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Worked solutions

IB Computer Science SL · Paper 1

Computer Science, Standard Level

Session: November 2015
Marks: 70
Duration: 1 hour 30 min
Calculator: Not allowed
Questions: 9

Keep your copy of the paper open alongside. We don't reproduce the questions: each part below is labelled to match the November 2015 global paper, which your school or the IB can provide.

Practice mode

Hide our working until you've had a go.

Questions 1–6 · 25 marks

Question 1

3 marks

System usability definition and accessibility techniques

System fundamentals

(a)

1 mark

Define usability in software systems:
Usability refers to the quality of a system that makes it easy to learn, intuitive to navigate, and efficient for users to accomplish their goals effectively.

Mentor tip

Define usability focusing on simplicity, ergonomics, user-friendliness, and meeting user requirements.

(b)

2 marks

Identify two accessibility features:
1. Screen readers and speech synthesis (text-to-speech) to convey interface elements auditorily to visually impaired users.
2. Speech recognition input (voice control) to enable hands-free interaction for users with motor control or physical mobility impairments.

Mentor tip

Give two concrete accessibility provisions such as voice recognition, text-to-speech, touch screens, or braille keyboards.

Question 2

4 marks

VPN technologies for secure remote access

Networks

(a)

4 marks

Explain tunneling protocols:
1. Tunneling protocols encapsulate internal private network packets inside standard internet IP packets, establishing a secure logical connection across public communication links.
Explain encryption protocols:
2. Strong cryptographic protocols (such as IPsec or SSL/TLS) encrypt all packet payloads. If intercepted, third parties cannot decipher or tamper with the data.
Explain secure VPN gateway connectivity:
3. The corporate VPN gateway authenticates the salesperson's credentials and decrypts inbound traffic, granting seamless access to internal company servers as if locally connected.

Mentor tip

Detail tunneling protocols (packet encapsulation), encryption standards (such as IPsec to prevent eavesdropping), and secure gateway connectivity.

Question 3

3 marks

Truth table for compound Boolean expression

Computer organisation

(a)

3 marks

Analyze the compound expression:
Expression: $(A \land B) NOR C$ .
Compute intermediate term $X = A \land B$ :
$X = 1$ only when $A = 1$ and $B = 1$ ; otherwise $X = 0$ .
Evaluate NOR operation with $C$ :
Output is 1 only when BOTH $X = 0$ and $C = 0$ :
1. For $A = 0, B = 0, C = 0$ : $X = 0, C = 0 ⟹ 0 NOR 0 = 1$ .
2. For $A = 0, B = 0, C = 1$ : $X = 0, C = 1 ⟹ 0 NOR 1 = 0$ .
3. For $A = 0, B = 1, C = 0$ : $X = 0, C = 0 ⟹ 0 NOR 0 = 1$ .
4. For $A = 0, B = 1, C = 1$ : $X = 0, C = 1 ⟹ 0 NOR 1 = 0$ .
5. For $A = 1, B = 0, C = 0$ : $X = 0, C = 0 ⟹ 0 NOR 0 = 1$ .
6. For $A = 1, B = 0, C = 1$ : $X = 0, C = 1 ⟹ 0 NOR 1 = 0$ .
7. For $A = 1, B = 1, C = 0$ : $X = 1, C = 0 ⟹ 1 NOR 0 = 0$ .
8. For $A = 1, B = 1, C = 1$ : $X = 1, C = 1 ⟹ 1 NOR 1 = 0$ .

A 00001111 B 00110011 C 01010101 A \land B 00000011 (A \land B) NOR C 10101000

Mentor tip

Output is 1 only when C is 0 and (A AND B) is 0.

Question 4

6 marks

Software documentation types and user training methods

System fundamentals

(a)

4 marks

Type 1 - Technical documentation:
Description: Intended for IT technicians and system administrators, describing hardware requirements, network configuration, operating system dependencies, database schemas, and installation/maintenance steps.
Type 2 - User documentation:
Description: Intended for hotel staff and daily end-users, providing task-oriented tutorials, explanations of system features (such as room booking and checkout), FAQ sections, and error resolution guides.

Mentor tip

Describe technical documentation (installation, hardware specs, maintenance) and user documentation (user manual, feature guides, how-to instructions).

