print till receipt

– Beeper/to indicate correctly read barcode/error reading barcode

Speakers/to give instructions to customer

– LED/LCD screen to show information about purchase

(2 per –, max 4) [4]

Example candidate response – grade A

Examiner comment

Two good examples of output devices were given in this answer (monitor and printer). The choices were very clearly justified by the candidate. The answer was further expanded indicating a clear and deep understanding of peripheral devices and the reasons why a device would be chosen for a given application.

Example candidate response – grade C

Examiner comment

There was little difference between grade A answers and grade C answers in this question. The main difference being the lack of additional information in the answer when compared to an grade A candidate; but enough was usually done to get full marks.

Example candidate response – grade E

Examiner comment

In this candidate's response there is obvious confusion between output devices and input devices. In this case, a barcode reader has been chosen as an output device.

Question 1 (c)

State three types of output needed at the point-of-sale terminals. For each type of output explain why the output is needed.

Mark scheme

– Sound/indicates barcode properly read without operator diverting attention from job

– sound to indicate terminal is free

– Video image or screen output or soft copy/to allow shopper to check goods and prices as they are input to system

– Receipt or printout or hard copy/to allow shopper to check payments and shopping at home, proof of purchases.

(2 per –, max 6) [6]

Example candidate response – grade A

Examiner comment

Three good choices were given which were clearly correct types of output. The reasons for type of output were well laid out and referred correctly to the application in the question.

Example candidate response – grade C

Examiner comment

The candidate correctly knows that the question required output types and gave audio (in the form of a beeping sound), then found it difficult to distinguish between output device and type of output, and came up with the answers 'graphs' and 'texts'. Both of these were throw away answers. It is common at grade C level for candidates not to understand the subtle difference between output device and the output produced by a device.

Example candidate response – grade E

Examiner comment

A typical grade E candidate finds it difficult to distinguish between output devices and output types. This candidate's answer was typical of the confusion; although they did suggest a 'print out' which gained them a mark.

Question 1 (d) (i)

The management of the supermarket use a number of different types of software.

State what each of the following types of software would be used for.

Give a feature of each which makes it suitable for your use.

(i) Desktop publishing (DTP)

Mark scheme

– Producing leaflets/flyers/brochures/posters

– Using frames to divide up content/editing features/...

– combining images and text [2]

Example candidate response – grade A

Examiner comment

In this response there was good use of DTP i.e. producing leaflets; but the candidate expanded the answer to indicate why the supermarket would produce leaflets. It produced a very good, comprehensive answer. The features of DTP were clearly understood and distinguished it from other software such as word processors i.e. wrap text around graphics and make complex page layouts.

Example candidate response – grade C

Examiner comment

The candidate obviously knows what DTP can be used for but found it difficult to explain what features make this software suitable for the task chosen. It was very common among grade C candidates to find it difficult describing the features of DTP.

Example candidate response – grade E

Examiner comment

Frequently at this level, use of features were confused or combined together. A mark was frequently gained for, e.g. leaflets, but generally little or no idea about software features.

Read More

2 Data (Computer Science)

Data and information

Data are the raw facts and figures that we give to a computer as input. Data lack sufficient context and processing to have meaning.

When data are processed to have context and meaning, and to search, sort and make calculations, they become known as 'information'.

Data collection and preparation

Data may need preparation after collection and before they are used as an input, to ensure that they are in the correct format.

Data are encoded to summarise them, so that they are quicker to enter, with fewer errors, occupy less memory and backing storage, and are quicker to process.

Data sometimes need to be prepared so that they have a uniform format suitable for input into a computer.

Analogue-to-digital converters and digital-to-analogue converters

An analogue input signal needs to be converted into digital data. This is done with an analogue-to-digital converter (ADC). This process is known as digitisation.

 

Digital output signals often need conversion to analogue signals in order to provide an output. This is done with a digital-to-analogue converter (DAC).

