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A Level Computer Science 9618 Paper 13, May/June 2024

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9618/13 · May/June 2024

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1
a

Complete the following description. A kibibyte has a ................................................ prefix. Three kibibytes is the same as ................................................ bytes. A megabyte has a ................................................ prefix. Two terabytes is the same as ................................................ gigabytes.

[4]
b

Convert the denary number 241 to hexadecimal.

[1]
c

State what is meant by an overflow in binary addition.

[1]
d(i)

Computers use character sets when representing characters in binary. Complete the table by identifying the number of bits each of the character sets allocates to each character. Character set | Number of bits ASCII | extended ASCII | Unicode |

[1]
d(ii)

Explain how the word ‘Clock’ is represented by a character set.

[2]
2

A photograph is stored as a bitmap image.

a

The photograph has a resolution of 4000 pixels wide by 3000 pixels high. The bit depth is 4 bytes. Calculate an estimate for the file size of the photograph in megabytes. Show your working. Working ..................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Answer ...................................... megabytes

[2]
b(i)

The photograph is compressed before being uploaded to a web server. Give three benefits of this photograph being compressed using lossy compression instead of lossless compression. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... 3 ........................................................................................................................................ ...........................................................................................................................................

[3]
b(ii)

Explain how run-length encoding (RLE) will compress the photograph.

[2]
c

Identify two elements of a bitmap image that can be changed to reduce its file size. 1 ................................................................................................................................................ ................................................................................................................................................... 2 ................................................................................................................................................ ...................................................................................................................................................

[2]
3

The following table shows part of the instruction set for a processor. The processor has two registers: the Accumulator (ACC) and an Index Register (IX). Instruction Opcode | Operand | Explanation LDM | #n | Immediate addressing. Load the number n to ACC LDD | <address> | Direct addressing. Load the contents of the location at the given address to ACC LDI | <address> | Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC LDX | <address> | Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC LDR | #n | Immediate addressing. Load the number n to IX ADD | #n/Bn/&n | Add the number n to the ACC ADD | <address> | Add the contents of the given address to the ACC DEC | <register> | Subtract 1 from the contents of the register (ACC or IX) SUB | #n/Bn/&n | Subtract the number n from the ACC SUB | <address> | Subtract the contents of the given address from the ACC INC | <register> | Add 1 to the contents of the register (ACC or IX) <address> can be an absolute or a symbolic address # denotes a denary number, e.g. #123 B denotes a binary number, e.g. B01001010 & denotes a hexadecimal number, e.g. &4A

a

The current contents of memory are shown: Address | Data 48 | 51 49 | 6 50 | 48 51 | 50 52 | 49 53 | 50 54 | 6 The current contents of the ACC and IX are shown: ACC: 2 IX: 50 Complete the table by writing the content of the ACC after each program has run. Program number | Code | ACC content 1 | LDM #50 INC ACC SUB #1 | 2 | LDI 51 ADD 52 | 3 | LDR #2 LDX 50 DEC ACC | 4 | LDD 52 SUB 54 INC ACC |

[4]
b

The processor includes these bit manipulation instructions: Instruction Opcode | Operand | Explanation AND | #n/Bn/&n | Bitwise AND operation of the contents of ACC with the operand AND | <address> | Bitwise AND operation of the contents of ACC with the contents of <address> XOR | #n/Bn/&n | Bitwise XOR operation of the contents of ACC with the operand XOR | <address> | Bitwise XOR operation of the contents of ACC with the contents of <address> OR | #n/Bn/&n | Bitwise OR operation of the contents of ACC with the operand OR | <address> | Bitwise OR operation of the contents of ACC with the contents of <address> LSL | #n | Bits in ACC are shifted logically n places to the left. Zeros are introduced on the right-hand end LSR | #n | Bits in ACC are shifted logically n places to the right. Zeros are introduced on the left-hand end <address> can be an absolute or a symbolic address # denotes a denary number, e.g. #123 B denotes a binary number, e.g. B01001010 & denotes a hexadecimal number, e.g. &4A The current contents of memory are shown: Address | Data 100 | 00001101 101 | 10111110 102 | 11110011 103 | 00110111 104 | 00000000 The current content of the ACC is shown: 1 1 1 1 1 1 1 1 Complete the table by writing the content of the ACC after each instruction has run. The binary number 11111111 is reloaded into the ACC before each instruction is run. Instruction number | Instruction | ACC content 1 | LSL #2 | 2 | XOR 100 | 3 | AND 103 |

