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A Level Computer Science 9618 Paper 31, Oct/Nov 2025

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9618/31 · Oct/Nov 2025

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1

The composite record data type, ClubMember, is defined in pseudocode as: TYPE ClubMember DECLARE Code : INTEGER DECLARE LastName : STRING DECLARE FirstName : STRING DECLARE Telephone : STRING DECLARE JoinDate : DATE DECLARE Fees : REAL DECLARE FeesPaid : BOOLEAN ENDTYPE

a(i)

Write the pseudocode statement to set up a variable for one record of the composite data type, ClubMember.

[1]
a(ii)

Write the pseudocode statements to assign the following values to the variable set up in part (a)(i): • 984632 to Code • TRUE to FeesPaid

[2]
b(i)

An enumerated data type, Activity, is required, so that a new field, Choice, can be added to the composite data type, ClubMember, to allow members to choose an activity. Write the pseudocode statement for the type declaration of Activity to hold the names of the available activities: Badminton, Football, Golf, Snooker, Swimming, Tennis.

[2]
b(ii)

Write the new pseudocode statement required to update the declaration of Choice in the definition of ClubMember.

[1]
2

Numbers are stored in a computer system using binary floating‑point representation with: • 12 bits for the mantissa • 4 bits for the exponent • two’s complement form for both the mantissa and the exponent.

a

Write the normalised floating‑point representation of the following positive binary number using this system. 0.00000001110101101

[2]
b

Calculate the normalised binary floating‑point representation of –76.1875 in this system. Show your working.

[4]
3
a

Explain why protocols are essential for communication between computer systems.

[2]
b

POP3 is an email communication protocol. Identify and describe two other communication protocols that are used when sending or receiving emails. Protocol 1 .................................................................................................................. Description ................................................................................................................ Protocol 2 .................................................................................................................. Description ................................................................................................................

[4]
c

Describe two ways in which packet switching ensures a complete message is received when passing messages across a network. 1 ................................................................................................................................ 2 ................................................................................................................................

[4]
4
a

A scheduling routine determines how processes are managed by the operating system. Identify two scheduling routines. 1 ................................................................................................................................ 2 ................................................................................................................................

[2]
b

Describe two ways in which the complexities of the computer hardware are hidden from the user. 1 ................................................................................................................................ 2 ................................................................................................................................

[4]
5
a

Identify two items commonly found within a digital certificate. 1 ................................................................................................................................ 2 ................................................................................................................................

[2]
b

Explain why a digital certificate is required to validate a digital signature.

[3]
6
Figure 1 of 2 for question 6
Figure 2 of 2 for question 6
a

The diagram shows a logic circuit. Complete the truth table for the given logic circuit. Show your working.

[3]
b(i)

Complete the Karnaugh map (K‑map) for the Boolean expression: A‾.B.C+A‾.B.C‾+A.B‾.C+A.B.C‾

[2]
b(ii)

Draw loop(s) around appropriate group(s) in the K‑map to produce an optimal sum‑of‑products.

[2]
b(iii)

Write the Boolean expression from your answer to part b(ii) as a simplified sum‑of‑products. Do not carry out any further simplification.

[2]
7
a

Identify one Artificial Intelligence (AI) algorithm to find the shortest distance between two points on a graph.

[1]
b

Describe Deep Learning.

[5]
8
a

Outline the purpose of lexical analysis during the compilation of a program.

[2]
b

Write the Reverse Polish Notation (RPN) for the given infix expression: (2 – 6) * (13 + 7) / 5

[2]
c

The RPN expression: d a b + * c a ‑ / is to be evaluated, where: a = 6, b = 12, c = 15 and d = 5. Show the changing contents of the stack as the RPN expression is evaluated.

[4]
9

A stack has been implemented using pseudocode to store a maximum of 100 string items using the global variables in the following table: Identifier | Data type | Description | Initialisation value Base | INTEGER | pointer for the bottom of the stack | 0 Top | INTEGER | pointer for the top of the stack | ‑1 StackArray | STRING | 1D array to implement the stack | [0:99] Max | INTEGER | maximum number of items in the stack | 100 The value of Top is incremented each time a data item is added to the stack and decremented every time a data item is removed.

a(i)

Complete the pseudocode for the function to remove a data item from the stack. FUNCTION Pop() ........................................................................................................... DECLARE DataItem : STRING DataItem ← "" IF .................................................................................................................... THEN DataItem ← ....................................................................................................... Top ← .................................................................................................. ELSE DataItem ← "You cannot remove data; the stack is empty" ENDIF ...................................................................................................................................... ENDFUNCTION

[5]
a(ii)

Write the pseudocode to output the data item removed from the stack with an appropriate message.