ADC and DAC devices can be found in a computer's sound card.

Data capture and checking

Data capture is when data actually enters the computer. This happens after data collection and data preparation. Data capture may be:

•  Manual

•  Automatic.

Inaccurate data are of little value, so their accuracy is checked by validation and verification.

Data validation

A validation check prevents the input of a data item if it is not sensible and reasonable. When this is the case, an error message is displayed. Types of validation check include:

•       Type

•       Range

•       Limit

•       Length

•       Character

•       Format Or Picture

•       Presence

•       Consistency

•       Check Digit.

 

Data verification

Verification is a way of preventing errors when data is copied from one medium to another (e.g. from paper to disk/CD, from memory to DVD, etc.). There are a number of ways in which verification can be done:

Double entry in this method, data is entered twice (using two different people); the data is only accepted if both versions match up. Often used to verify passwords by asking them to be typed in again by the same person.

Visual check this is checking for errors by comparing entered data with the original document (NOTE: this is not the same as proof reading!!).

Parity check this is used to check data following potential transmission errors; an extra bit is added to each binary number before transmission – e.g. EVEN parity makes sure each number has an even number of 1 – bits;

Example: if 11000110 is sent (four 1's)  and 11100110 is received (five 1's)  then the system will know an error has occurred.

File organisation and manipulation

–      a record is a set of data usually displayed in a row of a table:

–      a data field holds a specific type of data about a characteristic of the items recorded, usually displayed in a column of a table

–      a record key field holds a unique identifier for each record

–      a set of records are stored together as a data file

•  records within files can be organised in different ways:

Ø  A Serial file:  A File in which data is stored in the order in which it arrives.

Ø  A Sequential file: A file in which data is stored in a sequence using a key field and can be read from beginning to end.

Ø  A Direct access file: A file stores data in no particular order and is very useful because adding new data is very simple in it.

File maintenance

File maintenance is the processing of a file that is not part of routine transaction processing, or updating a main file using a transaction file. Maintenance involves:

•  inserting a record, e.g. a new record for a new client

•  deleting a record, e.g. removing the record of a client who ends their relationship with the organisation

•  updating (amending or editing) a record, e.g. altering the record of a client who changes  their address.

This usually involves rewriting the whole file for a sequential file, but not for a direct access file.

Data types

Different data types are identified so that a computer can store and process the data appropriately.

Data types include:

Ø  string (or text)

Ø  number (numeric):

o    integer

o    real (or decimal)

Ø  currency

Ø  date/time

Ø  Boolean (or Yes/No).

Data structures are more complex data types, consisting of a number of data items of one or more data types. They include the record and array structures.

An array consists of a number of elements of a single data type. An array may have one or more dimensions. A program refers to an element using the array's identifier and an index number for each dimension. This approach enables efficient programs for filling an array, searching for a value in the array or generating output from its elements.

Binary Data

Controlled devices usually contain registers which are made up of binary digits (bits). The following example shows how these registers can be used to control a device.

(1 = ON and 0 = OFF)

Therefore, 1 0 1 0 1 0 1 0

means:

front wheel turns left

back wheels turn left

the direction is forward

the motors are on

therefore the trolley is moving forward and turning left.

(i) What does this register mean?

0 0 0 1 0 1 1 1 ?

(ii) How would the following be represented using the above register?

- front wheel turning right

- back wheels turning left

- moving in a forward direction

- motors on

- no object in its path

Answers

(i) - front wheel not turning left or right

- rear wheels turning right

- going in backward direction

- motors on

- error – object in path

So the vehicle is going nowhere.

(ii) 0 1 1 0 1 0 1 0

 

Questions:

4. An estate agent uses a computer system to store details about properties for sale. A section of the properties file is shown below:

1.  Why is coded data used for Type?
2. What is the data type for Price?
3.  What is meant by a key field? Which is the key field?

5. a  What is meant by analogue data?

