AS LEVEL 9608 Computer Science - Students Resource

AS LEVEL 9608

Computer Science Paper 1

TOPICAL WORKBOOK

WITH MARK SCHEME

JUNE 2015 – NOVEMBER 2019

Reviewed By:

FAWAD KHAN

Topic: Introduction ___________________________________________________________________________________________________Computer Science Paper 1 Topical

By: ALI AKRAM Airport Road | Bahria Town | Johar Town3

Computer Science Topical Paper 1 Content

Introduction Preface………………………………………………………………………………………..… 4 About the author…………………………………………………………………………….5 Acknowledgment ……………………………………………………………………………6

Topic 1 Information Representation ………………………………………………………….. 7 Mark Scheme…………………………………………………………………………….… 44

Topic 2 Communication and Internet Technologies……………………………….…. 65 Mark Scheme……………………………………………………………………………….. 97

Topic 3 Hardware…………………………………………………………………………………… 116 Mark Scheme…………………………………………………………………………….. 159

Topic 4 Processor Fundamentals……………………………………………………………. 194 Mark Scheme…………………………………………………………………………….. 260

Topic 5 System Software……………………………………………………………………….. 290 Mark Scheme…………………………………………………………………………….. 309

Topic 6 Security, Privacy and Data Integrity……………………………………………. 325 Mark Scheme…………………………………………………………………………….. 343

Topic 7 Ethics and Ownership………………………………………………………………….356 Mark Scheme…………………………………………………………………………….. 370

Topic 8 Database and Data modeling……………………………………………………… 379 Mark Scheme…………………………………………………………………………….. 416

Convert the following binary number into hexadecimal.

1 0 1 1 1 0 0 0

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

(ii) Convert the following denary number into BCD format.

9 7

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

(iii) Using two’s complement, show how the following denary numbers could be stored in an 8-bit register:

114

- 93

[2]

9608/11/M/J/15/Q1

Sound can be represented in a computer in a digital format.

(i) Give the definition of the term sampling.

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

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

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

(ii) Give one reason why 16-bit sampling is used in an audio compact disc (CD).

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9608/11/M/J/15/Q2

(iii) Explain what is meant by the term sampling resolution.

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.......................................................................................................................................[2]

(i)

(a)

1

2

Topic 1: Information Representation___________________________________________________________________________________________________Computer Science Paper 1 Topical

By: ALI AKRAM Airport Road | Bahria Town | Johar Town

Topic 1 Information Representation

___________________________________________________________________________________________________7

(iv) Give one benefit and one drawback of using a higher sampling resolution.

Benefit ...............................................................................................................................

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

Drawback ..........................................................................................................................

.......................................................................................................................................[2]

(b) Describe two typical features found in software for editing sound files.

1 ................................................................................................................................................

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

2 ................................................................................................................................................

...............................................................................................................................................[2]

(c) Explain the difference between lossless and lossy data compression techniques.

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

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By: ALI AKRAM Airport Road | Bahria Town | Johar Town___________________________________________________________________________________________________

8

(i) Using two’s complement, show how the following denary numbers could be stored in an 8-bit register:

124

–77

[2]

(ii) Convert the two numbers in part (a) (i) into hexadecimal.

124 ..................................................................................................................................

–77 ................................................................................................................................... [2]

(b) Binary Coded Decimal (BCD) is another way of representing numbers.

(i) Write the number 359 in BCD form.

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

(ii) Describe a use of BCD number representation.

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

...................................................................................................................................... [2]

9608/13/M/J/15/Q1 (a)

3



9

1 (i) B 8 [1] (ii) 1 0 0 1 0 1 1 1 [1] (iii)

114

0

1 1 1 0 0 1 0

– 93

1

0 1 0 0 0 1 1

[2]

(i) Any one from:

• amplitude of sound wave taken at different points in time

• measurement of value of analogue signal at regular time intervals/a point in time [1] (ii) Any one from:

• bit depth/sampling resolution sufficient for good quality sound

• higher bit depth/sampling resolution would mean bigger files

• ...hence less (music) content on each CD

• can represent dynamic range of about 90 dB

• 90 dB is basically the maximum dynamic range of human hearing

• compromise between quality and reasonable file size [1] (iii) Any two from:

• resolution is the number of distinct values available to encode/represent each sample

• specified by the number of bits used to store/record each sample

• sometimes referred to as bit depth

• the higher the sampling resolution, the smaller the quantization error

• a higher sampling resolution results in less distortion of the sound

• usually 8 bit, 16 bit, 24 bit or 32 bit [2] (iv) 1 mark for benefit and 1 mark for drawback.

benefit

• allows for larger dynamic ranges

• ...as dynamic range is approximately six times the bit depth

• more accurate representation/crisper sound quality

drawback

• bigger files/occupies more memory/storage

• longer to transmit data/download music

• greater processing power needed [2]

(a) 2

Topic 1: Mark Scheme___________________________________________________________________________________________________Computer Science Paper 1 Topical


44

Telephone calls can be made by using: • conventional telephones (using the Public Service Telephone Network (PSTN) system)

over a wired network • a computer, equipped with speakers and microphone, connected to the Internet

Put a tick () in the correct column to match each description to the appropriate communication method.

