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Worked solutions

IB Computer Science SL · Paper 1

Computer Science, Standard Level

Session: May 2015
Marks: 70
Duration: 1 hour 30 min
Calculator: Not allowed
Questions: 10

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

Practice mode

Hide our working until you've had a go.

Questions 1–7 · 25 marks

Question 1

4 marks

Truth table for compound Boolean expression

Computer organisation

(a)

4 marks

Analyze the Boolean expression:
Expression: $(A \lor B) \land (\neg C \lor B)$ .
Evaluate intermediate terms for all 8 combinations of inputs $(A, B, C)$ :
1. For $A = 0, B = 0, C = 0$ : $A \lor B = 0$ , $\neg C \lor B = 1 \lor 0 = 1$ . Final output: $0 \land 1 = 0$ .
2. For $A = 0, B = 0, C = 1$ : $A \lor B = 0$ , $\neg C \lor B = 0 \lor 0 = 0$ . Final output: $0 \land 0 = 0$ .
3. For $A = 0, B = 1, C = 0$ : $A \lor B = 1$ , $\neg C \lor B = 1 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .
4. For $A = 0, B = 1, C = 1$ : $A \lor B = 1$ , $\neg C \lor B = 0 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .
5. For $A = 1, B = 0, C = 0$ : $A \lor B = 1$ , $\neg C \lor B = 1 \lor 0 = 1$ . Final output: $1 \land 1 = 1$ .
6. For $A = 1, B = 0, C = 1$ : $A \lor B = 1$ , $\neg C \lor B = 0 \lor 0 = 0$ . Final output: $1 \land 0 = 0$ .
7. For $A = 1, B = 1, C = 0$ : $A \lor B = 1$ , $\neg C \lor B = 1 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .
8. For $A = 1, B = 1, C = 1$ : $A \lor B = 1$ , $\neg C \lor B = 0 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .

A 00001111 B 00110011 C 01010101 A \lor B 00111111 \neg C \lor B 10111011 (A \lor B) \land (\neg C \lor B) 00111011

Mentor tip

Recognize that whenever input B is 1, both OR clauses evaluate to 1, guaranteeing an output of 1 regardless of A or C.

Question 2

3 marks

Application and function of a virtual private network

Networks

(a)

3 marks

Outline a practical VPN scenario:
A remote employee working from home or travelling needs to connect securely to the organization's private corporate network.
Explain technical implementation:
1. The remote computer initiates an encrypted virtual tunnel over the unsecure public internet to the organization's VPN server.
2. The VPN encapsulates all transmitted packets with IPsec or SSL/TLS encryption, preventing unauthorized interception while allowing seamless access to restricted internal resources.

Mentor tip

State a valid use case (remote worker access) and elaborate on the creation of an encrypted communication tunnel over public infrastructure.

Question 3

2 marks

Sub-procedures as programmatic abstraction

Computational thinking, problem-solving and programming

(a)

2 marks

Define procedural abstraction:
A sub-procedure encapsulates a specific sub-task within a named block of code, exposing only a clear parameter interface while concealing its internal operational implementation details.
Explain how it functions as abstraction:
Callers invoke the sub-procedure by its identifier without needing to know or manage the low-level logic, loops, or internal variables executing inside it, thereby reducing mental complexity.

Mentor tip

Focus on hiding implementation complexity behind a reusable callable interface.

Question 4

4 marks

Algorithm tracing for perfect number verification

Computational thinking, problem-solving and programming

(a)

4 marks

Analyze algorithmic parameters:
Input: $N = 6, SUM = 0$ . The loop increments $COUNT$ from $1$ to $(N div 2) = 3$ .
Trace each iteration:
Iteration 1 (COUNT = 1): $6 mod 1 = 0$ (True). $SUM = 0 + 1 = 1$ .
Iteration 2 (COUNT = 2): $6 mod 2 = 0$ (True). $SUM = 1 + 2 = 3$ .
Iteration 3 (COUNT = 3): $6 mod 3 = 0$ (True). $SUM = 3 + 3 = 6$ .
Evaluate loop termination and output check:
Loop finishes as $COUNT$ completes value 3.
Condition check: $SUM = N ⟹ 6 = 6$ (True).
Output: "perfect".