[1]
b

A stack is used to implement recursion. State the three essential features of recursion. 1 ................................................................................................................................ 2 ................................................................................................................................ 3 ................................................................................................................................

[3]
10

Explain what is meant by exception handling. Include an example of a possible cause of an exception in your answer. Explanation ....................................................................................................................................... Example ...........................................................................................................................................

[3]
11

The table shows assembly language instructions for a processor that has one register, the Accumulator (ACC). Instruction Label | Opcode | Operand | Explanation | LDM | #n | Load the number n to ACC | LDD | <address> | Load the contents of the location at the given address to the ACC | LDI | <address> | The address to be used is at the given address. Load the contents of this second address to the ACC | ADD | <address> | Add the contents of the given address to the ACC | SUB | <address> | Subtract the contents of the given address from the ACC | STO | <address> | Store the contents of the ACC at the given address <label>: | | <data> | Gives a symbolic address <label> to the memory location with contents <data> # denotes a denary number, e.g. #123 <label> can be used in place of <address>

a

Write assembly language code, using only the given instruction set to: • store the denary value 100 as a named constant • subtract the constant from the value contained in address 632 • store the result in variable Answer. Show the initialisation of the constant and Answer in the table provided.

[6]
b

The address 632 contains the value 45. State the value of Answer after the code described in part (a) has executed.

[1]

Mark scheme

9618/31 · Oct/Nov 2025

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1a(i) · 1 mark

  • 1 mark

    DECLARE Member1 : ClubMember

1a(ii) · 2 marks

  • 1 mark

    Member1.Code  984632

  • 1 mark

    Member1.FeesPaid  TRUE

1b(i) · 2 marks

  • 1 mark

    TYPE Activity=

  • 1 mark

    (Badminton, Football, Golf, Snooker, Swimming, Tennis)

1b(ii) · 1 mark

  • 1 mark

    DECLARE Choice : Activity

2a · 2 marks

  • 1 mark

    Correct mantissa: 0 1 1 1 0 1 0 1 1 0 1 0

  • 1 mark

    Correct exponent: 1 0 0 1

2b · 4 marks

  • 1 mark

    correct method to find the binary number

  • 1 mark

    additional working towards binary number

  • 1 mark

    correct use of exponent (movement of binary point by 7 places // 1.011001111 01 x 2^7)

  • 1 mark

    correct answer in the space provided: Mantissa 1 0 1 1 0 0 1 1 1 1 0 1, Exponent 0 1 1 1

3a · 2 marks

  • 1 mark

    Protocols set a standard for communication // Protocols establish a standard set of rules for communication

  • 1 mark

    Protocols enable compatibility between devices from different manufacturers/platforms

  • 1 mark

    Two devices wouldn’t be able to communicate/send messages to each other if they were using different protocols

3b · 4 marks

  • 1 mark

    SMTP

  • 1 mark

    a protocol used to send emails between mail servers // a protocol used to send emails from a computer to a mail server

  • 1 mark

    IMAP

  • 1 mark

    allows users to access/read their emails from any device without removing the message from the mail server // synchronises emails on any device

3c · 4 marks

  • 1 mark

    Packets checked at receiving end / on arrival

  • 1 mark

    … if packets arrive damaged or don’t arrive at all, a re-send request is sent

  • 1 mark

    Packets routed through different paths / sent individually

  • 1 mark

    … if a route is blocked, the packet is sent through a different route to ensure it arrives

  • 1 mark

    If the packet’s hop count is exceeded

  • 1 mark

    … the packet will be retired, which can generate a re-send request

4a · 2 marks

  • 1 mark

    Round robin

  • 1 mark

    Shortest job first

  • 1 mark

    First come first served

  • 1 mark

    Shortest remaining time

4b · 4 marks

  • 1 mark

    Provision of a User Interface // Provision of a Graphical User Interface

  • 1 mark

    Allows the user to interact with the computer in a more intuitive way // Icons and menus are used to control devices by simply ‘pointing and clicking’

  • 1 mark

    Use of device drivers

  • 1 mark

    Makes it easier to control peripherals such as printers within the operating system of the computer rather than on the separate device itself

  • 1 mark

    Device mapping

  • 1 mark

    Different devices (physical and virtual) are easy to identify on the network, check their status, or use

  • 1 mark

    The user interacts only with the Application / top layer (of the TCP/IP protocol suite)

