CP5 Computing June 2002

1(i)

Explain the term batch processing.

[1]

similar jobs are queued together and run as a 'batch', usually at off-peak times eg overnight.

(ii)

Describe an application which would use batch processing, making it clear why batch processing is appropriate in this case.

[2]

a monthly payroll application for a company to produce payslips etc
there is no need for 'instant' processing and data for all the staff can be run together as a batch.

2(a)

A multi-user computer system uses passwords to try to maintain security.
Describe two guidelines which should be adopted in the use of passwords.

[2]

do not use 'obvious' passwords eg names, dates of birth, pet names etc
change the password regularly.

(b)

Explain what is meant by the term data encryption and explain how encrypted data can be read by the appropriate person.

[2]

'coding' the data so it is unreadable.
the data can only be de-crypted by the appropriate person who has a 'key'.

(c)

It is sensible for organisations to carry out disaster planning for their computer systems.

(i) Why is this particularly important?

[1]

so that important data can be recovered after a disaster has occurred, and the organisation can carry on its business.

(ii) Describe two elements of disaster planning which can allow an organisation to recover quickly following a disaster to a computer system.

[2]

damaged hardware needs to be replaced and software needs to be re-installed.
data needs to be re-loaded from backups

A company produces computer games. It advertises these on its web site, which contains a large number of pages. Describe two ways in which a user of the web site might find the information he or she needs.

[2]

follow links to other pages until the information is found.
use an on-site search engine to find the correct web page.

4(a)

(i) Explain the term indexed sequential file

[2]

each record of the file has a key field and the file is sorted in order of this key field.
an index of keys can be used to find records.

(ii) Explain the term multi-level index.

[2]

looking up a record key in one index returns another index...where looking for the key returns another index...
...and so on until the address of the record is returned.

(b)

The Xtrafine company stores information in fixed length records in an indexed sequential file with a multi-level index to store details of its customer accounts.

(i) Explain an advantage of this arrangement over a standard sequential file.

[1]

it allows much faster direct access to single records.

(ii) Explain an advantage of this arrangement over a random access file.

[1]

it allows sequential access of the records if all of them need to be processed.

(iii) Explain why an overflow area will be necessary with an indexed sequential file and why this will result in the need for file re-organisation.

[3]

when new records are added, there may not be enough space to store them in the position indicated by the index.
a pointer would be left indicating the position of the overflow area where the added record is stored.
eventually the overflow area would be filled and the records in it would need to be merged with the main fiel and re-indexed, so a new empty overflow area can be started.

(c)

The Zanadu company stores details of its customers in a random access file using a hashing algorithm.

(i) State the advantage of a random access file over a sequential file.

[1]

it is much faster to access a single record.

(ii) I. Outline the function of a hashing algorithm.

[1]

the hashing algorithm performs a calculation which returns the address of where a record is stored.

II. What data element is used as an input to the hashing algorithm?

[1]

the key field of the record required.

III. A simple hashing algorithm used by Zanadu is one which converts a six digit input number as follows:

The six digits are added together, then the result is divided by 29, and the remainder is used as the output from the algorithm.

Calculate the output, if the input is 931796

[1]

9+3+1+7+9+6 = 35, divided by 29 gives a remainder of ...
6

5(a)

Data are transmitted through a wide area network, using full duplex and packet switching.

(i) Explain what is meant by the term full duplex.

[1]

data can be transmitted both ways simultaneously.

(ii) Explain in detail the term packet switching, making clear the advantage of packet switching over circuit switching.

[3]

data messages are split into equal-sized 'packages' which include the address of the destination
these packages are transmitted down the network and are routed to their destination
when all the packages have arrived they are reassembled at the destination into the original message.

(b)

Describe what is meant by the term data collision on a network and describe how the network deals with data collisions.

[2]

when two packets of data are transmitted at the same time and corrupt each other.
before transmission a computer will check to see if the data channel is free and will wait if it is not.

(c)

What is meant by the term gateway in a computer network?

[1]

a gateway is a computer connecting two networks which may use different protocols and will convert data to the proper format if necessary.

(d)

Explain why protocols are required in networks.

[1]

protocols are standard rules for transmitting data and are needed so that different computers can interpret each others messages.

(e)

(i) What is meant by the term distributed system?