2.  When does analogue data need to be changed into digital data?
3.  What device performs the conversion?
4. Give one application which would use analogue data.

6.  a   What is meant by digital data?

2. Give one application which would use digital data.

7.  Explain the following terms:

a.     database

b.    file

c.     direct access file

d.    record

e.     sequential file.

8.  A shop sells bicycles. Information about each bicycle in stock is held in a computer file. Part of the information is shown in the table below.

a.     How many fields are shown?

b.    How many records are shown?

c.     Give a reason why the shop would need to delete a record from the bicycle stock file.

d.    Give a reason why the shop would need to add a record to the bicycle stock file.

e.     Explain how the shop can print a list of mountain bikes.

f.     There is an error in the table. Which item is wrong? How could this error have been avoided?

g.    Which is the key field?

9.  A video club hires films to members. The club uses separate database files to store details about films, members and the films hired.

a.     Name four suitable items of information for the FilmsHired  database file, specify the field type and give an example of the data.

b.    Name four suitable items of information for the Members database file, specify the field type and give an example of data.

10. a   What is meant by the term 'validation'?

2. What is meant by the term 'verification'?
3. Describe one method of verification when changing a password.

Answers:

Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers.

2 A file is a collection of related data such as a set of data records. A record is a data structure that contains items of data about a thing in the real world. Each item of data within a record is known as a field.

3 a Coded data is used for Type because the full description would be longer. It would take up more storage space and may lead to errors in data entry.

b The data type for Price is real or decimal (numerical data type).

c A key field is an item of data that uniquely identifies a record. In this case, the key field is Property.

4 a Analogue data is data that changes continuously rather than in discrete jumps, for example, temperature or volume. It can be captured by a sensor.

b Analogue data need to be changed into digital data for it to be manipulated by a computer.

c An analogue-to-digital converter performs the conversion.

d A greenhouse control application would collect analogue temperature data and a computer would decide when to switch on and off a heater.

5 a Digital data is data that changes in discrete, or stepwise, jumps. For example, the number of bikes sold or a person's age.

b A utility billing application would use digital data from meter readings.

6 a A database is a set of tables that hold information about related things. (See page 8 or glossary.)

b A file is a set of data or program items held in a named area of storage (or a physical data structure).

c A direct access file is a file stored on disk. Its records can be accessed directly by using an algorithm to generate a record's disk address from the record's key value.

d A record is a set of data items about one type of thing.

e A sequential file is a file in which records are stored in order of their record key values.

7 a There are six fields (columns) shown. (See page 9 or glossary for definition of a 'field'.)

b There are seven records (rows) shown.

c The shop would need to delete a record when a bicycle is sold.

d The shop would need to add a record when a new bicycle is delivered from the supplier.

e The shop can print a list of mountain bikes by selecting all records where the Type = 'Mountain'.

f The price of stock number 1972 is incorrect. It could have been avoided by setting a limit or range.

g The key field is StockNo.

8 A video club hires films to members.

a Four suitable items of information for the FilmsHired file are:

b Four suitable items of information for the Members file are:

9 a The term 'validation' means examining input data to ensure that it falls within pre-set criteria. For example, a date of birth must be before a certain date to be valid for a pupil to be enrolled.

b The term 'verification' means double-checking that copied data is correct.

c One method of verification when changing a password is to ask the user to type it a second time, i.e. double entry.

Examination Based Questions:

A list of examination-based problems now follows. These can be used as revision questions or centres can use the questions to make up their own assessments to give candidates practice under examination conditions.

(1) Describe four methods used for automatic data capture. Give a different application for each of the methods chosen.

(2) A record contains the following fields:

- Title (Mr/Mrs/Miss) and Sex (Male or Female)

- Date of birth (written in the form dd/mm/yyyy)

- Pay Number (which is made up of 8 digits)

- Telephone Number

- Pay

Give a different validation check for each of the above fields and explain why it is used.