COUNT 123 N (mod COUNT) = 0 True True True SUM 01366 SUM = N True Output "perfect"

Mentor tip

Record values after each loop step clearly in the trace table columns.

Question 5

4 marks

Hardware usability features of modern laptops

System fundamentals

(a)

4 marks

Feature 1 - High-resolution anti-glare display with scaling controls:
Usability impact: Provides clear visual contrast and adjustable font sizes, minimizing eyestrain and assisting users with visual impairments in diverse lighting conditions.
Feature 2 - Multi-touch touchpad with adjustable sensitivity and tactile feedback:
Usability impact: Enables precise cursor manipulation and customizable gestures (pinch-to-zoom, two-finger scrolling), accommodating users with motor skill variations or repetitive strain.

Mentor tip

Identify two distinct hardware usability characteristics and clearly explain how each accommodates varying user capabilities or ergonomics.

Question 6

2 marks

Software update notification mechanisms

System fundamentals

(a)

2 marks

Describe automatic update polling:
The client application contains a background service that queries the developer's update repository on application startup or via a scheduled timer.
Explain user notification delivery:
If a newer version hash is discovered, the program presents an in-app banner or pop-up notification prompting the user to install the patch immediately or view release notes.

Mentor tip

Outline both the detection method (startup query to update server) and presentation to the user (in-app pop-up or notification banner).

Question 7

6 marks

Project task sequencing, concurrency, and Gantt scheduling

System fundamentals

(a)

2 marks

Identify 4 sequential project phases:
1. Collect water samples from the four lakes.
2. Laboratory analysis of the water samples.
3. Write the scientific report.
4. Prepare the animated computer presentation.

Mentor tip

List the four tasks in logical chronological sequence from data collection to report and presentation preparation.

(b)

2 marks

Identify concurrent tasks:
"Write the scientific report" and "Prepare the animated computer presentation".
Explain concurrency mechanism:
Once the laboratory sample data is finalized, the 6 students can split into sub-teams: one group drafts the textual report while the other builds the animated slides simultaneously using the same shared dataset.

Mentor tip

Writing the report and creating the presentation can occur concurrently since different group members work simultaneously on shared analysis findings.

(c)

2 marks

Construct Gantt chart schedule representation:
Show sequential dependencies followed by parallel execution across phases:
Phase 1: Task 1 (Collect water samples).
Phase 2: Task 2 (Analyse water samples) begins only after Phase 1 finishes.
Phase 3: Task 3 (Write scientific report) and Task 4 (Prepare animated presentation) run concurrently in parallel.

Task 1. Collect samples 2. Analyse samples 3. Write report 4. Prepare presentation Phase 1 [■] Phase 2 [■] Phase 3 [■] [■]

Mentor tip

Ensure the Gantt chart depicts Task 1 then Task 2, followed by Tasks 3 and 4 overlapping during the same time interval.

Questions 8–10 · 45 marks

Question 8

15 marks

Customer database scanning, mail merge, and backup redundancy

Computational thinking, problem-solving and programming
System fundamentals

(a)

6 marks

Initialize variables and output lists:
Set CURR_DATE to current date. Create empty lists LIST1, LIST2, LIST3.
Iterate across customer records:
Loop through each CUST record in CUSTOMER_DATABASE.
Compute date difference:
Compute DUE_PERIOD = CURR_DATE - CUST.PAYMENT_DATE.
Categorize by payment status:
1. If payment is due in the next 30 days (DUE_PERIOD >= -30 and DUE_PERIOD <= 0): add CUST to LIST1.
2. If payment is overdue between 15 and 30 days (DUE_PERIOD > 14 and DUE_PERIOD <= 30): add CUST to LIST2.
3. If payment is overdue by more than 30 days (DUE_PERIOD > 30): add CUST to LIST3 and set CUST.FLAGGED_FOR_DELETION = true.
End loop.