[3]
4

A theatre wants to use a database to store data about the shows that are scheduled, their customers and the seats that the customers have booked. In the theatre: • Each show can take place on multiple dates. • Some dates can have more than one performance. • There are multiple rows of seats. • Each seat can be individually booked by its row letter and seat number, for example row E seat 2. Part of the database design includes these tables: SHOW(ShowID, Title, Duration) SEAT(SeatID, RowLetter, SeatNumber) PERFORMANCE(PerformanceID, ShowID, ShowDate, StartTime)

a

Identify the relationship between the tables PERFORMANCE and SHOW.

[1]
b

Sample data for the table PERFORMANCE is shown: PerformanceID | ShowID | ShowDate | StartTime 0001 | MK12 | 5/5/2025 | 13:00 0002 | MK12 | 5/5/2025 | 19:30 0003 | MK12 | 6/5/2025 | 19:00 0004 | OP3 | 7/5/2025 | 18:30 0005 | OP3 | 8/5/2025 | 18:30 0006 | OP3 | 9/5/2025 | 13:00 Write a Structured Query Language (SQL) script to define the table PERFORMANCE.

[4]
c

Write an SQL script to return the number of times each show is scheduled. For example, in the sample data in part (b), the show MK12 is scheduled three times. The result needs to include the show name and a suitable field name for the number of times it is scheduled.

[4]
d

Customers give their first name, last name and email address when they are making a booking. One booking can include multiple seats. Describe the additional tables that will need to be included in the database and explain how these tables will be linked within the database.

[5]
5

A multimedia design company has an office with a LAN (local area network). The LAN can have up to 20 devices connected with cables and other devices connected using wireless access.

a(i)

The company has private cloud storage for its employees to store their work. Define the term private cloud.

[1]
a(ii)

Describe the benefits to the company of using private cloud storage instead of public cloud storage.

[3]
b

Part of the internal structure of the wired LAN is a star topology. Explain how packets are transmitted between two devices in a star topology.

[2]
c(i)

A different part of the network uses the Ethernet protocol. A collision is detected. Describe how the collision is managed using Carrier Sense Multiple Access/Collision Detection (CSMA/CD).

[2]
c(ii)

Identify two drawbacks of using CSMA/CD. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ...........................................................................................................................................

[2]
d

The devices in the office have static private IP addresses. State what is meant by a static private IP address.

[1]
6

Each of the following truth tables has three inputs (A, B and C) and one output (X). Draw one line to match each truth table with its logic expression. Truth table Logic expression A B C X 0 0 0 0 0 0 1 1 0 1 0 0 0 1 1 0 1 0 0 1 1 0 1 1 1 1 0 0 1 1 1 0 NOT (A XOR B) AND C A B C X 0 0 0 0 0 0 1 1 0 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 0 1 1 1 1 (A OR C) AND NOT B A NAND B NAND C A B C X 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 0 1 1 1 1 (A NAND B) OR C NOT (A AND B AND C)

[3]
7

Robots are used to serve food and drink to customers at a restaurant.

Figure 1 of 1 for question 7
a

A robot navigates through the restaurant to the table it is serving. Complete the table by identifying two sensors that can be included in the robot and the purpose of each sensor in the navigation system. Sensor | Purpose of sensor in navigation system .............................................. | .......................................................................................... .............................................. | .......................................................................................... .............................................. | .......................................................................................... .............................................. | ..........................................................................................

[2]
b

The robot uses Artificial Intelligence (AI) to communicate with the customers. The customers speak to the robot to order their food and drinks. Explain how AI will be used in this part of the robot.