(3) A system uses the ISBN-10 (modulo 11) method to generate and validate bar codes:

- each digit in the number is multiplied by its digit position

- the result of each multiplication is added to a total

- the total is then divided by 11

- the remainder is subtracted from 11 to give the check digit (if the remainder is 10, the letter "X" is used as the check digit)

(a) Which of the following numbers have the correct check digit?

(i) 0 – 5 5 5 – 2 1 6 2 2 – 5

(ii) 0 – 1 2 1 – 9 0 0 2 1 – X

(b) Calculate the check digit for the following number:

0 – 1 5 0 – 2 4 6 2 2 – ………

(c) Discuss the types of errors that check digits can identify.

(4) (a) Describe three ways of carrying out verification checks.

(b) Give two examples where verification checks would be made.

(5) A burglar alarm system uses an 8 – bit register. The first 4 bits indicate if a sensor has picked up an intruder (shown with a 1 – value) and the second four bits indicate the zone where the sensor has picked up an intruder:

(b) What would be the binary pattern for a window broken and an infra red sensor detecting an intruder both in zone 15?

(6) A company is using a word processor to produce a page advertising their products. Unfortunately, the information wouldn't fit onto one single page.

Which five features of a word processor could be used to ensure that the advert fits onto one page only.

(7) A college has invested in a computer system to help carry out the following tasks:

- advertise their college (both on the Internet and by paper leaflets)

- keep a track of student and staff information/contact details

- keep a track of payments and fees

- produce on line courses for the students

Describe four software packages the college could use to carry out the above tasks and explain why each software package has been chosen.

(8) Describe three fundamental differences between word processors and desk top publishing packages.

 (9) A database has been set up to compare certain features of freezers. A section of the database is shown below.

(a) How may records are shown in this section of the database?

(b) What items would be output if the following search condition was input:

(Price($) > 300 OR Warranty(years) > 1) AND (Colour = "silver") ?

(c) Give the search condition to find all freezers which operate below - 25⁰C and have a capacity of more than 0.25 m³.

 

Bit Pattern Exam Questions

 

Specimen 2015 P1 (Q4)

A digital alarm clock is controlled by a microprocessor. It uses the 24-hour clock system (i.e. 6 pm is 18:00). Each digit in a typical display is represented by a 4-digit binary code.

(c) The clock alarm has been set at 08:00.

Describe the actions of the microprocessor which enable the alarm to sound at 08:00.     [2]

Marking:

 (c) Any two from:

– microprocessor compares present time with stored time

– if the values are the same

– sends signal to sound alarm [2]

Specimen 2015 P1 (Q13)

When a key is pressed on the keyboard, the computer stores the ASCII representation of the character typed into main memory. The ASCII representation for A is 65 (denary), for B is 66 (denary), etc.

There are two letters stored in the following memory locations:

(a) (i) Show the contents of Location 1 and Location 2 as binary.

Location 1, Location 2                                                                                                   [2]

(ii) Show the contents of Location 1 and Location 2 as hexadecimal.

Location 1, Location 2 [2]

(b) The following machine code instruction is stored in a location of main memory:

Convert this binary pattern into hexadecimal.                                                                              [4]

(c) Explain why a programmer would prefer to see the contents of the locations displayed as hexadecimal rather than binary, when debugging his program that reads the key presses.            [2]

Marking Scheme:

 (c) – easier to identify values

– easier to spot errors [2]

Summer 2013 P13 (Question 14)

14 Some decorative lights are made up from a cluster of red, blue, green, yellow and white LEDs.

Each colour is represented by a binary code:

A 6-bit register, R1, stores the 1-values to represent a sequence of colours.

Thus, if R1 contains:

this means the blue, yellow and black colour sequence is stored and displayed in that order.

The length of time each light is on is set by a binary value in another register, R2: Thus

means each colour is on for 2 seconds.

(a) The two registers contain the following values. What is the sequence of coloured lights and the timing for each colour?