Mentor tip

Ensure strict inequality boundaries (> 14 and <= 30 vs > 30) and flag for deletion rather than executing direct record deletion.

(b)

4 marks

Explain mail merge automated pipeline:
1. Standard document templates are prepared in the word processor with static wording and dynamic placeholders (e.g., <<Customer_Name>>, <<Due_Date>>, <<Amount>>).
2. The compiled lists provide customer IDs to query records from the customer database.
3. The word processor merges the fetched fields into the corresponding template placeholders to generate individualized notification letters.
4. The generated documents are automatically queued to a printer for postal mailing or dispatched via an email server gateway.

Mentor tip

Describe template placeholders, linking customer IDs to records, substituting personal details, and automated dispatch.

(c)

2 marks

Consequence to customers:
Customers do not receive payment notices and may fail to pay on time, leading to unintentional cancellation of their insurance policies.
Consequence to company:
The business suffers uncollected revenue, customer churn, and severe reputational damage or regulatory penalties.

Mentor tip

State one customer outcome (uninsured risk exposure) and one company outcome (lost revenue and damaged reputation).

(d)

3 marks

Identify data loss prevention method:
Automated offsite / cloud backup system (or mirrored database server).
Describe operational details:
Regular automated incremental snapshots and full backups are scheduled outside business hours and stored securely at an offsite location. If data corruption or hardware failure occurs, customer records can be restored from the most recent valid snapshot.

Mentor tip

Specify automated periodic snapshots transferred to an offsite secure location to facilitate restoration.

Question 9

15 marks

Network architectures, wireless trade-offs, and priority print scheduling

Networks
Computational thinking, problem-solving and programming

(a)

3 marks

Define the OSI model:
The Open Systems Interconnection (OSI) model is a theoretical 7-layer framework establishing global standards for computer network communication.
Explain layer abstraction:
Communication tasks are partitioned across 7 modular layers, where each layer provides dedicated services to the layer above and communicates through standard interfaces.
Give a layer example:
For example, the Transport layer handles reliable end-to-end data transfer and flow control, while the Data Link layer frames raw bits and manages MAC addressing.

Mentor tip

State that it is a 7-layer standardized reference framework for networking, highlighting functional separation and naming an example layer.

(b)

3 marks

Define communication protocol:
A protocol is an agreed set of formal rules and data formats that govern how devices communicate across a network.
Explain purpose with an example:
Protocols ensure reliable coordination and error-free communication across diverse operating platforms. For example, TCP handles packet sequencing and retransmission of lost packets to maintain data integrity.

Mentor tip

Provide a clear definition (rules governing transmission) and cite a network-specific protocol like TCP/IP.

(c)

4 marks

Advantage of wireless access:
Enhanced mobility: Staff can carry laptops and mobile devices to meeting rooms or throughout the office while maintaining continuous access to the server without physical network cables.
Disadvantage of wireless access:
Security vulnerabilities and signal interference: Radio signals extend outside the office building walls, exposing the network to unauthorized eavesdropping or packet sniffing unless robust encryption (e.g., WPA3) is strictly enforced.

Mentor tip

Pair one mobility benefit with one security or signal interference drawback, providing an explanation for each.

(d)

5 marks

Step 1 - Starvation check (waiting time threshold):
Iterate through the entire collection of print jobs. If any job has a waiting time greater than 10 minutes (CURRENT_TIME - job.TIME_SENT > 10), immediately select and return that job for printing.
Step 2 - Priority level scanning:
If no job has exceeded 10 minutes, search the collection by priority levels from highest (priority 1) to lowest (priority 4):
For priority LEVEL = 1 to 4:
Iterate through all jobs in the collection in chronological submission order.
If a job matches the current priority LEVEL, return it immediately to be printed next.
Step 3 - Complete search upon first match:
Exit the routine as soon as the highest-priority eligible print job is returned.

Mentor tip

Check the 10-minute timeout condition first across all jobs, then search in ascending order of priority level from 1 to 4.