(b)

2 marks

State two user training delivery methods:
1. Instructor-led formal classroom training sessions / structured hands-on workshops.
2. Self-paced interactive online tutorials or remote computer-based training modules.

Mentor tip

State two delivery approaches such as instructor-led classroom sessions, self-paced online courses, or one-on-one workplace shadowing.

Question 5

4 marks

Network client-server model and external threat mitigation

Networks

(a)

1 mark

Define server in network infrastructure:
A server is a central host computer or software system that stores centralized files, manages user permissions, and provides shared network resources or services to connected client machines.

Mentor tip

Highlight that a server acts as a central repository for shared files, services, and applications across network clients.

(b)

1 mark

Identify network clients in the school setup:
The client machines are the individual workstation computers, student laptops, or shared network printers requesting services from the central server.

Mentor tip

Name the user workstation computers or network printer that interact with the central server.

(c)

2 marks

Identify an external security threat (Part i - 1 mark):
Malicious code intrusions such as computer viruses, spyware, or unauthorized remote infiltration by external hackers.
State a protective countermeasure (Part ii - 1 mark):
Install and continuously update anti-malware/antivirus software on all workstations and deploy an active network firewall to inspect and block unauthorized traffic.

Mentor tip

Pair a digital cyber-threat (viruses/spyware/hackers) with an appropriate countermeasure (firewall or antivirus software).

Question 6

5 marks

Algorithmic flaw analysis in iterative digit extraction

Computational thinking, problem-solving and programming

(a)

2 marks

Analyze loop execution state:
The loop condition tests `(N > 0) and (EVEN = true)`.
Identify why the algorithm fails to yield the correct result:
The value of $N$ is never reduced or updated within the loop body. If the initial least-significant digit is even, `EVEN` remains true and $N$ remains unchanged, causing an infinite loop that never terminates.

Mentor tip

Explain that N is never decremented or divided inside the loop, resulting in an infinite loop.

(b)

3 marks

Specify the required modification:
To examine each subsequent digit, $N$ must undergo integer division by 10 on each iteration.
Provide exact algorithmic placement:
Insert the statement `N = N div 10` inside the `while` loop body, placed directly after the `if` statement block so that each pass strips the inspected digit.

N = N div 10

Mentor tip

Add `N = N div 10` inside the while loop body following the if statement.

Questions 7–9 · 45 marks

Question 7

15 marks

System analysis, stakeholder engagement, and deployment strategies

System fundamentals

(a)

5 marks

Identify distinct user classes (Part i - 2 marks):
1. Frontline shop sales assistants and administrative office clerks.
2. The shop manager or business owner (supervisory management).
Explain stakeholder roles in development (Part ii - 3 marks):
1. Requirements gathering: Staff explain operational pain points, inventory workflows, and customer checkout procedures during initial interviews.
2. Prototype evaluation: Staff test early software iterations and provide constructive feedback regarding interface layout and efficiency.
3. Operational sign-off testing: End users validate final builds against realistic test cases to ensure the new system correctly handles daily business tasks before full launch.

Mentor tip

For (i) specify distinct staff categories (shop assistants, office clerks, managers). For (ii) describe user roles across requirements specification, prototype feedback, and operational sign-off testing.

(b)

2 marks

Explain utility of multiple prototypes:
Developing multiple prototypes allows managers and staff to compare contrasting interface layouts and operational workflows, choosing the optimal balance of speed, usability, and functionality before substantial code is finalized.

Mentor tip

Developing multiple prototypes offers comparative design options and reduces the risk of committing to a flawed interface.

(c)

4 marks

Problem 1 - Incompatible data formats and field schemas:
The legacy system may organize product IDs, pricing formats, or address fields differently, risking data truncation, type errors, or loss of information during automated migration.
Problem 2 - Non-unique or duplicate records:
The legacy dataset may lack unique constraint enforcement, resulting in duplicate customer or inventory records that violate relational integrity rules in the new database.

Mentor tip

Give two concrete migration issues such as schema/data type mismatches, non-unique/colliding primary keys, or data encoding discrepancies.

(d)

4 marks

Define parallel running (Part i - 2 marks):
Parallel running is a deployment strategy where both the legacy computer system and the newly developed system operate simultaneously on identical live business data for a defined transition period.
Explain reason for selecting parallel running over direct changeover (Part ii - 2 marks):
Risk mitigation: If unexpected critical bugs, data corruption, or system crashes occur in the new system, the legacy system continues to run uninterrupted as a fallback, preventing catastrophic business stoppage.