[3]
c

The navigation system can be considered an example of a control system. Describe how feedback is used in a control system.

[2]
d

The robot includes a touchscreen for the customer to make their payment. Describe the principal operation of a touchscreen.

[4]
e(i)

Program libraries were used when writing the robot’s software. State what is meant by a program library.

[1]
e(ii)

Some program libraries include Dynamic Link Library (DLL) files. Describe the benefits of a programmer using a library with DLL files instead of using a library that does not include DLL files.

[4]
f(i)

The data from the robots is transmitted to a central computer using a wireless connection. Complete the table by identifying and describing two methods of data verification that can be used during data transfer. Method | Description 1 ......................................... | .......................................................................................... ......................................... | .......................................................................................... | .......................................................................................... | .......................................................................................... 2 ......................................... | .......................................................................................... ......................................... | .......................................................................................... | .......................................................................................... | ..........................................................................................

[4]
f(ii)

Explain how encryption can protect the security of data during transmission.

[2]

Mark scheme

9618/13 · May/June 2024

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1a · 4 marks

  • 1 mark

    binary

  • 1 mark

    3072

  • 1 mark

    denary/decimal

  • 1 mark

    2000

1b · 1 mark

  • 1 mark

    F1

1c · 1 mark

  • 1 mark

    The answer is too long to be represented in the same number of bits as the binary numbers being added

1d(i) · 1 mark

  • 1 mark

    ASCII: 7, extended ASCII: 8, Unicode: 16/32 (all 3 correct)

1d(ii) · 2 marks

  • 1 mark

    Each character has a unique binary code

  • 1 mark

    The binary code for each character is stored in sequence

2a · 2 marks

  • 1 mark

    4000 * 3000 * 4

  • 1 mark

    48MB

2b(i) · 3 marks

  • 1 mark

    The file takes less storage space on the web server than if lossless compression was used

  • 1 mark

    The file is faster to upload/download to/from the server than if lossless compression was used

  • 1 mark

    The file uses less bandwidth to transmit than if lossless compression was used / The file consumes less data allowance than if lossless compression was used

2b(ii) · 2 marks

  • 1 mark

    Identifies consecutive repeating pixels of the same colour

  • 1 mark

    Stores the colour /pattern and the number of times it repeats

2c · 2 marks

  • 1 mark

    Colour/bit depth

  • 1 mark

    Image resolution

3a · 4 marks

  • 1 mark

    Program 1: 50

  • 1 mark

    Program 2: 97

  • 1 mark

    Program 3: 48

  • 1 mark

    Program 4: 44

3b · 3 marks

  • 1 mark

    Instruction 1 (LSL #2): 1111 1100

  • 1 mark

    Instruction 2 (XOR 100): 1111 0010

  • 1 mark

    Instruction 3 (AND 103): 0011 0111

4a · 1 mark

  • 1 mark

    many to 1 // there are many performances of each show

4b · 4 marks

  • 1 mark

    Creating table PERFORMANCE with opening and closing brackets

  • 1 mark

    Setting all four attributes with appropriate data types

  • 1 mark

    Setting PerformanceID as primary key

  • 1 mark

    Setting ShowID as foreign key referencing SHOW table

4c · 4 marks

  • 1 mark

    Selecting COUNT of an attribute in PERFORMANCE table with suitable name

  • 1 mark

    FROM clause

  • 1 mark

    Joining tables

  • 1 mark

    Grouping by the title and selecting the title

4d · 5 marks

  • 1 mark

    CUSTOMER table identified with suitable Primary Key and appropriate name

  • 1 mark

    … and other suitable fields including name and email

  • 1 mark

    BOOKING TABLE identified with suitable Primary Key and appropriate name

  • 1 mark

    … that stores the Primary Key of the CUSTOMER table as a Foreign Key to join with CUSTOMER table / … and stores the Primary Key of the PERFORMANCE table as a Foreign Key to join with PERFORMANCE table

  • 1 mark

    A linking table between Table 2 and SEAT with suitable Primary Key and appropriate name (including foreign keys / SeatID)

