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A Level Computer Science 9618 Paper 11, May/June 2025

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9618/11 · May/June 2025

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1
Figure 1 of 2 for question 1
Figure 2 of 2 for question 1
a

Write the logic expressions for the following logic circuit. X = ............................................................................................................................................ Y = ............................................................................................................................................

[2]
b

Complete the truth table for the following logic circuit.

[2]
2

Programmers in a software development company take part in live video conferences to discuss their work. The live video conferences take place using real-time bit streaming. The video is compressed before it is transmitted.

a

Explain how data is transferred using real-time bit streaming.

[4]
b(i)

Explain the reasons why a video is compressed before it is transmitted using real-time bit streaming.

[4]
b(ii)

Identify whether the lossy or lossless compression method is more appropriate for real-time bit streaming. Justify your answer. Compression method ........................................................................................................ Justification .......................................................................................................................

[3]
c

The video conference is accessed over the internet. Complete the table by stating how modems and dedicated lines are used when data is transmitted over the internet.

[2]
3

A computer stores images and text files.

a

One of the images is a bitmapped image. Complete the table by writing the answer for each statement.

[3]
b(i)

The text in the files is stored using the Unicode character set. Give two advantages of using the Unicode character set instead of using the ASCII character set. 1 ........................................................................................................................................ 2 ........................................................................................................................................

[2]
b(ii)

The Unicode character '❮' has the binary value: 0010 0111 0110 1110 Convert the binary value for the character '❮' into denary.

[1]
b(iii)

The Unicode character '⅀' has the hexadecimal value 2140 Convert the hexadecimal code for the character '⅀' into denary.

[1]
4

A shop installs a new system that allows users to purchase items without going through a manual checkout. The new system: • identifies customers when they enter the shop and matches them to their account • prevents a customer from walking through the automatic barriers if they do not have an account • automatically detects the items that a customer has taken from a shelf and charges these to the customer’s account.

a

The new system uses digital cameras and Artificial Intelligence (AI) to identify the customers. Explain how the new system uses AI to identify each customer.

[4]
b

The new system uses sensors to identify the items taken from a shelf. Identify one type of sensor that can be used in this new system. State how the sensor can be used to identify the items taken from a shelf. Sensor ...................................................................................................................................... Use ...........................................................................................................................................

[2]
5

A company builds and sells furniture to customers. The company stores data about customers, their payment cards and their furniture orders in a database. The database, FURNITURE, has the following tables: CUSTOMER(CustomerID, Name, Phone) CUSTOMER_CARD_DATA(CardID, CustomerID, CardType, CardNumber, EndDate) ORDER(OrderID, CustomerID, TotalCost, Paid, OrderDate, Complete) ORDER_ITEM(OrderItemID, OrderID, Type, Height, Width, Depth, Details) The primary keys are underlined in each table. The attribute Complete in the table ORDER stores the Boolean value TRUE if the order has been built and FALSE if the order has not been built.

a

Complete the entity-relationship (E-R) diagram for the database.

[3]
b

Identify one attribute in the table CUSTOMER_CARD_DATA that could be a candidate key.

[1]
c

Identify two tables in the database that contain one or more foreign keys. Give one attribute that is a foreign key in each table.

[2]
d

Explain the reasons why the data in the table ORDER_ITEM cannot be stored in the table ORDER

[3]
e

Write an Structured Query Language (SQL) script to output the customer ID, the customer’s name and the total cost of the customer’s orders that have not been paid. The output of the total cost must have an appropriate title.

[4]
6

A programmer is buying a new computer.

a(i)

The programmer is considering the following two computers: Computer 1 Quad-core 2.2 GHz processor 16-bit architecture 1 GB Random Access Memory (RAM) 500 GB magnetic hard disk Computer 2 Dual-core 3.8 GHz processor 32-bit architecture 2 GB RAM 500 GB solid state drive (SSD) Computer 1 has a magnetic hard disk. Complete the description of the principal operation of a magnetic hard disk by writing the missing words. The magnetic hard disk has one or more ................................................... that can be magnetised. These are mounted on a ................................................... and rotate at high speed. A ................................................... is moved across the surface on an arm. When data is read, the changes in the ................................................... produce a change in the electric current.

[4]
a(ii)

The two computers have different amounts of RAM. Explain how different amounts of RAM affect the performance of a computer.