Mentor tip

Define parallel running as simultaneous operation of old and new systems, and explain the safety buffer / risk mitigation advantage over sudden direct cutover.

Question 8

15 marks

CPU registers, memory addressing, operating systems, and CPU datapath

Computer organisation

(a)

1 mark

Determine bit length per memory location:
Each memory word contains 8 hexadecimal digits (e.g., `00EF1079`).
Each hexadecimal digit corresponds to 4 binary bits:
$8 hex digits \times 4 bits = 32 bits$ .

8 \times 4 = 32 bits

Mentor tip

8 hexadecimal characters = 32 bits.

(b)

1 mark

Determine address size in bytes:
Each address consists of 4 hexadecimal digits (e.g., `1000`).
$4 hex digits \times 4 bits = 16 bits = 2 bytes$ .

\frac{4 \times 4 bits}{8 bits/byte} = 2 bytes

Mentor tip

4 hex digits = 16 bits = 2 bytes.

(c)

4 marks

Function of the Memory Address Register (MAR) (Part i - 2 marks):
The MAR holds the physical RAM address currently being targeted by the CPU for a memory read or write cycle, transmitting this address along the address bus.
Function of the Memory Data Register (MDR) (Part ii - 2 marks):
The MDR temporarily holds the data word or instruction fetched from RAM across the data bus, or holds data staged to be written into RAM.

Mentor tip

State that MAR holds memory addresses while MDR holds the fetched data or instruction contents.

(d)

3 marks

Two core functions of the operating system (Part i - 2 marks):
1. Memory management (allocating RAM space to concurrent processes and managing paging/virtual memory).
2. Process scheduling and resource allocation (controlling CPU time distribution and handling interrupts).
Storage location of the OS when powered off (Part ii - 1 mark):
Non-volatile secondary storage (hard disk drive, solid-state drive, or ROM).

Mentor tip

Name two core OS functions (memory management, process scheduling, file system) and state that it resides on secondary storage (hard drive/SSD/ROM) when powered off.

(e)

6 marks

CPU structure and data flow (Part i - 4 marks):
The central processing unit contains three core sub-units:
1. Control Unit (CU): Interprets instructions and generates control timing signals.
2. Arithmetic and Logic Unit (ALU): Performs arithmetic calculations and logical comparisons.
3. Registers (Program Counter, MAR, MDR, Accumulator): Store intermediate addresses and operands.
Data flows from RAM into the MDR via the data bus, transfers into the ALU for computation, and results are stored in the Accumulator or written back via the MDR.
Component performing instruction decoding (Part ii - 1 mark):
Control Unit (CU).
Component executing the instruction (Part iii - 1 mark):
Arithmetic and Logic Unit (ALU).

Mentor tip

Diagram/describe the CU, ALU, registers, and internal buses. Attribute decoding to the CU and execution to the ALU.

Question 9

15 marks

Parallel array lookup, averaging, and intersection search

Computational thinking, problem-solving and programming

(a)

1 mark

Query price from parallel arrays:
Given table entry at index 2: `Product_ID[2] = Jelly-1Q` corresponds directly to `Unit_Price[2] = 16.30`.
Price: 16.30.

Unit_Price [2] = 16.30

Mentor tip

Directly locate index [2] in the Unit_Price array.

(b)

3 marks

Explain average calculation algorithm:
1. Initialize an accumulator variable `SUM = 0`.
2. Iterate through all 20 elements of the `Unit_Price` array using a loop from index 0 to 19, adding each array value to `SUM`.
3. Compute the arithmetic mean by dividing `SUM` by the total number of products (20), then return or output the average.

AVERAGE = \frac{\sum _{i = 0}^{19} Unit_Price [ i ]}{20}

Mentor tip

Initialize sum to 0, loop through all 20 elements accumulating each price, and divide sum by 20.

(c)

6 marks

Construct linear search algorithm:
1. Prompt for target product identifier input from user: input TARGET_ID.
2. Initialize loop index `K = 0` and boolean flag `FOUND = false`.
3. Loop while `K < 20` and `NOT FOUND`:
If `Product_ID[K] == TARGET_ID` then:
FOUND = true
PRICE = Unit_Price[K]
End if
K = K + 1
End loop.
4. Output result based on search status:
If FOUND then:
output "The price is ", PRICE
Else:
output TARGET_ID, " does not appear on the list of product numbers"
End if.