  • 1 mark

    leaving the lower layers and their complexities hidden from the user

5a · 2 marks

  • 1 mark

    Name of certificate holder // Subject

  • 1 mark

    Serial number

  • 1 mark

    Version number

  • 1 mark

    Expiration date // Start date // Validity (not before/not after)

  • 1 mark

    Certificate holder’s public key // Subject public key

  • 1 mark

    Subject digital signature

  • 1 mark

    Certificate Issuer // Digital signature of CA

5b · 3 marks

  • 1 mark

    A digital certificate provides a public key

  • 1 mark

    … which validates the private key used to create the digital signature

  • 1 mark

    It makes a digital signature virtually impossible to spoof // Provides evidence of signer identity that the document was not altered and the signatures are valid

  • 1 mark

    Non repudiation.

6a · 3 marks

  • 1 mark

    working, (all four columns P, Q, R and S)

  • 1 mark

    first four rows of column Z

  • 1 mark

    second four rows of column Z

6b(i) · 2 marks

  • 2 marks

    Correct table entries: Row 0 = [0, 0, 1, 1], Row 1 = [0, 1, 0, 1] (Two marks if no errors present, One mark if only one error present)

6b(ii) · 2 marks

  • 1 mark

    Loop grouping cells (0,11) and (0,10)

  • 1 mark

    Loop grouping cells (0,10) and (1,10)

6b(iii) · 2 marks

  • 1 mark

    One correct Boolean term with a + / OR sign

  • 1 mark

    All Boolean terms and operators correct and no other terms present: Ā.B + B.C̄ + A.B̄.C

7a · 1 mark

  • 1 mark

    A* algorithm // Dijkstra’s algorithm

7b · 5 marks

  • 1 mark

    Deep learning is a branch of machine learning

  • 1 mark

    It makes use of artificial neural networks

  • 1 mark

    … to work in a similar manner to the human/biological brain // … neural networks can be trained to process data

  • 1 mark

    It is a structure consisting of many interconnected layers

  • 1 mark

    … input, hidden and output // the input layer feeds the first hidden layer, the last hidden layer feeds the output

  • 1 mark

    … gradually breaking down and analysing the data to find (hidden) patterns

  • 1 mark

    Deep leaning’s feature extraction/learning involves how to detect features/categories from data

  • 1 mark

    … and can involve different types of supervision

  • 1 mark

    It works well with large data sets

  • 1 mark

    Deep learning uses back propagation of errors to adjust parameters/weightings to refine its results / improve its accuracy.

8a · 2 marks

  • 1 mark

    To convert the high-level source code / program into a sequence of tokens

  • 1 mark

    … that can be sent to the parser for syntax analysis

  • 1 mark

    To create a symbol table

  • 1 mark

    To remove the unnecessary white space and comments from the code

8b · 2 marks

  • 1 mark

    2 6 –

  • 1 mark

    13 7 + * 5 /

8c · 4 marks

  • 1 mark

    Ring around stack state with 18 / 5

  • 1 mark

    Ring around stack state with 90

  • 1 mark

    Ring around stack state with 6 / 15 / 90

  • 1 mark

    Ring around final stack state with 10

9a(i) · 5 marks

  • 1 mark

    FUNCTION Pop() RETURNS STRING

  • 1 mark

    IF Top > –1 // Top >= Base THEN

  • 1 mark

    DataItem  StackArray[Top]

  • 1 mark

    Top  Top – 1

  • 1 mark

    DataItem  "You cannot remove data; the stack is empty"

  • 1 mark

    RETURN DataItem // StackArray[Top + 1]

9a(ii) · 1 mark

  • 1 mark

    OUTPUT "The data removed from the stack is ", Pop()

9b · 3 marks

  • 1 mark

    A recursive algorithm must call itself / have a general case

  • 1 mark

    It must have a base case / have a stopping condition

  • 1 mark

    It must change its state and move towards the base case

10 · 3 marks

  • 1 mark

    Exception handling is a process that responds to unwanted / unexpected events when a program runs

  • 1 mark

    … to prevent the program / computer from stopping unexpectedly

  • 1 mark

    Programming errors // User errors // Hardware failure // losing connection to a device such as a printer

11a · 6 marks

  • 1 mark

    LDM #100 seen

  • 1 mark

    Correct use of STO with labelled address (constant or answer)

  • 1 mark

    Correct use of LDD 632

  • 1 mark

    Correct use of SUB with labelled address (constant)

  • 1 mark

    Storing 100 at a labelled address away from the code

  • 1 mark

    Labelling both addresses away from the code.

11b · 1 mark

  • 1 mark

    –55

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  10. 10
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