Summer 2007 P1 (Question 9)

A 7-segment display is used to indicate which floor a lift is on. Each segment is numbered as shown:

A byte is used to hold the data needed to light the correct segments. Bit 0 is always zero.

For example, 3 is represented by

(a) If the lift is to stop at more than one floor, the data is held in successive bytes. For example:

Which floor numbers are stored in each byte?

First byte floor number

Second byte floor number [2]

(b) What bit pattern is used to indicate Floor 2?

(c) The lift is travelling down to stop at Floors 5, 3 and 1. When it stops at Floor 5, a passenger gets in and presses the button for Floor 2.

How does the system ensure that the lift stops at Floors 3, 2 and 1 in that order?   [3]

Summer 2005 (Question 8)

A microprocessor controls the washing cycle of an automatic washing machine and gives output to the following devices:

• water valve                 • heater                         • wash motor                 • pump

Control bits are sent to turn parts of the system on or off, i.e. 1 is on and 0 is off.

(a) State what is happening when the above bit pattern is set.

.....................................................................................................................................[1]

(b) Write down the bit pattern that would be set if the water has reached the correct level, the temperature is the required temperature, the clothes have been washed and the pump is now pumping the water out of the machine.

(c) State one other process that the microprocessor could control.

.....................................................................................................................................[1]

Winter 2003 (Question 12)

Two 7 segment displays are used on a car dashboard to give information to the driver. Each segment is numbered as shown.

For example, the information 1P shown above is represented by:

Bit 0 is always zero

(a) What is being displayed to the driver if bytes (1) and (2) are showing?

(b) What bit patterns must be used to show the information 0L?

(c) Most of the other information on the dashboard is in analogue form.

(i) State one advantage of displaying information in analogue form.

..................................................................................................................................

...............................................................................................................................1]

(ii) State one disadvantage of displaying information in analogue form.

..................................................................................................................................

...............................................................................................................................1]

 

Data are the raw facts and figures that we give to a computer as input. Data lack sufficient context and processing to have meaning.

When data are processed to have context and meaning, and to search, sort and make calculations, they become known as 'information'.

Data collection and preparation

Data may need preparation after collection and before they are used as an input, to ensure that they are in the correct format.

Data are encoded to summarise them, so that they are quicker to enter, with fewer errors, occupy less memory and backing storage, and are quicker to process.

Data sometimes need to be prepared so that they have a uniform format suitable for input into a computer.

Analogue-to-digital converters and digital-to-analogue converters

An analogue input signal needs to be converted into digital data. This is done with an analogue-to-digital converter (ADC). This process is known as digitisation.

 

Digital output signals often need conversion to analogue signals in order to provide an output. This is done with a digital-to-analogue converter (DAC).

ADC and DAC devices can be found in a computer's sound card.

 

Data capture and checking

Data capture is when data actually enters the computer. This happens after data collection and data preparation. Data capture may be:

•  manual

•  automatic.

Inaccurate data are of little value, so their accuracy is checked by validation and verification.

Data validation

A validation check prevents the input of a data item if it is not sensible and reasonable. When this is the case, an error message is displayed. Types of validation check include:

•  type

•  range

•  limit

•  length

•  character

•  format or picture

•  presence

•  consistency

•  check digit.

 

Data verification

Sometimes an inaccurate data item can pass validation checks due to a copying error. Verification is a way of double-checking to ensure that data remain accurate when they are copied. Common checks are:

•  visual

•  double entry

•  parity bit.

File organisation and manipulation

•  a record is a set of data usually displayed in a row of a table:

  – a data field holds a specific type of data about a characteristic of the items recorded, usually displayed in a column of a table

  – a record key field holds a unique identifier for each record

  – a set of records are stored together as a data file

•  records within files can be organised in different ways:

  – a serial file

  – a sequential file

  – a direct access file.