Mentor tip

Use a boolean flag to terminate early upon match, and output either the found price or an appropriate not-found message.

(d)

5 marks

Maximum number of common IDs (Part i - 1 mark):
Warehouse One stocks 15 items and Warehouse Two stocks 10 items. The maximum possible size of their set intersection cannot exceed the smaller array size: $min (15, 10) = 10$ .
Algorithm to find common product IDs (Part ii - 4 marks):
1. Initialize index pointer for array Three: `Z = 0`.
2. Outer loop across Warehouse One items: loop K from 0 to 14.
3. Inner loop across Warehouse Two items: loop J from 0 to 9.
4. Compare identifiers:
If `One[K] == Two[J]` then:
Three[Z] = One[K]
Z = Z + 1
End if.
5. End inner and outer loops.

max (∣ One \cap Two ∣) = min (15, 10) = 10

Mentor tip

Maximum intersection is 10 (size of smaller warehouse). Use nested loops over arrays One and Two, adding matching elements to Three at index Z.

Our analysis

Where the marks are

Each part sorted by the topic it mostly tests. System fundamentals carries the most marks on this paper.

System fundamentals24 marks · 34%
Q1, Q4, Q7
Computational thinking, problem-solving and programming20 marks · 29%
Q6, Q9
Computer organisation18 marks · 26%
Q3, Q8
Networks8 marks · 11%
Q2, Q5

Mentor insights

Traps to watch for

01
NOR gate truth table truth condition · Q3
(A and B) NOR C is 1 only when (A and B) is 0 AND C is 0. Whenever C is 1, the result is immediately 0.
02
Termination condition in while loops inspecting digits · Q6
Omitting the division step N = N div 10 leaves N unchanged on every loop cycle, creating an infinite loop for any number whose first digit is even.
03
Maximum common items between two arrays · Q9
The intersection between two sets cannot exceed the cardinality of the smaller set; with warehouses of sizes 15 and 10, the maximum possible common items is exactly 10.

Solutions and tips are GeorgeTheTutor's own; the questions are not reproduced here. Not affiliated with or endorsed by the International Baccalaureate Organization.

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Worked solutions

IB Computer Science SL · Paper 1

Computer Science, Standard Level

Session: November 2015
Marks: 70
Duration: 1 hour 30 min
Calculator: Not allowed
Questions: 9

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9

Keep your copy of the paper open alongside. We don't reproduce the questions: each part below is labelled to match the November 2015 global paper, which your school or the IB can provide.

Practice mode

Hide our working until you've had a go.

Questions 1–6 · 25 marks

Question 1

3 marks

System usability definition and accessibility techniques

System fundamentals

(a)

1 mark

Define usability in software systems:
Usability refers to the quality of a system that makes it easy to learn, intuitive to navigate, and efficient for users to accomplish their goals effectively.

Mentor tip

Define usability focusing on simplicity, ergonomics, user-friendliness, and meeting user requirements.

(b)

2 marks

Identify two accessibility features:
1. Screen readers and speech synthesis (text-to-speech) to convey interface elements auditorily to visually impaired users.
2. Speech recognition input (voice control) to enable hands-free interaction for users with motor control or physical mobility impairments.

Mentor tip

Give two concrete accessibility provisions such as voice recognition, text-to-speech, touch screens, or braille keyboards.

Question 2

4 marks

VPN technologies for secure remote access

Networks

(a)

4 marks

Explain tunneling protocols:
1. Tunneling protocols encapsulate internal private network packets inside standard internet IP packets, establishing a secure logical connection across public communication links.
Explain encryption protocols:
2. Strong cryptographic protocols (such as IPsec or SSL/TLS) encrypt all packet payloads. If intercepted, third parties cannot decipher or tamper with the data.
Explain secure VPN gateway connectivity:
3. The corporate VPN gateway authenticates the salesperson's credentials and decrypts inbound traffic, granting seamless access to internal company servers as if locally connected.

Mentor tip

Detail tunneling protocols (packet encapsulation), encryption standards (such as IPsec to prevent eavesdropping), and secure gateway connectivity.