5a(i) · 1 mark

  • 1 mark

    Dedicated/bespoke services/storage on a remote server only available to company

5a(ii) · 3 marks

  • 1 mark

    Not reliant on a third party

  • 1 mark

    … gives greater control over security/privacy / … gives greater control over backup

  • 1 mark

    Storage can be tailored/scalable to company requirements // an example e.g. the amount of storage accessible/ facilitating the sharing of files

5b · 2 marks

  • 1 mark

    Sending computer transmits packets directly to switch/router/central device

  • 1 mark

    Switch/router/central device checks destination address of packet and forwards directly to that device

5c(i) · 2 marks

  • 1 mark

    Jamming signal is transmitted by the sending device / Transmission is aborted

  • 1 mark

    The sending device waits a random time before trying to send data again ... / ... if further collisions occur the wait time is increased

5c(ii) · 2 marks

  • 1 mark

    Random time increased each time so can be infinite waiting / May be constant jamming signal so nothing ever sends / Certain nodes cannot be prioritised

  • 1 mark

    High power consumption / Only suitable for short distance network // limited distance / Not scalable // more nodes means exponentially longer waiting times

5d · 1 mark

  • 1 mark

    Static means the IP for that device does not change and Private means it can only be accessed/seen/used within the LAN

6 · 3 marks

  • 1 mark

    Truth table 1 joined to (A OR C) AND NOT B

  • 1 mark

    Truth table 2 joined to NOT (A XOR B) AND C

  • 1 mark

    Truth table 3 joined to (A NAND B) OR C

7a · 2 marks

  • 1 mark

    Pressure: To detect if a table or other obstacle has been hit // to detect when food is put on/taken off the tray so it can move on

  • 1 mark

    Infra-red: To detect if there is an obstacle in the way // to indicate that it has reached the desired table (or Sound: To detect if someone is speaking so that it can use AI to decipher the speech and whether the robot is required to stop)

7b · 3 marks

  • 1 mark

    Voice/speech recognition is used / ... to identify if someone speaking / The sound is recorded and analysed

  • 1 mark

    The audio recordings are compared to a database of words/sound waves / ... to identify the word that has the highest probability of being said

  • 1 mark

    Natural language recognition is used / Words are combined and compared to known sentences / … programmed action(s) for matching sentence(s) are performed

7c · 2 marks

  • 1 mark

    Feedback ensures that a system operates within set criteria / constraints

  • 1 mark

    ... by enabling system output to affect subsequent system input / ... thus allowing conditions to be automatically adjusted

7d · 4 marks

  • 1 mark

    Resistive: The space between the conductive layers is removed/the layers touch and a circuit is completed

  • 1 mark

    Capacitive: The electrical charge changes where the user pressed

  • 1 mark

    The point of contact is identified / ... from the change in electrical field

  • 1 mark

    The software/microprocessor calculates the coordinates

7e(i) · 1 mark

  • 1 mark

    Pre-written code/functions/routines that can be imported/called in another program

7e(ii) · 4 marks

  • 1 mark

    Maintenance not needed to be done by the programmer

  • 1 mark

    ... because the DLL is separate from program

  • 1 mark

    The calling program does not need recompilation by the programmer when a DLL file changes / ... because the DLL file can be updated independently of the calling program

  • 1 mark

    … updates will apply to all programs that use the DLL file

7f(i) · 4 marks

  • 1 mark

    Method 1 correctly named (Parity byte / Parity block / Checksum)

  • 1 mark

    Description matching Method 1

  • 1 mark

    Method 2 correctly named

  • 1 mark

    Description matching Method 2

7f(ii) · 2 marks

  • 1 mark

    Encodes/scrambles data / ... so if it is intercepted it cannot be understood

  • 1 mark

    Algorithm/key is required to decode the data

Questions

  1. 1
    Question 19 marks
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  2. 2
    Question 29 marks
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  3. 3
    Question 37 marks
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  4. 4
    Question 414 marks
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  5. 5
    Question 511 marks
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  6. 6
    Question 63 marks
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  7. 7
    Question 722 marks
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