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Past Paper Practice

Computer Systems  ·  Lesson 10 of 10 Approx 60 min Revision and exam technique
Learning intentions
  • Practise the Computer Systems topics that appear regularly in National 5 question papers.
  • Use SQA command words such as state, identify, describe, explain and calculate accurately.
  • Improve written answers by matching each mark to a clear, specific point.
Success criteria
  • I can answer quick Computer Systems recall questions without over-writing.
  • I can show working for binary and storage calculations so my method is clear.
  • I can write context-based descriptions and explanations that would earn marks in a marking instruction.
Warm up — short-response speed check

These are the kind of quick Computer Systems marks pupils should bank confidently before moving on to harder context questions.

1. What is the 8-bit binary representation of the denary number 79?

2. A seven-character name is stored using extended ASCII. How many bits are required?

3. Which answer best describes what encryption does?

Key vocabulary

command word
The instruction in a question, such as state, identify, describe, explain or calculate.
mark allocation
The number of marks available. It usually tells you how many separate points are needed.
context
The real-world situation in the question. Strong answers connect the computing idea to that situation.
positive marking
Marks are awarded for correct, relevant points rather than removed for every small mistake.
working
The calculation steps that show how an answer was reached, especially for binary and storage questions.
technical language
Precise Computing Science terms such as ALU, register, firewall, encryption, bitmap or mantissa.
restricted response
A short answer question where only one or two precise points are needed.
extended response
A longer answer where a description, explanation or comparison must be developed across several marks.

How to Approach Computer Systems Past Paper Questions

What the paper expects

Computer Systems appears in Section 1 alongside Software Design and Development. It is not optional, so every pupil has to collect these marks. The official course specification gives Computer Systems a range of 10 to 14 marks in the question paper. That means the topic is smaller than programming, databases or web, but it matters because the questions are usually clear, short and very markable. A well-prepared pupil should aim to pick up most of these marks.

The pattern in recent papers

Recent papers have sampled across data representation, computer structure, translators, energy use and security. Typical questions ask for an 8-bit binary conversion, a text storage calculation using 8-bit extended ASCII, the mantissa and exponent from a floating-point number, the graphic representation used for a photograph, a processor component such as the ALU or registers, a reason for standby mode, or the security method that stops intercepted data being read. These questions often look simple, but they still require exact wording.

Command words are the steering wheel

For state or identify, give the answer and stop. If the question asks for the part of the processor that performs calculations, write ALU; do not write a paragraph about the whole processor. For calculate, show enough working to make the arithmetic visible. For describe, give a developed point about what happens or why it is used. For explain, include a reason, usually linked to the context. The 2025 course report highlights that pupils often find describe and explain questions more demanding because answers are vague or not connected to the situation.

Use the marks as a checklist

A 1-mark Computer Systems question normally needs one accurate point. A 2-mark question usually needs two separate points, or one answer plus a linked explanation. A 3-mark answer should be planned as three markable statements. Avoid giving extra guesses after a correct answer. If a question asks for two items and a pupil gives three, an incorrect extra item can spoil the response. It is better to be precise than to empty your brain onto the page.

Show calculations clearly

Binary and storage questions are some of the most reliable marks if the method is practised. For binary, write the place values 128 64 32 16 8 4 2 1, then select the values that add to the denary number. For text storage, remember that extended ASCII uses 8 bits per character, including spaces and punctuation. If a question asks for bits, stop at bits. If it asks for bytes, divide by 8. If it asks for kilobytes and the course context uses binary units, use 1024 bytes per kilobyte.

Answer in context

For energy and security questions, a generic answer may be too weak. If a question says a phone is tracking a journey, "switch it off" may not fit because the phone still needs to track. A better answer might be to dim the screen, turn off unused features or use low-power mode. If a question says an email may be intercepted, encryption is the answer because it makes the content unreadable without the key. If a question asks about a firewall, describe how it monitors traffic and blocks unauthorised access.

Worked examples

Example 1 — Binary conversion

Question: Convert the denary number 156 to an 8-bit binary number.

1
Write the place values: 128 64 32 16 8 4 2 1.
2
Build 156: 128 + 16 + 8 + 4 = 156. The selected columns are 128, 16, 8 and 4.
3
Put 1s in selected columns and 0s elsewhere: 10011100.
Example 2 — Text storage

Question: Calculate the number of bits required to store the text East End! using extended ASCII.