Description Conventional telephone using PSTN Internet-based system

connection only in use whilst sound is being transmitteddedicated channel used between two points for the duration of the callconnection maintained throughout the telephone callencoding schemes and compression technology usedlines remain active even during a power outage

[5]

(b) Distinguish between the Internet and the World Wide Web (WWW).

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

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...............................................................................................................................................[3]

9608/11/M/J/15/Q5

(c) Name the hardware device that is being described:

(i) A device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by the most efficient route.

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

(ii) A device used between two dissimilar LANs. The device is required to convert data packets from one protocol to another.

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

(iii) A device or software that provides a specific function for computers using a network. The most common examples handle printing, file storage and the delivery of web pages.

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

(a) 1

Topic 2 Communication & Internet Tech.___________________________________________________________________________________________________Computer Science Paper 1 Topical


Topic 2 Communication and Internet Technologies

___________________________________________________________________________________________________65

Explain the term bit streaming.

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

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...............................................................................................................................................[2]

(b) A person watches a film streamed from a website on a tablet computer.

(i) Give two benefits of using bit streaming for this purpose.

1 ........................................................................................................................................

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

2 ........................................................................................................................................

...........................................................................................................................................[2]

(ii) State two potential problems of using bit streaming for this purpose.

1 ........................................................................................................................................

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

2 ........................................................................................................................................

...........................................................................................................................................[2]

(c) Explain the terms on-demand bit streaming and real-time bit streaming.

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9608/11/O/N/15/Q1 (a)

2 Topic 2 Communication & Internet Tech.___________________________________________________________________________________________________Computer Science Paper 1 Topical


66

The table shows four statements about IP addresses.

Tick (✓) to show which of the statements are true.

Statement True (✓)

The IP address consists of any number of digits separated by single dots (.)

Each number in an IP address can range from 0 to 255

IP addresses are used to ensure that messages and data reach their correct destinations

Public IP addresses are considered to be more secure than private IP addresses

[2]

(b) Consider the URL:

http://cie.org.uk/computerscience.html

(i) Give the meaning of the following parts of the URL.

http ....................................................................................................................................

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

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

cie.org.uk ...........................................................................................................................

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

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

computerscience.html .......................................................................................................

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

...........................................................................................................................................[3]

(ii) Sometimes the URL contains the characters %20 and ?.

Describe the function of these characters.

%20 ...................................................................................................................................

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

? ........................................................................................................................................

...........................................................................................................................................[2]

9608/11/O/N/15/Q3 (a)

3 Topic 2 Communication & Internet Tech.___________________________________________________________________________________________________Computer Science Paper 1 Topical


67

Description

Conventional telephone

using PSTN

Internet-based system

connection only in use whilst sound is being transmitted

�

dedicated channel used between two points for the duration of the call

�

connection maintained throughout the telephone call

�

encoding schemes and compression technology used

�

lines remain active even during a power outage �

[5]

(b) maximum of two marks for Internet references and maximum of two marks for world wide

web references Internet

• massive network of networks/interconnected network of computer devices

• Internet stands for Interconnected Networks

• uses TCP/IP protocol

World Wide Web (www)

• is a collection of (multimedia) web pages/documents

• ...stored on websites

• http/protocols used to transmit data

• web pages are written in HTML

• URLs specify the location of the web pages

• web documents are accessed using browsers [3]

(c) (i) router [1]

(ii) gateway [1]

(iii) server [1]

(a) 1



97

Name the most suitable input or output device for each of the following uses.

Give a different device in each case.

Description of use Input or output device

input of credit card number into an online form

selection of an option at an airport information kiosk

output of a single high-quality photograph

output of several hundred high-quality leaflets

input of a hard copy image into a computer

[5]

(b) All of the uses in part (a) involve the input or output of data.

(i) Describe two methods of preventing accidental loss of data.

1 ........................................................................................................................................

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

2 ........................................................................................................................................

.......................................................................................................................................[2]

(ii) Describe one way of ensuring the security of the data against malicious damage.