Question 3

3 marks

Truth table for compound Boolean expression

Computer organisation

(a)

3 marks

Analyze the compound expression:
Expression: $(A \land B) NOR C$ .
Compute intermediate term $X = A \land B$ :
$X = 1$ only when $A = 1$ and $B = 1$ ; otherwise $X = 0$ .
Evaluate NOR operation with $C$ :
Output is 1 only when BOTH $X = 0$ and $C = 0$ :
1. For $A = 0, B = 0, C = 0$ : $X = 0, C = 0 ⟹ 0 NOR 0 = 1$ .
2. For $A = 0, B = 0, C = 1$ : $X = 0, C = 1 ⟹ 0 NOR 1 = 0$ .
3. For $A = 0, B = 1, C = 0$ : $X = 0, C = 0 ⟹ 0 NOR 0 = 1$ .
4. For $A = 0, B = 1, C = 1$ : $X = 0, C = 1 ⟹ 0 NOR 1 = 0$ .
5. For $A = 1, B = 0, C = 0$ : $X = 0, C = 0 ⟹ 0 NOR 0 = 1$ .
6. For $A = 1, B = 0, C = 1$ : $X = 0, C = 1 ⟹ 0 NOR 1 = 0$ .
7. For $A = 1, B = 1, C = 0$ : $X = 1, C = 0 ⟹ 1 NOR 0 = 0$ .
8. For $A = 1, B = 1, C = 1$ : $X = 1, C = 1 ⟹ 1 NOR 1 = 0$ .

A 00001111 B 00110011 C 01010101 A \land B 00000011 (A \land B) NOR C 10101000

Mentor tip

Output is 1 only when C is 0 and (A AND B) is 0.

Question 4

6 marks

Software documentation types and user training methods

System fundamentals

(a)

4 marks

Type 1 - Technical documentation:
Description: Intended for IT technicians and system administrators, describing hardware requirements, network configuration, operating system dependencies, database schemas, and installation/maintenance steps.
Type 2 - User documentation:
Description: Intended for hotel staff and daily end-users, providing task-oriented tutorials, explanations of system features (such as room booking and checkout), FAQ sections, and error resolution guides.

Mentor tip

Describe technical documentation (installation, hardware specs, maintenance) and user documentation (user manual, feature guides, how-to instructions).

(b)

2 marks

State two user training delivery methods:
1. Instructor-led formal classroom training sessions / structured hands-on workshops.
2. Self-paced interactive online tutorials or remote computer-based training modules.

Mentor tip

State two delivery approaches such as instructor-led classroom sessions, self-paced online courses, or one-on-one workplace shadowing.

Question 5

4 marks

Network client-server model and external threat mitigation

Networks

(a)

1 mark

Define server in network infrastructure:
A server is a central host computer or software system that stores centralized files, manages user permissions, and provides shared network resources or services to connected client machines.

Mentor tip

Highlight that a server acts as a central repository for shared files, services, and applications across network clients.

(b)

1 mark

Identify network clients in the school setup:
The client machines are the individual workstation computers, student laptops, or shared network printers requesting services from the central server.

Mentor tip

Name the user workstation computers or network printer that interact with the central server.

(c)

2 marks

Identify an external security threat (Part i - 1 mark):
Malicious code intrusions such as computer viruses, spyware, or unauthorized remote infiltration by external hackers.
State a protective countermeasure (Part ii - 1 mark):
Install and continuously update anti-malware/antivirus software on all workstations and deploy an active network firewall to inspect and block unauthorized traffic.

Mentor tip

Pair a digital cyber-threat (viruses/spyware/hackers) with an appropriate countermeasure (firewall or antivirus software).

Question 6

5 marks

Algorithmic flaw analysis in iterative digit extraction

Computational thinking, problem-solving and programming

(a)

2 marks

Analyze loop execution state:
The loop condition tests `(N > 0) and (EVEN = true)`.
Identify why the algorithm fails to yield the correct result:
The value of $N$ is never reduced or updated within the loop body. If the initial least-significant digit is even, `EVEN` remains true and $N$ remains unchanged, causing an infinite loop that never terminates.

Mentor tip

Explain that N is never decremented or divided inside the loop, resulting in an infinite loop.

(b)

3 marks

Specify the required modification:
To examine each subsequent digit, $N$ must undergo integer division by 10 on each iteration.
Provide exact algorithmic placement:
Insert the statement `N = N div 10` inside the `while` loop body, placed directly after the `if` statement block so that each pass strips the inspected digit.