 

File maintenance

File maintenance is the processing of a file that is not part of routine transaction processing, or updating a main file using a transaction file. Maintenance involves:

•  inserting a record, e.g. a new record for a new client

•  deleting a record, e.g. removing the record of a client who ends their relationship with

the organisation

•  updating (amending or editing) a record, e.g. altering the record of a client who changes their address.

This usually involves rewriting the whole file for a sequential file, but not for a direct access file.

Data types

Different data types are identified so that a computer can store and process the data appropriately.

Data types include:

•  string (or text)

•  number (numeric):

  – integer

  – real (or decimal)

•  currency

•  date/time

•  Boolean (or Yes/No).

Data structures are more complex data types, consisting of a number of data items of one or more data types. They include the record and array structures.

An array consists of a number of elements of a single data type. An array may have one or more dimensions. A program refers to an element using the array's identifier and an index number for each dimension. This approach enables efficient programs for filling an array, searching for a value in the array or generating output from its elements.

 

Questions:

1   A shop has four students delivering newspapers to its customers. Each student delivers three different papers (RECORDER, MAIL and ARGUS). The shop manager uses a spreadsheet to record the deliveries as shown below:

 

2   The terms  file,  record  and  field  are used in databases. Explain the meaning of each term and explain the connections between them; you may wish to include a diagram.

3   An estate agent uses a computer system to store details about properties for sale. A section of the properties file is shown below:

a  Why is coded data used for Type?

b  What is the data type for Price ?

c  What is meant by a key field? Which is the key field?

4  a  What is meant by analogue data?

b  When does analogue data need to be changed into digital data?

c  What device performs the conversion?

d  Give one application which would use analogue data.

 

5 a   What is meant by digital data?

b  Give one application which would use digital data.

6  Explain the following terms:

a  database

b  file

c  direct access file

d  record

e  sequential file.

7  A shop sells bicycles. Information about each bicycle in stock is held in a computer file. Part of the information is shown in the table below.

 

a  How many fields are shown?

b  How many records are shown?

c  Give a reason why the shop would need to delete a record from the bicycle stock file.

d  Give a reason why the shop would need to add a record to the bicycle stock file.

e  Explain how the shop can print a list of mountain bikes.

f  There is an error in the table. Which item is wrong? How could this error have been avoided?

g  Which is the key field?

8  A video club hires films to members. The club uses separate database files to store details about films, members and the films hired.

a  Name four suitable items of information for the FilmsHired  database file, specify the field type and give an example of the data.

b  Name four suitable items of information for the Members database file, specify the field type and give an example of data.

9 a   What is meant by the term 'validation'?

b  What is meant by the term 'verification'?

c  Describe one method of verification when changing a password.

 

Answers:

Below each answer there is a page reference for the coursebook. This is there to help you focus

your revision. If you find that you get an answer wrong, you can use this guide to return to the

coursebook to revise the areas that need some extra attention. Please note these are example

answers only and do not represent the only possible answers.

1 The data type in cell:

a A2 is text.

b D3 is number (or integer).

c E5 is Boolean (Yes/No).

2 A file is a collection of related data such as a set of data records. A record is a data structure

that contains items of data about a thing in the real world. Each item of data within a record is

known as a field.

3 a Coded data is used for Type because the full description would be longer. It would take up more storage space and may lead to errors in data entry.

b The data type for Price is real or decimal (numerical data type).

c A key field is an item of data that uniquely identifies a record. In this case, the key field is Property.

4 a Analogue data is data that changes continuously rather than in discrete jumps, for example, temperature or volume. It can be captured by a sensor.

b Analogue data need to be changed into digital data for it to be manipulated by a computer.

c An analogue-to-digital converter performs the conversion.

d A greenhouse control application would collect analogue temperature data and a computer would decide when to switch on and off a heater.

5 a Digital data is data that changes in discrete, or stepwise, jumps. For example, the number of bikes sold or a person's age.

b A utility billing application would use digital data from meter readings.