1
Count every character, including the space and punctuation: E a s t space E n d ! = 9 characters.
2
Extended ASCII uses 8 bits for each character.
3
Calculate 9 × 8 = 72 bits. The final answer is 72 bits.
Example 3 — Context-based explanation

Question: A school tablet sends assessment data over a wireless network. Explain why the data should be encrypted.

1
Identify the security risk in the context: data is being transmitted and could be intercepted.
2
State what encryption does: it scrambles the data so it cannot be understood without the key.
3
Link both together: if the assessment data is intercepted, encryption prevents others from reading the pupils' results.
Now you try

A fitness app stores a user's weekly step total as binary, sends a summary email, and uses standby mode when the phone has not been touched for a few minutes.

Answer the following:

  1. Convert the denary number 143 to 8-bit binary.
  2. State what can be done so the summary email cannot be read if intercepted.
  3. Describe why standby mode is suitable when the phone is not being used for a few minutes.
  1. 10001111, because 128 + 8 + 4 + 2 + 1 = 143.
  2. Use encryption so the email content is scrambled and cannot be understood without the correct key.
  3. Standby mode reduces energy use while allowing the phone to wake quickly when the user returns.
Common mistakes
✕
Ignoring the command word. A state question does not need a paragraph, while an explain question needs a reason linked to the context.
✕
Forgetting spaces in text storage. Spaces, digits and punctuation are characters too. Each one uses 8 bits in extended ASCII.
✕
Mixing up firewall and encryption. A firewall blocks unauthorised network traffic. Encryption protects the meaning of data if it is intercepted.
✕
Giving extra guesses. If a question asks for one answer, give one answer. Extra wrong answers can cancel out otherwise correct work.
Exam tip

For Computer Systems, read the mark allocation before writing. One mark usually means one crisp technical point. Two marks usually means two crisp points or a point plus a reason. If the question includes a scenario, use words from that scenario in your answer. That is the easiest way to turn a memorised fact into an applied answer.

Task Set

Questions 1-5 are auto-checked. Questions 6-9 are self-marked using SQA-style marking points.

1. Convert the denary number 174 to an 8-bit binary number. TYPE 1

2. Identify the mantissa and exponent in 0.643 × 105. TYPE 1

3. A photograph is stored as an array of pixels. Which graphic representation is being used? TYPE 1

4. Which processor component performs arithmetic and logical operations? TYPE 1

5. Which statement about a compiler is correct? TYPE 1

6. A music club stores the member name Jazz Lab using extended ASCII. Calculate the number of bits required. Show your working. TYPE 2

Marking points: 8 characters including the space. Extended ASCII uses 8 bits per character. 8 × 8 = 64 bits. Award the mark for the correct final answer with working.

7. A school laptop is left unused during lunch. Describe one reason why using standby mode is better than leaving it fully powered on. TYPE 2

Model answer: Standby mode reduces the energy used while the laptop is not being used, which lowers electricity use and environmental impact. It can also wake more quickly than a full shutdown.

8. A home router uses a firewall. Describe how the firewall helps protect the home network. TYPE 3

Model answer: A firewall monitors network traffic entering and leaving the network. It blocks unauthorised or suspicious traffic, helping prevent attackers from accessing devices on the home network.

9. A pupil writes: "Encryption stops hackers getting into a network." Improve this answer for a question about an intercepted message. TYPE 3

Model answer: Encryption scrambles the message so it cannot be understood if it is intercepted. Only someone with the correct decryption key can read the original message. The answer should not describe blocking access; that is the role of a firewall.
Teacher notes — Shift+T to hide

Suggested timing: 60 minutes. Warm up 8 min; notes and discussion 15 min; worked examples 12 min; now you try 8 min; task set 17 min.

Official reference point: Built from the current SQA/Qualifications Scotland course specification, recent N5 question papers and marking instructions, the 2025 course report, and Understanding Standards guidance. Questions here are original SQA-style practice, not copied wholesale from a live paper.

Key misconception to address: Pupils often know the fact but lose the mark because they do not link it to the context, especially for describe/explain security and energy questions.

Live demo suggestion: Put a 2-mark answer on the board and ask pupils to highlight each separate markable point in a different colour.

Extension question: Write a 10-mark mini Computer Systems section containing five 1-mark questions, one 2-mark question and one 3-mark question, then swap with a partner to mark.

SQA command words covered: state, identify, calculate, describe, explain, improve.