[2]

a system that uses a number of different computers to operate.
but the user thinks he is using a single computer.

(ii) Give an example of a distributed system.

[1]

a country-wide airline traffic control system

6(i)

Explain what is meant by the term primary key in a database.

[1]

a field which uniquely identifies a record.

(ii)

Using an example, explain why a primary key might need to be a combination of more than one field.

[2]

if none of the individual fields uniquely identifies a record then the primary key would need to be a combination of two or more fields.
eg ENTRIES (PupilNumber, ExamNumber, Date)

PupilNumber	ExamNumber	Date
234	1056	12/6/02
234	1085	13/6/02
256	1085	13/6/02
...	...	...

The primary key would need to be a combination of the PupilNumber and the ExamNumber.

7(a)

(i) Explain the meaning of the computer term interrupt.

[1]

a signal sent to the CPU from a hardware device.

(ii) Give two examples of situations where interrupts may occur.

[2]

a printer may send an interrupt when it is ready to receive more data.
a run-time error in a program may send an interrupt to the CPU

(b)

Using an example, explain the meaning of the term double buffering.

[2]

Eg when data is being sent to a printer, two buffers are used. These are areas of memory which are filled with data to be printed.
One buffer can be filled while the other is being emptied to the printer. This will speed up the printing process.

An outdoor equipment shop orders supplies from a number of suppliers.

The table below shows a sample of orders made during one particular week. The orders are stored ina database.

Order Number	Quantity Ordered	Item Code	Item Name	Manufacturer Code	Manufacturer Name	Manufacturer Contact
2349	7	2467	Fleece	M451	Warmpile	Ms Miah
2566	12	6722	Trousers	M740	Highline	Mr Ovien
2677	1	4333	Boots	M451	Warmpile	Ms Miah
2971	8	1255	Fleece	M809	Carnedd	Mr Heath
3002	1	2467	Fleece	M451	Warmpile	Ms Miah
3007	6	4333	Boots	M451	Warmpile	Ms Miah
3010	20	1220	Gloves	M809	Carnedd	Mr Heath
3198	2	6722	Trousers	M740	Highline	Mr Ovien
.......	......	.....	.....	.....	.....	.....

(i)

These data are not normalised.
Describe two problems associated with data not being normalised, giving a specific example in each case from the above data.

[4]

data redundancy - data is duplicated causing unnecessary waste of storage space.
Example - the manufacturer's name 'Warmpile' is repeatedly stored in the above data.
data inconsistency - if data is stored more than once there may be differences (eg in spelling)
Example the manufacturer's contact 'Mr Heath' may have been mis-spelled in one field as 'Mr Heeth'. The computer will not know which one is correct.

(ii)

Explain what is meant by the term third normal form.

[2]

In any table, all the fields which are not keys (or partial keys) are dependent only on the key field.
A table may have foreign fields which are key fields for other tables (ie linking the two tables)

(iii)

Restructure this database into third normal form. There is no need to copy the items of data.

[9]

ORDERS(OrderNumber, QuantityOrdered, ItemCode)
ITEMS(ItemCode, ItemName, ManufacturerCode)
MANUFACTURERS(ManufacturerCode, ManufacturerName, ManufacturerContact)

In the following question, additional credit ( up to 3 marks) will be gained if your answer demonstrates skill in written communication.

Many industrial plants use computer controlled equipment, including robotic machinery in the manufacturing process. The introduction of this equipment has affected manufacturing performance, the safety of the workforce and employment.

Describe the advantages and disadvantages of using computer controlled equipment compared with human workers.

[8 + 3]

Robotic machinery has been installed in many cases to perform tasks which are either monotonous or dangerous. Eg Handling radioactive material or operating in hostile environments. This has taken human workers out of dangerous situations.

Robots do not need breaks or holidays and can operate for 24 hours a day, thus improving manufacturing output, and after the initial cost they are reasonably inexpensive to run. Unlike humans they do not require a monthly pay cheque.

Robots also do not tire and so perform optimally all the time, minimising the risk of errors being made. They will also work at optimal speed constantly.

One disadvantage of robotic machinery is that it is unable to analyse a situation where things have gone wrong and take appropriate action as a human would be able to do.

The effect on employment is arguable. It is true that robots have replaced humans in a number of jobs but it has also meant that new jobs have been created. Eg robot maintenance, robot programmers etc..