6 a A database is a set of tables that hold information about related things. (See glossary.)

b A file is a set of data or program items held in a named area of storage (or a physical data structure).

c A direct access file is a file stored on disk. Its records can be accessed directly by using an algorithm to generate a record's disk address from the record's key value.

d A record is a set of data items about one type of thing.

e A sequential file is a file in which records are stored in order of their record key values.

7 a There are six fields (columns) shown. (See page 9 or glossary for definition of a 'field'.)

b There are seven records (rows) shown.

c The shop would need to delete a record when a bicycle is sold.

d The shop would need to add a record when a new bicycle is delivered from the supplier.

e The shop can print a list of mountain bikes by selecting all records where the Type = 'Mountain'.

f The price of stock number 1972 is incorrect. It could have been avoided by setting a limit or range.

g The key field is StockNo.

8 A video club hires films to members.

a Four suitable items of information for the FilmsHired file are:

b Four suitable items of information for the Members file are:

9 a The term 'validation' means examining input data to ensure that it falls within pre-set criteria. For example, a date of birth must be before a certain date to be valid for a pupil to be enrolled.

b The term 'verification' means double-checking that copied data is correct.

c One method of verification when changing a password is to ask the user to type it a second time, i.e. double entry.

Examination Questions

Summer 2010 P11;

Q15) A database has been set up to bring together information about the world's tallest buildings. A section of the database is shown below.

(a) How many records are in the section of the database shown?                                        [1]

(b) Using Ref No. only, which records would be output if the following search condition was  entered:

(Year < 1990) AND (Height (m) > 375)?                                                                                [1]

(c) Write down a search condition to find out how many buildings are in China or how many buildings have more than 80 floors.                                                                                     [2]

(d) For each of the following fields give a different validation check.                                   

Year

Ref No.                                                                                                                                   [2]

(e) The database was sorted in descending order of Year. Using Ref No. only, write down the results of the sort.                                                                                                                        [1]

Summer 2010 P12

Q 7) A screen has been developed to allow the input of data into the following fields:

name, sex, address, date of birth and examination results.

(a) A first attempt at designing the screen is shown below:

 

This is not a very good input screen. Give four ways in which it could be improved.

1

2

3

4                                                                                                                                              [4]

(b) (i) What is verification?

(ii) Which fields should be verified?                                                                                        [3]

Q 11) A database has been set up showing information about cars:

(a) Using Car ref only, write down which cars would be output if the following search condition was used:

(No of doors = 4) AND (Fuel used (km/litre) > 15)                                                                [2]

(b) Write down a search condition to find out which cars have engines larger than 1.8 litres OR have CO2 emissions higher than 150 g/km.                                                                         [2]

(c) The database is sorted in ascending order on Fuel used (km/litre). Using Car ref only, write down the results of the sort.                                                                                                           [2]

 

 

 

Marking Scheme

 

Summer 2010 P12

Q 7 (a) Any four improvements from:

– use (text) boxes for

– names

– addresses

– sex

– date of birth

– subjects

– grades

– separate fields into separate entry items

– name into first name and last name

– address into street, city etc

– drop down list/combo box for

– date of birth

– sex

– subjects

– grades

– calendar object for

– date of birth

– radio buttons for

– sex

– hyperlinks for

– NEXT

– BACK [4]

(b) (i) any one point from:

– check on input for errors by double entry

– on screen checking

– check input is same as source

(ii) – name

– address [3]

 

Q 11 (a) E, H [2]

(b) (Engine (litres) > 1.8) OR (CO2 (g/km) > 150)

← (1 mark) → ← (1 mark) →

Or

(CO2 (g/km) > 150) OR (Engine (litres) > 1.8)

← (1 mark) → ← (1 mark) → [2]

(c) G, C, D, B, F, A, E, H

(1 mark for correct order (fuel used)

1 mark for ascending order) [2]

 

Inqilab Ruknuddin Patel

Read More