Question 10

15 marks

Comparison of sorting algorithms and object encapsulation

Computational thinking, problem-solving and programming

(a)

4 marks

Two similarities between bubble sort and selection sort:
1. Both employ nested loops to iterate through the array, reducing the unsorted partition boundary on each outer pass.
2. Both operate in-place with $O (1)$ auxiliary memory overhead.
Two differences between bubble sort and selection sort:
1. Bubble sort compares and swaps adjacent elements repeatedly during a pass, whereas selection sort searches for the extremum across the unsorted slice and performs at most one swap per outer pass.
2. Bubble sort can detect an already-sorted array and terminate early in $O (n)$ time using a boolean flag, whereas standard selection sort always performs $O (n^{2})$ comparisons regardless of initial array order.

Mentor tip

State 2 clear similarities (nested loops, in-place) and 2 clear differences (adjacent swapping vs single swap per pass; early exit capability).

(b)

2 marks

Explain efficiency advantage for top 10 extraction:
1. Selection sort can be configured to execute only 10 outer passes to extract the 10 fastest times into the first 10 positions.
2. Bubble sort cannot isolate the 10 fastest times at the beginning without performing complete bubble passes across the entire 150-element array, requiring significantly more swap operations.

Mentor tip

Explain that selection sort only needs 10 outer iterations to find the 10 fastest times, saving massive unnecessary operations.

(c)

6 marks

Initialize tracking variables:
Set TRANSFER = 0.
Outer loop for top 10 elements:
Loop while TRANSFER < 10:
Set MIN_VAL = TIMES[TRANSFER] and MIN_INDEX = TRANSFER.
Inner loop across remaining unsorted competitors (COUNT from TRANSFER + 1 to 149):
If TIMES[COUNT] < MIN_VAL then:
MIN_VAL = TIMES[COUNT]
MIN_INDEX = COUNT
End if
End inner loop.
Copy minimum to fastest array: FASTEST[TRANSFER] = TIMES[MIN_INDEX].
Swap elements in TIMES to preserve remaining items: swap TIMES[TRANSFER] and TIMES[MIN_INDEX].
Increment TRANSFER = TRANSFER + 1.
End outer loop.

Mentor tip

Run the outer selection loop exactly 10 times, selecting the minimum time each pass and storing it into FASTEST.

(d)

3 marks

Limitations of parallel arrays:
Parallel arrays (TIMES[] and NAMES[]) store attributes separately, requiring synchronized dual-index updates during sorting or swapping. Any uncoordinated update corrupts the linkage between competitor names and times.
Advantages of unified objects:
An array of Competitor objects bundles name and time attributes into a single cohesive entity. Sorting only requires moving object references within a single array, eliminating synchronization errors and improving code maintainability.

Mentor tip

Explain that parallel arrays risk index desynchronization during swaps, whereas objects encapsulate related fields so a single swap maintains full data integrity.

Our analysis

Where the marks are

Each part sorted by the topic it mostly tests. Computational thinking, problem-solving and programming carries the most marks on this paper.

Computational thinking, problem-solving and programming32 marks · 46%
Q3, Q4, Q8, Q9, Q10
System fundamentals21 marks · 30%
Q5, Q6, Q7, Q8
Networks13 marks · 19%
Q2, Q9
Computer organisation4 marks · 6%
Q1

Mentor insights

Traps to watch for

01
Truth table evaluation order for compound clauses · Q1
Remember to evaluate not C before applying the OR with B. When B is 1, (not C or B) is always 1 regardless of C.
02
Task dependency and concurrency in Gantt scheduling · Q7
Report writing and presentation preparation can only begin after water sample collection and laboratory analysis are fully completed, but can run concurrently alongside each other.
03
Print queue priority starvation check precedence · Q9
The 10-minute waiting time starvation threshold overrides all job priority classes; any job waiting longer than 10 minutes must be printed next before scanning priority levels 1 through 4.
04
Selection sort efficiency when extracting partial rankings · Q10
Selection sort can isolate the 10 fastest competitors by executing only 10 outer loop passes, whereas bubble sort must traverse the entire 150-element array repeatedly.