[3]
a(iii)

The two computers have different bus widths. Explain how different bus widths affect the performance of a computer.

[2]
b

Both computers have an Operating System (OS). Describe the purpose of an OS in a computer.

[5]
7

A banker stores personal data on their work computer.

a

The banker needs to transfer confidential data across the internet. Identify and describe one method of restricting the risks posed by an unauthorised person intercepting the data whilst it is being transferred across the internet. Method ...................................................................................................................................... Description ................................................................................................................................

[3]
b

The banker receives confidential data across the internet. The data includes a digital signature. Explain how a digital signature can make sure the data has not been changed during transmission.

[5]
c

The data that is transferred can also be verified using a checksum. Explain how data can be verified using a checksum.

[3]
8
a

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). Trace the program currently in memory using the following trace table.

[4]
b(i)

Write the bit manipulation instruction that can be used to set the least significant bit to 1 in an 8-bit register. All other bits must remain unchanged. The instruction needs to work on a register that contains any 8-bit binary number.

[1]
b(ii)

The ACC currently contains the following binary value. 0 1 0 1 0 1 0 1 Write the result after the instruction XOR &FE is run.

[1]
b(iii)

The ACC currently contains the following binary value. 0 1 1 0 1 0 1 1 Write the result after the instruction LSR #5 is run.

[1]

Mark scheme

9618/11 · May/June 2025

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1a · 2 marks

  • 1 mark

    X = Q AND (NOT P OR R)

  • 1 mark

    Y = S XOR (Q NOR R)

1b · 2 marks

  • 1 mark

    1 mark for first 4 rows (1, 1, 0, 1)

  • 1 mark

    1 mark for second 4 rows (0, 0, 1, 1)

2a · 4 marks

  • 1 mark

    Video is transmitted continuously

  • 1 mark

    as a series of bits

  • 1 mark

    The video is uploaded to a media server

  • 1 mark

    The users download from the media server

  • 1 mark

    On download, the media server sends the data to a buffer on the user's device

  • 1 mark

    buffer is used when there is a difference in speed between transmission and receipt

  • 1 mark

    Buffer stores data from server until recipient can receive it

  • 1 mark

    Recipient views bit stream from the buffer

2b(i) · 4 marks

  • 1 mark

    Video is data-intensive

  • 1 mark

    The file size needs reducing in order to

  • 1 mark

    reduce the amount of bandwidth used

  • 1 mark

    and reduce buffering

  • 1 mark

    This means people are not behind in the conversation

  • 1 mark

    and people with lower bandwidth can still take part

2b(ii) · 3 marks

  • 1 mark

    Reduces file size more than lossless

  • 1 mark

    so significantly less bandwidth / data is needed

  • 1 mark

    so buffering is reduced even more than with lossless

  • 1 mark

    Data can be removed which cannot be seen

  • 1 mark

    reducing quality without impacting experience

  • 1 mark

    for example, because resolution of video can be reduced // sample rate of audio can be reduced

2c · 2 marks

  • 1 mark

    modems: Converts digital data into analogue for transmission down phone lines // Converts analogue data into digital after transmission down phone lines

  • 1 mark

    dedicated lines: Used to provide a direct / private connection which therefore provides faster transmission

3a · 3 marks

  • 1 mark

    The term for the smallest element that makes up an image.: pixel

  • 1 mark

    The largest number of different colours that can be represented with a bit depth of 8 bits.: 256 // 28

  • 1 mark

    The term for the dots per inch (dpi) when an image is displayed.: Screen resolution

3b(i) · 2 marks

  • 1 mark

    A wider range of characters can be represented

  • 1 mark

    so characters from more languages can be represented

  • 1 mark

    and symbols such as emojis can be used

3b(ii) · 1 mark

  • 1 mark

    10,094

3b(iii) · 1 mark

  • 1 mark

    8,512

4a · 4 marks

  • 1 mark

    Uses image recognition / facial recognition

  • 1 mark

    Measures the distance between facial features of the customer

  • 1 mark

    and stores the values in a database of user information

  • 1 mark

    An image is captured using the digital camera

  • 1 mark

    the AI identifies that the image is a face

  • 1 mark

    by analysing the pixels to find patterns

  • 1 mark

    the distance between features is calculated and compared to those in database

4b · 2 marks

  • 1 mark

    Pressure: Detects when the pressure of an item is removed from a shelf / put back on a shelf