N = N div 10

Mentor tip

Add `N = N div 10` inside the while loop body following the if statement.

Questions 7–9 · 45 marks

Question 7

15 marks

System analysis, stakeholder engagement, and deployment strategies

System fundamentals

(a)

5 marks

Identify distinct user classes (Part i - 2 marks):
1. Frontline shop sales assistants and administrative office clerks.
2. The shop manager or business owner (supervisory management).
Explain stakeholder roles in development (Part ii - 3 marks):
1. Requirements gathering: Staff explain operational pain points, inventory workflows, and customer checkout procedures during initial interviews.
2. Prototype evaluation: Staff test early software iterations and provide constructive feedback regarding interface layout and efficiency.
3. Operational sign-off testing: End users validate final builds against realistic test cases to ensure the new system correctly handles daily business tasks before full launch.

Mentor tip

(b)

2 marks

Explain utility of multiple prototypes:
Developing multiple prototypes allows managers and staff to compare contrasting interface layouts and operational workflows, choosing the optimal balance of speed, usability, and functionality before substantial code is finalized.

Mentor tip

Developing multiple prototypes offers comparative design options and reduces the risk of committing to a flawed interface.

(c)

4 marks

Problem 1 - Incompatible data formats and field schemas:
The legacy system may organize product IDs, pricing formats, or address fields differently, risking data truncation, type errors, or loss of information during automated migration.
Problem 2 - Non-unique or duplicate records:
The legacy dataset may lack unique constraint enforcement, resulting in duplicate customer or inventory records that violate relational integrity rules in the new database.

Mentor tip

Give two concrete migration issues such as schema/data type mismatches, non-unique/colliding primary keys, or data encoding discrepancies.

(d)

4 marks

Define parallel running (Part i - 2 marks):
Parallel running is a deployment strategy where both the legacy computer system and the newly developed system operate simultaneously on identical live business data for a defined transition period.
Explain reason for selecting parallel running over direct changeover (Part ii - 2 marks):
Risk mitigation: If unexpected critical bugs, data corruption, or system crashes occur in the new system, the legacy system continues to run uninterrupted as a fallback, preventing catastrophic business stoppage.

Mentor tip

Define parallel running as simultaneous operation of old and new systems, and explain the safety buffer / risk mitigation advantage over sudden direct cutover.

Question 8

15 marks

CPU registers, memory addressing, operating systems, and CPU datapath

Computer organisation

(a)

1 mark

Determine bit length per memory location:
Each memory word contains 8 hexadecimal digits (e.g., `00EF1079`).
Each hexadecimal digit corresponds to 4 binary bits:
$8 hex digits \times 4 bits = 32 bits$ .

8 \times 4 = 32 bits

Mentor tip

8 hexadecimal characters = 32 bits.

(b)

1 mark

Determine address size in bytes:
Each address consists of 4 hexadecimal digits (e.g., `1000`).
$4 hex digits \times 4 bits = 16 bits = 2 bytes$ .

\frac{4 \times 4 bits}{8 bits/byte} = 2 bytes

Mentor tip

4 hex digits = 16 bits = 2 bytes.

(c)

4 marks

Function of the Memory Address Register (MAR) (Part i - 2 marks):
The MAR holds the physical RAM address currently being targeted by the CPU for a memory read or write cycle, transmitting this address along the address bus.
Function of the Memory Data Register (MDR) (Part ii - 2 marks):
The MDR temporarily holds the data word or instruction fetched from RAM across the data bus, or holds data staged to be written into RAM.

Mentor tip

State that MAR holds memory addresses while MDR holds the fetched data or instruction contents.

(d)

3 marks

Two core functions of the operating system (Part i - 2 marks):
1. Memory management (allocating RAM space to concurrent processes and managing paging/virtual memory).
2. Process scheduling and resource allocation (controlling CPU time distribution and handling interrupts).
Storage location of the OS when powered off (Part ii - 1 mark):
Non-volatile secondary storage (hard disk drive, solid-state drive, or ROM).

Mentor tip

Name two core OS functions (memory management, process scheduling, file system) and state that it resides on secondary storage (hard drive/SSD/ROM) when powered off.