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

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

9608/11/M/J/15/Q6 (a)

1

Topic 3: Hardware___________________________________________________________________________________________________Computer Science Paper 1 Topical


Topic 3 Hardware

___________________________________________________________________________________________________116

A system is monitored using sensors. The sensors output binary values corresponding to physical conditions, as shown in the table:

Parameter Description of parameter

Binary value Description of condition

P oil pressure1 pressure >= 3 bar

0 pressure < 3 bar

T temperature1 temperature >= 200°C

0 temperature < 200°C

R rotation1 rotation <= 1000 revs per minute (rpm)

0 rotation > 1000 revs per minute (rpm)

The outputs of the sensors form the inputs to a logic circuit. The output from the circuit, X, is 1 if any of the following three conditions occur:

either oil pressure >= 3 bar and temperature >= 200°C

or oil pressure < 3 bar and rotation > 1000 rpm

or temperature >= 200°C and rotation > 1000 rpm

(a) Draw a logic circuit to represent the above system.

P

T X

R

[5]

9608/11/M/J/15/Q7 2 Topic 3: Hardware___________________________________________________________________________________________________Computer Science Paper 1 Topical


117

(b) Complete the truth table for this system.

P T RWorkspace

X

0 0 0

0 0 1

0 1 0

0 1 1

1 0 0

1 0 1

1 1 0

1 1 1

[4]

Topic 3: Hardware___________________________________________________________________________________________________Computer Science Paper 1 Topical


118

There are two types of RAM: dynamic RAM (DRAM) and static RAM (SRAM).

Five statements about DRAM and SRAM are shown below.

Draw a line to link each statement to the appropriate type of RAM.

Statement Type of RAM

requires data to be refreshed periodically in order to retain the data

has more complex circuitryDRAM

does not need to be refreshed as the circuit holds the data as long as the power supply is on

requires higher power consumption which is significant when used in battery-powered devices

SRAM

used predominantly in cache memory of processors where speed is important

[5]

9608/13/M/J/15/Q4

(b) Describe three differences between RAM and ROM.

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(c) DVD-RAM and flash memory are two examples of storage devices.

Describe two differences in how they operate.

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.............................................................................................................................................. [2]

(a) 3 Topic 3: Hardware___________________________________________________________________________________________________Computer Science Paper 1 Topical


119

Description of use

Input or output device

input of credit card number into an online form

Keyboard/keypad/numberpad

selection of an option at an airport information kiosk

touch screen

output of a singe high quality photograph

ink jet printer

output of several hundred high quality leaflets

laser printer

input of a hard copy image into a computer

scanner

[5]

(b) (i) Any two from:

• frequent (or equivalent) backup EITHER to secondary media/to 3rd party server/cloud/removable devices/continuous backup OR stored remotely

• disk-mirroring strategy/RAID

• UPS (uninterruptable power supply)/backup generator [2]

(ii) Any one from:

• protection of data (or equivalent) with passwords/using password and username for logging on include e.g. fingerprint scanning

• encryption

• installation and use of up to date anti-malware/anti-virus

• give different access rights to different users

• use a firewall,

• physical methods/lock doors and use secure entry devices/CCTV [1]

(a) 1



159

Five modes of addressing and five descriptions are shown below.

Draw a line to connect each mode of addressing to its correct description.

Mode of addressing Description

directthe operand is the address of the address of the value to be used

immediatethe operand is the address of the value to be used

indexedthe operand is the offset from the current address where the value to be used is stored

indirectthe operand plus the contents of the index register is the address of the value to be used

relative the operand is the value to be used

[4]

9608/11/M/J/15/Q3

Explain how the width of the data bus and system clock speed affect the performance of a computer system.

Width of the data bus ................................................................................................................

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Clock speed ..............................................................................................................................

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...............................................................................................................................................[3]

9608/11/M/J/15/Q8 (a)

1

2

Topic 4: Processor Fundamentals___________________________________________________________________________________________________Computer Science Paper 1 Topical


Topic 4 Processor Fundamentals

___________________________________________________________________________________________________194

(b) Most computers use Universal Serial Bus (USB) ports to allow the attachment of devices.

Describe two benefits of using USB ports.

1 ................................................................................................................................................

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

2 ................................................................................................................................................

...............................................................................................................................................[2]

(c) The table shows six stages in the von Neumann fetch-execute cycle.

Put the stages into the correct sequence by writing the numbers 1 to 6 in the right hand column.

Description of stage Sequence number

the instruction is copied from the Memory Data Register (MDR) and placed in the Current Instruction Register (CIR)

the instruction is executed

the instruction is decoded

the address contained in the Program Counter (PC) is copied to the Memory Address Register (MAR)

the value in the Program Counter (PC) is incremented so that it points to the next instruction to be fetched

the instruction is copied from the memory location contained in the Memory Address Register (MAR) and is placed in the Memory Data Register (MDR)

[6]

Assemblers translate from assembly language to machine code. Some assemblers scan the assembly language program twice; these are referred to as two-pass assemblers.