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: May 2015
Marks: 70
Duration: 1 hour 30 min
Calculator: Not allowed
Questions: 10

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10

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

Practice mode

Hide our working until you've had a go.

Questions 1–7 · 25 marks

Question 1

4 marks

Truth table for compound Boolean expression

Computer organisation

(a)

4 marks

Analyze the Boolean expression:
Expression: $(A \lor B) \land (\neg C \lor B)$ .
Evaluate intermediate terms for all 8 combinations of inputs $(A, B, C)$ :
1. For $A = 0, B = 0, C = 0$ : $A \lor B = 0$ , $\neg C \lor B = 1 \lor 0 = 1$ . Final output: $0 \land 1 = 0$ .
2. For $A = 0, B = 0, C = 1$ : $A \lor B = 0$ , $\neg C \lor B = 0 \lor 0 = 0$ . Final output: $0 \land 0 = 0$ .
3. For $A = 0, B = 1, C = 0$ : $A \lor B = 1$ , $\neg C \lor B = 1 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .
4. For $A = 0, B = 1, C = 1$ : $A \lor B = 1$ , $\neg C \lor B = 0 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .
5. For $A = 1, B = 0, C = 0$ : $A \lor B = 1$ , $\neg C \lor B = 1 \lor 0 = 1$ . Final output: $1 \land 1 = 1$ .
6. For $A = 1, B = 0, C = 1$ : $A \lor B = 1$ , $\neg C \lor B = 0 \lor 0 = 0$ . Final output: $1 \land 0 = 0$ .
7. For $A = 1, B = 1, C = 0$ : $A \lor B = 1$ , $\neg C \lor B = 1 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .
8. For $A = 1, B = 1, C = 1$ : $A \lor B = 1$ , $\neg C \lor B = 0 \lor 1 = 1$ . Final output: $1 \land 1 = 1$ .

A 00001111 B 00110011 C 01010101 A \lor B 00111111 \neg C \lor B 10111011 (A \lor B) \land (\neg C \lor B) 00111011

Mentor tip

Recognize that whenever input B is 1, both OR clauses evaluate to 1, guaranteeing an output of 1 regardless of A or C.

Question 2

3 marks

Application and function of a virtual private network

Networks

(a)

3 marks

Outline a practical VPN scenario:
A remote employee working from home or travelling needs to connect securely to the organization's private corporate network.
Explain technical implementation:
1. The remote computer initiates an encrypted virtual tunnel over the unsecure public internet to the organization's VPN server.
2. The VPN encapsulates all transmitted packets with IPsec or SSL/TLS encryption, preventing unauthorized interception while allowing seamless access to restricted internal resources.

Mentor tip

State a valid use case (remote worker access) and elaborate on the creation of an encrypted communication tunnel over public infrastructure.

Question 3

2 marks

Sub-procedures as programmatic abstraction

Computational thinking, problem-solving and programming

(a)

2 marks

Define procedural abstraction:
A sub-procedure encapsulates a specific sub-task within a named block of code, exposing only a clear parameter interface while concealing its internal operational implementation details.
Explain how it functions as abstraction:
Callers invoke the sub-procedure by its identifier without needing to know or manage the low-level logic, loops, or internal variables executing inside it, thereby reducing mental complexity.

Mentor tip

Focus on hiding implementation complexity behind a reusable callable interface.

Question 4

4 marks

Algorithm tracing for perfect number verification

Computational thinking, problem-solving and programming

(a)

4 marks

Analyze algorithmic parameters:
Input: $N = 6, SUM = 0$ . The loop increments $COUNT$ from $1$ to $(N div 2) = 3$ .
Trace each iteration:
Iteration 1 (COUNT = 1): $6 mod 1 = 0$ (True). $SUM = 0 + 1 = 1$ .
Iteration 2 (COUNT = 2): $6 mod 2 = 0$ (True). $SUM = 1 + 2 = 3$ .
Iteration 3 (COUNT = 3): $6 mod 3 = 0$ (True). $SUM = 3 + 3 = 6$ .
Evaluate loop termination and output check:
Loop finishes as $COUNT$ completes value 3.
Condition check: $SUM = N ⟹ 6 = 6$ (True).
Output: "perfect".