  • 1 mark

    Infrared: Detects when the beam is broken for an item removed / added

5a · 3 marks

  • 1 mark

    CUSTOMER to CUSTOMER_CARD_DATA 1-to-1 relationship

  • 1 mark

    CUSTOMER to ORDER 1-to-many relationship

  • 1 mark

    ORDER to ORDER_ITEM 1-to-many relationship

5b · 1 mark

  • 1 mark

    CardNumber

5c · 2 marks

  • 1 mark

    ORDER_ITEM: OrderID

  • 1 mark

    ORDER: CustomerID

  • 1 mark

    CUSTOMER_CARD_DATA: CustomerID

5d · 3 marks

  • 1 mark

    Each order would only be able to have one item

  • 1 mark

    or the database would not be normalised

  • 1 mark

    it would not be in 1NF

  • 1 mark

    due to repeated groups of attributes

  • 1 mark

    in the ORDER table

5e · 4 marks

  • 1 mark

    Selecting the customer ID, customer name and sum of TotalCost with appropriate identifier

  • 1 mark

    FROM clause with suitable join of tables (ON or WHERE)

  • 1 mark

    ORDER.Paid = FALSE condition (with correct key word)

  • 1 mark

    GROUP BY condition

6a(i) · 4 marks

  • 1 mark

    platters

  • 1 mark

    spindle

  • 1 mark

    read/write head

  • 1 mark

    magnetic field

6a(ii) · 3 marks

  • 1 mark

    More RAM means more currently running data and instructions can be stored

  • 1 mark

    without needing to use virtual memory

  • 1 mark

    without having to fetch the data from secondary storage first

  • 1 mark

    which has a slower access time

  • 1 mark

    Less latency / delay waiting for instructions / data

6a(iii) · 2 marks

  • 1 mark

    Wider data bus means more data can be transferred between components at a time

  • 1 mark

    there is less delay / latency when fetching data for a running process

  • 1 mark

    Wider address bus means larger memory addresses can be used

  • 1 mark

    allowing more memory locations to be accessed directly

  • 1 mark

    so less likely to run out of memory

6b · 5 marks

  • 1 mark

    To provide a user interface

  • 1 mark

    so that the user is able to communicate with the hardware

  • 1 mark

    To manage memory

  • 1 mark

    so that data can be stored and accessed

  • 1 mark

    and multitasking is possible

  • 1 mark

    To manage files

  • 1 mark

    allowing the user to create, edit, update and delete files and folders

  • 1 mark

    To manage inputs and outputs from hardware/peripherals

  • 1 mark

    To handle processes

  • 1 mark

    to make sure each process has fair access

7a · 3 marks

  • 1 mark

    Method: Encryption

  • 1 mark

    Description: Data is encoded/scrambled using a key to create cipher text

  • 1 mark

    Description: if intercepted it cannot be understood

  • 1 mark

    Description: without being decrypted using a key

7b · 5 marks

  • 1 mark

    The sender hashes the document / message

  • 1 mark

    to produce a digest

  • 1 mark

    The sender encrypts the digest to create the digital signature

  • 1 mark

    The message and the signature are sent to the banker / receiver

  • 1 mark

    The receiver decrypts the signature to reproduce the digest

  • 1 mark

    The receiver uses the same hashing algorithm on the document received to produce a second digest

  • 1 mark

    The receiver compares this digest with the one from the digital signature

  • 1 mark

    If both of the receiver’s digests are the same the document has not changed

7c · 3 marks

  • 1 mark

    The data is put through an algorithm to create a checksum value

  • 1 mark

    The data and checksum are sent to the receiver

  • 1 mark

    The receiver performs the same algorithm on the data

  • 1 mark

    if both checksums match the data is verified

8a · 4 marks

  • 1 mark

    Rows 200-201: ACC = 8 then 9

  • 1 mark

    Row 202: Address 83 = 9

  • 1 mark

    Rows 206-207: ACC = 9 then 19

  • 1 mark

    Row 210: Address 81 = 19

8b(i) · 1 mark

  • 1 mark

    OR B0000 0001 // OR #1 // OR &1

8b(ii) · 1 mark

  • 1 mark

    1010 1011

8b(iii) · 1 mark

  • 1 mark

    0000 0011

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