The following table shows five activities performed by two-pass assemblers.

Write 1 or 2 to indicate whether the activity is carried out during the first pass or during the second pass.

Activity First pass or second pass

any symbolic address is replaced by an absolute address

any directives are acted upon

any symbolic address is added to the symbolic address table

data items are converted into their binary equivalent

forward references are resolved

[5]

9608/13/M/J/15/Q2 3



195

Name and describe three buses used in the von Neumann model.

Bus 1 .........................................................................................................................................

Description ................................................................................................................................

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

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

Bus 2 .........................................................................................................................................

Description ................................................................................................................................

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

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

Bus 3 .........................................................................................................................................

Description ................................................................................................................................

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

................................................................................................................................................... [6]

(b) The sequence of operations shows, in register transfer notation, the fetch stage of the fetch-execute cycle.

1 MAR ← [PC] 2 PC ← [PC] + 1 3 MDR ← [[MAR]] 4 CIR ← [MDR]

• [register] denotes contents of the specified register or memory location • step 1 above is read as “the contents of the Program Counter are copied to the Memory

Address Register”

(i) Describe what is happening at step 2.

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

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

(ii) Describe what is happening at step 3.

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

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

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

9608/13/M/J/15/Q5 (a) 4



196

[4]

the operand is the address of the address of the value to be used

the operand is the address of the value to be used

the operand is the offset from the current address where the value to be used is stored

the operand plus contents of index register is the address of the value to be used

the operand is the value to be used

direct

immediate

indexed

indirect

relative

1



260

A game program is written which can be either interpreted or compiled. The table below shows five statements about the use of interpreters and compilers.

Tick (✓) to show whether the statement refers to an interpreter or to a compiler.

Statement Interpreter Compiler

This translator creates an executable file

When this translator encounters a syntax error, game execution halts

The translator analyses and checks each line just before executing it

This translator will produce faster execution of the game program

Use of this translator makes it more difficult for the user to modify the code of the game

[5]

9608/11/O/N/15/Q11

Three examples of language translators and four definitions are shown below. Draw lines to link each language translator to the correct one or more definitions.

DefinitionLanguage translator

The software reads the source code and reports all errors. The software produces an executable file.

The software reads each statement and checks it before running it. The software halts when it encounters a syntax error.

The software translates a high-level language program into machine code for the processor to execute.

The software translates low-level statements into machine code for the processor to execute.

Compiler

Assembler

Interpreter

[3]

9608/11/M/J/16/Q1

1

2

Topic 5: System Software___________________________________________________________________________________________________Computer Science Paper 1 Topical


Topic 5 System Software

___________________________________________________________________________________________________290

Describe two differences between a compiler and interpreter.

1 .......................................................................................................................................................

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2 .......................................................................................................................................................

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9608/13/M/J/16/Q1 3 Topic 5: System Software___________________________________________________________________________________________________Computer Science Paper 1 Topical


291

A small company produces scientific magazines. The owner buys some new desktop computers. The computers are used to store thousands of colour images (diagrams and photographs). All the computers have Internet access.

(a) Name three utility programs the company would use on all their computers. Describe what each program does.

1 ................................................................................................................................................

Description ................................................................................................................................

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

2 ................................................................................................................................................

Description ................................................................................................................................

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

3 ................................................................................................................................................

Description ................................................................................................................................

...............................................................................................................................................[6]

(b) The images contained in the magazines are produced using either bitmap or vector graphics software.

Give four differences between bitmap and vector graphics.

1 ................................................................................................................................................

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2 ................................................................................................................................................

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3 ................................................................................................................................................

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4 ................................................................................................................................................

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9608/11/O/N/16/Q7 4 Topic 5: System Software___________________________________________________________________________________________________Computer Science Paper 1 Topical


292

Statement Interpreter Compiler

This translator creates an executable file �

When this translator encounters a syntax error, game execution will halt

�

The translator analyses and checks each line just before executing it

�

This translator will produce faster execution of the game program

�

Use of this translator makes it more difficult for the user to modify the code of the game supplied to the user

�

1 mark for each correct row [5]

mark for each box on the left. [3] Term Definition

Marks allocated as follows:

Compiler – 1 mark for two correct connecting lines Assembler – 1 mark for one correct connecting line Interpreter – 1 mark for two correct connecting lines


Assembler

Interpreter



The software translates a high level language program into machine code for the processor to execute

Compiler

Marks allocated as follows:

Compiler – for correct connecting lines Assembler – for correct connecting line Interpreter – for correct connecting lines


Assembler

Interpreter



The software translates a high level language program into machine code for the processor to execute

Compiler

1

One

2



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AS LEVEL 9608 Computer Science - Students Resource