COUNT 123 N (mod COUNT) = 0 True True True SUM 01366 SUM = N True Output "perfect"

Mentor tip

Record values after each loop step clearly in the trace table columns.

Question 5

4 marks

Hardware usability features of modern laptops

System fundamentals

(a)

4 marks

Feature 1 - High-resolution anti-glare display with scaling controls:
Usability impact: Provides clear visual contrast and adjustable font sizes, minimizing eyestrain and assisting users with visual impairments in diverse lighting conditions.
Feature 2 - Multi-touch touchpad with adjustable sensitivity and tactile feedback:
Usability impact: Enables precise cursor manipulation and customizable gestures (pinch-to-zoom, two-finger scrolling), accommodating users with motor skill variations or repetitive strain.

Mentor tip

Identify two distinct hardware usability characteristics and clearly explain how each accommodates varying user capabilities or ergonomics.

Question 6

2 marks

Software update notification mechanisms

System fundamentals

(a)

2 marks

Describe automatic update polling:
The client application contains a background service that queries the developer's update repository on application startup or via a scheduled timer.
Explain user notification delivery:
If a newer version hash is discovered, the program presents an in-app banner or pop-up notification prompting the user to install the patch immediately or view release notes.

Mentor tip

Outline both the detection method (startup query to update server) and presentation to the user (in-app pop-up or notification banner).

Question 7

6 marks

Project task sequencing, concurrency, and Gantt scheduling

System fundamentals

(a)

2 marks

Identify 4 sequential project phases:
1. Collect water samples from the four lakes.
2. Laboratory analysis of the water samples.
3. Write the scientific report.
4. Prepare the animated computer presentation.

Mentor tip

List the four tasks in logical chronological sequence from data collection to report and presentation preparation.

(b)

2 marks

Identify concurrent tasks:
"Write the scientific report" and "Prepare the animated computer presentation".
Explain concurrency mechanism:
Once the laboratory sample data is finalized, the 6 students can split into sub-teams: one group drafts the textual report while the other builds the animated slides simultaneously using the same shared dataset.

Mentor tip

Writing the report and creating the presentation can occur concurrently since different group members work simultaneously on shared analysis findings.

(c)

2 marks

Construct Gantt chart schedule representation:
Show sequential dependencies followed by parallel execution across phases:
Phase 1: Task 1 (Collect water samples).
Phase 2: Task 2 (Analyse water samples) begins only after Phase 1 finishes.
Phase 3: Task 3 (Write scientific report) and Task 4 (Prepare animated presentation) run concurrently in parallel.

Task 1. Collect samples 2. Analyse samples 3. Write report 4. Prepare presentation Phase 1 [■] Phase 2 [■] Phase 3 [■] [■]

Mentor tip

Ensure the Gantt chart depicts Task 1 then Task 2, followed by Tasks 3 and 4 overlapping during the same time interval.

Questions 8–10 · 45 marks

Question 8

15 marks

Customer database scanning, mail merge, and backup redundancy

Computational thinking, problem-solving and programming
System fundamentals

(a)

6 marks

Initialize variables and output lists:
Set CURR_DATE to current date. Create empty lists LIST1, LIST2, LIST3.
Iterate across customer records:
Loop through each CUST record in CUSTOMER_DATABASE.
Compute date difference:
Compute DUE_PERIOD = CURR_DATE - CUST.PAYMENT_DATE.
Categorize by payment status:
1. If payment is due in the next 30 days (DUE_PERIOD >= -30 and DUE_PERIOD <= 0): add CUST to LIST1.
2. If payment is overdue between 15 and 30 days (DUE_PERIOD > 14 and DUE_PERIOD <= 30): add CUST to LIST2.
3. If payment is overdue by more than 30 days (DUE_PERIOD > 30): add CUST to LIST3 and set CUST.FLAGGED_FOR_DELETION = true.
End loop.