(e)

6 marks

CPU structure and data flow (Part i - 4 marks):
The central processing unit contains three core sub-units:
1. Control Unit (CU): Interprets instructions and generates control timing signals.
2. Arithmetic and Logic Unit (ALU): Performs arithmetic calculations and logical comparisons.
3. Registers (Program Counter, MAR, MDR, Accumulator): Store intermediate addresses and operands.
Data flows from RAM into the MDR via the data bus, transfers into the ALU for computation, and results are stored in the Accumulator or written back via the MDR.
Component performing instruction decoding (Part ii - 1 mark):
Control Unit (CU).
Component executing the instruction (Part iii - 1 mark):
Arithmetic and Logic Unit (ALU).

Mentor tip

Diagram/describe the CU, ALU, registers, and internal buses. Attribute decoding to the CU and execution to the ALU.

Question 9

15 marks

Parallel array lookup, averaging, and intersection search

Computational thinking, problem-solving and programming

(a)

1 mark

Query price from parallel arrays:
Given table entry at index 2: `Product_ID[2] = Jelly-1Q` corresponds directly to `Unit_Price[2] = 16.30`.
Price: 16.30.

Unit_Price [2] = 16.30

Mentor tip

Directly locate index [2] in the Unit_Price array.

(b)

3 marks

Explain average calculation algorithm:
1. Initialize an accumulator variable `SUM = 0`.
2. Iterate through all 20 elements of the `Unit_Price` array using a loop from index 0 to 19, adding each array value to `SUM`.
3. Compute the arithmetic mean by dividing `SUM` by the total number of products (20), then return or output the average.

AVERAGE = \frac{\sum _{i = 0}^{19} Unit_Price [ i ]}{20}

Mentor tip

Initialize sum to 0, loop through all 20 elements accumulating each price, and divide sum by 20.

(c)

6 marks

Construct linear search algorithm:
1. Prompt for target product identifier input from user: input TARGET_ID.
2. Initialize loop index `K = 0` and boolean flag `FOUND = false`.
3. Loop while `K < 20` and `NOT FOUND`:
If `Product_ID[K] == TARGET_ID` then:
FOUND = true
PRICE = Unit_Price[K]
End if
K = K + 1
End loop.
4. Output result based on search status:
If FOUND then:
output "The price is ", PRICE
Else:
output TARGET_ID, " does not appear on the list of product numbers"
End if.

Mentor tip

Use a boolean flag to terminate early upon match, and output either the found price or an appropriate not-found message.

(d)

5 marks

Maximum number of common IDs (Part i - 1 mark):
Warehouse One stocks 15 items and Warehouse Two stocks 10 items. The maximum possible size of their set intersection cannot exceed the smaller array size: $min (15, 10) = 10$ .
Algorithm to find common product IDs (Part ii - 4 marks):
1. Initialize index pointer for array Three: `Z = 0`.
2. Outer loop across Warehouse One items: loop K from 0 to 14.
3. Inner loop across Warehouse Two items: loop J from 0 to 9.
4. Compare identifiers:
If `One[K] == Two[J]` then:
Three[Z] = One[K]
Z = Z + 1
End if.
5. End inner and outer loops.

max (∣ One \cap Two ∣) = min (15, 10) = 10

Mentor tip

Maximum intersection is 10 (size of smaller warehouse). Use nested loops over arrays One and Two, adding matching elements to Three at index Z.

Our analysis

Where the marks are

Each part sorted by the topic it mostly tests. System fundamentals carries the most marks on this paper.

System fundamentals24 marks · 34%
Q1, Q4, Q7
Computational thinking, problem-solving and programming20 marks · 29%
Q6, Q9
Computer organisation18 marks · 26%
Q3, Q8
Networks8 marks · 11%
Q2, Q5

Mentor insights

Traps to watch for

01
NOR gate truth table truth condition · Q3
(A and B) NOR C is 1 only when (A and B) is 0 AND C is 0. Whenever C is 1, the result is immediately 0.
02
Termination condition in while loops inspecting digits · Q6
Omitting the division step N = N div 10 leaves N unchanged on every loop cycle, creating an infinite loop for any number whose first digit is even.
03
Maximum common items between two arrays · Q9
The intersection between two sets cannot exceed the cardinality of the smaller set; with warehouses of sizes 15 and 10, the maximum possible common items is exactly 10.

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