SL · 75 minutes · 50 marks
Instructions
Answer every question in Section A and Section B.
The marks for each question are shown in square brackets, such as [3].
Answer on paper or on screen. Each question links to its own page, where you can type an answer and mark it against its marking points.
Times and marks follow public descriptions of the new course, which Spine has not yet checked against the IB's subject guide. Your school's mocks may differ.
Answer all questions.
A school's lighting controller stores each room's brightness level as one unsigned byte.
(a) Convert the denary value 183 into 8-bit binary. [1]
(b) Convert the denary value 183 into hexadecimal. [1]
(c) Another room's level is stored as hexadecimal 3E. Convert 3E into denary. [1]
Show your working.
[3]
A wildlife camera in a nature reserve saves uncompressed bitmap photos that are 1024 pixels wide and 768 pixels high, with a colour depth of 24 bits.
(a) Calculate the size of one photo in bytes. Ignore any file header. [2]
(b) To save space, the colour depth is reduced to 16 bits. State how many different colours each pixel can then show. [1]
[3]
A bike-share docking station stands outside all year. Its small computer stores the station's software and a log of hires, which is a few gigabytes in total.
Explain why a solid-state drive (SSD) is a better choice than a hard disk drive (HDD) for this computer. [3]
A student's laptop has three processes ready to run at time 0, in the order shown. Each needs the CPU for the number of time units in the table.
| Process | CPU time needed |
|---|---|
| P1 (video export) | 5 |
| P2 (chat message) | 2 |
| P3 (spell check) | 3 |
(a) Deduce the time at which each process finishes under first come first served (FCFS) scheduling. [1]
(b) Deduce the time at which each process finishes under round robin scheduling with a time slice of 2 units. A process that has not finished goes to the back of the queue. Show the order in which the processes use the CPU. [2]
(c) Explain why round robin suits the chat program better than FCFS does. [2]
[5]
A school has 400 devices that use private IP addresses, but the school has only one public IP address.
(a) Distinguish between an IP address and a MAC address. [2]
(b) State the technique the school router uses to let all 400 devices reach the internet through the one public IP address. [1]
[3]
A school has four buildings, and each building has its own switch. The school is choosing how to cable the four building switches together. Option 1 is a star: a new core switch in the server room, with one cable to each building switch. Option 2 is a full mesh: a cable directly between every pair of building switches.
(a) Calculate the number of cables Option 2 needs. [1]
(b) Compare Option 1 and Option 2 in terms of cost and resilience. [2]
[3]
A student at home uploads a large photo of a science poster to the school's file server. The photo is sent across the internet using packet switching.
(a) State one item, other than part of the photo itself, that each packet carries. [1]
(b) Explain why the packets can arrive at the file server in a different order from the one they were sent in. [2]
[3]
A school has a firewall between its router and the internet. One morning a student plugs in a USB stick at a library computer, and malware on the stick spreads to other computers on the school network.
(a) Outline what the firewall does. [2]
(b) Explain why the firewall did not stop the malware from spreading. [2]
[4]
A school drama club stores all its data in one table, Casting.
| student_id | student_name | role | play_title | play_date |
|---|---|---|---|---|
| 11 | Priya | Narrator | The Lighthouse | 2026-12-04 |
| 12 | Tom | Keeper | The Lighthouse | 2026-12-04 |
| 13 | Ines | Fox | Winter Market | 2027-03-12 |
| 11 | Priya | Baker | Winter Market | 2027-03-12 |
| 14 | Omar | Captain | Paper Boats | 2027-05-20 |
(a) The Winter Market performance moves to 2027-03-19. Describe the update anomaly that can happen with this table. [2]
(b) Omar leaves the club and his record is deleted. Describe the deletion anomaly: what else the database loses, apart from Omar's own details. [1]
[3]
A music school has drawn an entity relationship design for its lessons. These tables describe it.
| Entity | Attributes |
|---|---|
| Student | student_id (primary key), name |
| Course | course_code (primary key), instrument, grade_level |
| Teacher | teacher_id (primary key), name |
| Relationship | Cardinality |
|---|---|
| Teacher teaches Course | one-to-many (each course has exactly one teacher) |
| Student enrols on Course | many-to-many |
(a) Explain why the relationship between Student and Course cannot be put into tables by adding one foreign key to Student or to Course. [1]
(b) Construct a set of tables that puts this whole design into a relational database. For each table, give its attributes, its primary key and any foreign keys. [3]
[4]
A school trains a model to flag students who may need extra reading support. The labels in the training data record which students teachers referred for support over the last ten years. In those years, teachers referred boys much more often than girls who had similar reading scores. On the records from those ten years, the model agrees with the teachers' decisions 92% of the time.
(a) Explain how bias has entered this model. [2]
(b) Explain why the 92% accuracy does not show that the model is fair. [2]
[4]
Section B is in the case-study format, on a practice scenario written by Spine. It is not the IB's case study for your exam year. Read the scenario first. Each question refers to it.
Practice scenario (written by Spine, not an IB case study):
Larkford is a small city with a community bike-share called LarkBikes. It has 40 docking stations, each with between 10 and 20 docks. Each dock has a sensor that detects whether a bike is locked in it and reads the bike's ID tag. Every station sends its sensor readings to a central server over the mobile phone network every 5 minutes.
Riders register in the LarkBikes app with their name, email address, home postcode and date of birth. When a rider unlocks a bike, a trip starts. The server keeps riders, bikes, stations and trips in a relational database. Each trip record holds the rider, the bike, the start station, the end station, and the start and end times. The database now holds two years of trips.
Every evening, a machine learning model is trained on the trip records together with the hour of the day, the day of the week, whether it is a school holiday, and the weather. For each station, it predicts how many bikes will be taken in each hour of the next day. A van crew uses these predictions to move bikes to stations that are expected to run out.
The 28 stations in the city centre are busy. The 12 stations in the outer districts were added last year and record far fewer trips.
The manager of LarkBikes suggests a change. The model would also take, as a feature, each station's current number of bikes from the latest sensor readings. It would still be retrained once each evening, on the past trips and the stored sensor readings. During the day, the trained model would be run again every 5 minutes on the newest readings, to update the predictions for the rest of the day. All of this would run on the existing central server.
Evaluate this suggestion. [4]
(a) State whether the LarkBikes model performs classification or regression, and give a reason. [2]
(b) Identify one feature the model uses and the label it learns to predict. [2]
[4]
The model predicts few trips at the outer-district stations, so the van rarely brings bikes there. Riders in the outer districts often find those stations empty.
Discuss whether it is fair to use the model's predictions to decide where the van takes bikes. [4]