Mentor tip

Ensure strict inequality boundaries (> 14 and <= 30 vs > 30) and flag for deletion rather than executing direct record deletion.

(b)

4 marks

Explain mail merge automated pipeline:
1. Standard document templates are prepared in the word processor with static wording and dynamic placeholders (e.g., <<Customer_Name>>, <<Due_Date>>, <<Amount>>).
2. The compiled lists provide customer IDs to query records from the customer database.
3. The word processor merges the fetched fields into the corresponding template placeholders to generate individualized notification letters.
4. The generated documents are automatically queued to a printer for postal mailing or dispatched via an email server gateway.

Mentor tip

Describe template placeholders, linking customer IDs to records, substituting personal details, and automated dispatch.

(c)

2 marks

Consequence to customers:
Customers do not receive payment notices and may fail to pay on time, leading to unintentional cancellation of their insurance policies.
Consequence to company:
The business suffers uncollected revenue, customer churn, and severe reputational damage or regulatory penalties.

Mentor tip

State one customer outcome (uninsured risk exposure) and one company outcome (lost revenue and damaged reputation).

(d)

3 marks

Identify data loss prevention method:
Automated offsite / cloud backup system (or mirrored database server).
Describe operational details:
Regular automated incremental snapshots and full backups are scheduled outside business hours and stored securely at an offsite location. If data corruption or hardware failure occurs, customer records can be restored from the most recent valid snapshot.

Mentor tip

Specify automated periodic snapshots transferred to an offsite secure location to facilitate restoration.

Question 9

15 marks

Network architectures, wireless trade-offs, and priority print scheduling

Networks
Computational thinking, problem-solving and programming

(a)

3 marks

Define the OSI model:
The Open Systems Interconnection (OSI) model is a theoretical 7-layer framework establishing global standards for computer network communication.
Explain layer abstraction:
Communication tasks are partitioned across 7 modular layers, where each layer provides dedicated services to the layer above and communicates through standard interfaces.
Give a layer example:
For example, the Transport layer handles reliable end-to-end data transfer and flow control, while the Data Link layer frames raw bits and manages MAC addressing.

Mentor tip

State that it is a 7-layer standardized reference framework for networking, highlighting functional separation and naming an example layer.

(b)

3 marks

Define communication protocol:
A protocol is an agreed set of formal rules and data formats that govern how devices communicate across a network.
Explain purpose with an example:
Protocols ensure reliable coordination and error-free communication across diverse operating platforms. For example, TCP handles packet sequencing and retransmission of lost packets to maintain data integrity.

Mentor tip

Provide a clear definition (rules governing transmission) and cite a network-specific protocol like TCP/IP.

(c)

4 marks

Advantage of wireless access:
Enhanced mobility: Staff can carry laptops and mobile devices to meeting rooms or throughout the office while maintaining continuous access to the server without physical network cables.
Disadvantage of wireless access:
Security vulnerabilities and signal interference: Radio signals extend outside the office building walls, exposing the network to unauthorized eavesdropping or packet sniffing unless robust encryption (e.g., WPA3) is strictly enforced.

Mentor tip

Pair one mobility benefit with one security or signal interference drawback, providing an explanation for each.

(d)

5 marks

Step 1 - Starvation check (waiting time threshold):
Iterate through the entire collection of print jobs. If any job has a waiting time greater than 10 minutes (CURRENT_TIME - job.TIME_SENT > 10), immediately select and return that job for printing.
Step 2 - Priority level scanning:
If no job has exceeded 10 minutes, search the collection by priority levels from highest (priority 1) to lowest (priority 4):
For priority LEVEL = 1 to 4:
Iterate through all jobs in the collection in chronological submission order.
If a job matches the current priority LEVEL, return it immediately to be printed next.
Step 3 - Complete search upon first match:
Exit the routine as soon as the highest-priority eligible print job is returned.

Mentor tip

Check the 10-minute timeout condition first across all jobs, then search in ascending order of priority level from 1 to 4.

Question 10

15 marks

Comparison of sorting algorithms and object encapsulation

Computational thinking, problem-solving and programming

(a)

4 marks

Two similarities between bubble sort and selection sort:
1. Both employ nested loops to iterate through the array, reducing the unsorted partition boundary on each outer pass.
2. Both operate in-place with $O (1)$ auxiliary memory overhead.
Two differences between bubble sort and selection sort:
1. Bubble sort compares and swaps adjacent elements repeatedly during a pass, whereas selection sort searches for the extremum across the unsorted slice and performs at most one swap per outer pass.
2. Bubble sort can detect an already-sorted array and terminate early in $O (n)$ time using a boolean flag, whereas standard selection sort always performs $O (n^{2})$ comparisons regardless of initial array order.

Mentor tip

State 2 clear similarities (nested loops, in-place) and 2 clear differences (adjacent swapping vs single swap per pass; early exit capability).

(b)

2 marks

Explain efficiency advantage for top 10 extraction:
1. Selection sort can be configured to execute only 10 outer passes to extract the 10 fastest times into the first 10 positions.
2. Bubble sort cannot isolate the 10 fastest times at the beginning without performing complete bubble passes across the entire 150-element array, requiring significantly more swap operations.

Mentor tip

Explain that selection sort only needs 10 outer iterations to find the 10 fastest times, saving massive unnecessary operations.

(c)

6 marks

Initialize tracking variables:
Set TRANSFER = 0.
Outer loop for top 10 elements:
Loop while TRANSFER < 10:
Set MIN_VAL = TIMES[TRANSFER] and MIN_INDEX = TRANSFER.
Inner loop across remaining unsorted competitors (COUNT from TRANSFER + 1 to 149):
If TIMES[COUNT] < MIN_VAL then:
MIN_VAL = TIMES[COUNT]
MIN_INDEX = COUNT
End if
End inner loop.
Copy minimum to fastest array: FASTEST[TRANSFER] = TIMES[MIN_INDEX].
Swap elements in TIMES to preserve remaining items: swap TIMES[TRANSFER] and TIMES[MIN_INDEX].
Increment TRANSFER = TRANSFER + 1.
End outer loop.

Mentor tip

Run the outer selection loop exactly 10 times, selecting the minimum time each pass and storing it into FASTEST.

(d)

3 marks

Limitations of parallel arrays:
Parallel arrays (TIMES[] and NAMES[]) store attributes separately, requiring synchronized dual-index updates during sorting or swapping. Any uncoordinated update corrupts the linkage between competitor names and times.
Advantages of unified objects:
An array of Competitor objects bundles name and time attributes into a single cohesive entity. Sorting only requires moving object references within a single array, eliminating synchronization errors and improving code maintainability.

Mentor tip

Explain that parallel arrays risk index desynchronization during swaps, whereas objects encapsulate related fields so a single swap maintains full data integrity.

Our analysis

Where the marks are

Each part sorted by the topic it mostly tests. Computational thinking, problem-solving and programming carries the most marks on this paper.

Computational thinking, problem-solving and programming32 marks · 46%
Q3, Q4, Q8, Q9, Q10
System fundamentals21 marks · 30%
Q5, Q6, Q7, Q8
Networks13 marks · 19%
Q2, Q9
Computer organisation4 marks · 6%
Q1

Mentor insights

Traps to watch for

01
Truth table evaluation order for compound clauses · Q1
Remember to evaluate not C before applying the OR with B. When B is 1, (not C or B) is always 1 regardless of C.
02
Task dependency and concurrency in Gantt scheduling · Q7
Report writing and presentation preparation can only begin after water sample collection and laboratory analysis are fully completed, but can run concurrently alongside each other.
03
Print queue priority starvation check precedence · Q9
The 10-minute waiting time starvation threshold overrides all job priority classes; any job waiting longer than 10 minutes must be printed next before scanning priority levels 1 through 4.
04
Selection sort efficiency when extracting partial rankings · Q10
Selection sort can isolate the 10 fastest competitors by executing only 10 outer loop passes, whereas bubble sort must traverse the entire 150-element array repeatedly.

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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