I can show what I know across all four areas of the Computer Systems unit under test conditions.
I can use my marked answers to find the topics I need to revise before the prelim.
Success criteria
I can carry out two's complement and floating-point conversions accurately, showing every step.
I can answer "describe" and "explain" questions with one clear point per mark.
I can list at least two topics to revise, with evidence from my own test.
Warm up — know the test before you start
Read the "How this test works" section below, then answer these three questions.
WU1
1. How many marks is this test out of?
WU2
2. Which area of the Computer Systems unit does the Computer Misuse Act belong to?
WU3
3. A "describe" question is worth 3 marks. How many separate points should your answer make, at least?
Key vocabulary
State
Give a short answer — a fact, a value or a name. No explanation needed.
Describe
Give the features or steps of something, one point per mark.
Explain
Say how or why — link a cause to its effect ("…because…", "…so…").
Show your working
In conversions, write every step. A correct method can earn marks even if the final answer slips.
How this test works
What it covers
This test covers every content statement in the Computer Systems part of the Higher course specification. It has four areas, and the marks follow how much there is to learn in each one. Data representation is worth the most (16 marks) because it has the most content and the most calculation. Computer structure is worth 8 marks, environmental impact 3, and security risks and precautions 13. In the final exam, Computer Systems is only examined in Section 1, alongside Software Design and Development, so treat this test as practice for the exam as well as a unit check.
Area
Lessons
Questions
Marks
1.1 Data representation
CS1–CS5
Q1–Q12
16
1.2 Computer structure
CS6–CS8
Q13–Q16
8
1.3 Environmental impact
CS9
Q17
3
1.4 Security risks and precautions
CS10–CS12
Q18–Q24
13
Total
24 questions
40
How to sit it
Work on your own, with no notes, and try to finish in one lesson. Each question shows its marks. Use them to decide how much to write: a 1-mark "state" question needs a word or a number, and a 3-mark "describe" question needs three separate points. Leave nothing blank. A short attempt can still earn a mark, and a blank never does. Write all your answers first, and only press Check answers once you have finished the whole test. The test is only useful if your answers are really yours.
How it is marked
Questions with a number or a single word are checked automatically. For binary and floating-point answers you can include or leave out spaces between groups of bits. Written answers are self-marked: once you press Check, a model answer appears under each one. Compare your answer point by point and choose I got this, I missed something or I need to revisit. Be honest. The score is for you, and an inflated score hides exactly the gaps you need to find before the prelim. Your teacher may also mark the written answers using the same marking points.
After the test
Task Set C turns your results into a revision plan. Note every question you got wrong or only partly right, find its lesson in the coverage table, and revisit that lesson's worked examples before trying the question again. Conversions (Q2–Q8) are the questions most often lost to small slips. If you lost marks there, practise the method rather than rereading notes.
Worked examples — how marks are awarded
Example 1 — a 2-mark floating-point conversion
1
Question: represent 3.5 in normalised floating point with a 5-bit mantissa and a 3-bit exponent (both two's complement).
2
3.5 = 11.1₂. Normalise to 0.1… form by shifting the mantissa right 2 places (exponent +2): 0.1110 × 2². Mantissa = 01110.
3
Exponent = 2 → 3-bit two's complement 010. 1 mark for the mantissa, 1 mark for the exponent.
✓
01110 010. Check: 0.875 × 2² = 3.5 ✓
Example 2 — a 2-mark "explain" answer
1
Question: explain why increasing the clock speed can improve performance.
2
Point 1 (what changes): more clock cycles happen each second.
3
Point 2 (the effect, linked with "so"): so more fetch-execute cycles can be completed each second, and instructions are processed faster.
✓
Two linked points = 2 marks. "It makes the computer faster" alone gets 0, because it restates the question.
Example 3 — a 3-mark "describe" answer on the Computer Misuse Act
1
Question: describe the three offences under the Computer Misuse Act 1990.
2
Section 1: unauthorised access to computer material (1 mark).
3
Section 2: unauthorised access with intent to commit a further offence (1 mark). Section 3: unauthorised modification of programs or data on a computer (1 mark).
✓
Three separate offences, each described = 3 marks. Naming "hacking" three times would earn 1.
Now you try
Before you start the test, answer these quickly to warm up your method.
Answer the following:
Convert −20 to 8-bit two's complement.
Give the denary value of the floating-point number 01100 001 (5-bit mantissa, 3-bit exponent).
State one reason someone might launch a DOS attack.
Any one of: financial (e.g. blackmail or harming a competitor), political (protest), personal (revenge).
⚠️ Common mistakes — examiner feedback
Getting the sign of the exponent wrong. Shifting the mantissa right by n places to normalise makes the exponent +n. Shifting it left by n places makes the exponent −n.
Not normalising. A positive mantissa must start 01 and a negative one 10. Check before you write the answer.
Mixing up range and precision. More mantissa bits give more precision. More exponent bits give more range.
Vague security answers. "It's dangerous" earns nothing. Say exactly what is at risk and why — e.g. a tracking cookie builds a profile of the sites you visit, which can be sold without your knowledge.
Mixing up public and private keys. You encrypt with the recipient's public key. A digital signature is made with the sender's private key.
📝 Exam tip
Count the marks, then count your points. In the 2–4 mark "describe" and "explain" questions, most lost marks come from making one good point and then repeating it in different words. Before moving on, number your points in your head. If a question is worth 4 and you have made 2 distinct points, you have more to write.
Task Set B — The test (40 marks)
Task Set B — Computer Systems unit test · 40 marks
24 questions. Answer every question first, then press Check answers once at the end. Numeric answers are auto-checked; written answers are self-marked against the model answer.
Q1 · Binary integers (CS1) · 1 mark
State the largest positive integer that can be stored in 10 bits using unsigned binary.
Q2 · Two's complement (CS2) · 1 mark
Convert −45 to 8-bit two's complement.
Q3 · Two's complement (CS2) · 1 mark
The 8-bit two's complement number 10110110 is stored in memory. State its denary value.
Q4 · Two's complement range (CS2) · 1 mark
State the most negative number that can be stored in 12-bit two's complement.
Q5 · Two's complement range (CS2) · 2 marks
8-bit two's complement can store −128 but not +128. Explain why.
Model answer
Q6 · Floating point (CS3) · 2 marks
Represent 2.75 in normalised floating point using a 5-bit mantissa and a 3-bit exponent, both in two's complement. Write the mantissa, a space, then the exponent.
Q7 · Floating point (CS3) · 1 mark
A normalised floating-point number has mantissa 10100 and exponent 011 (both two's complement). State its denary value.
Q8 · Floating point (CS3) · 1 mark
A normalised floating-point number has mantissa 01110 and exponent 101 (both two's complement). State its denary value as a decimal.
Q9 · Range and precision (CS3) · 2 marks
A system stores real numbers in 32 bits: 24 bits for the mantissa and 8 bits for the exponent. It is changed to 20 bits for the mantissa and 12 bits for the exponent. Describe the effect on the precision and the range of the numbers that can be stored.
Model answer
Q10 · ASCII (CS4) · 1 mark
Extended ASCII uses 8 bits per character. State how many different characters it can represent.
Q11 · Unicode (CS4) · 1 mark
A website will be used by people writing in many different languages. Describe the advantage of storing its text in Unicode rather than extended ASCII.
Model answer
Q12 · Bitmap and vector graphics (CS5) · 2 marks
A company logo made of simple shapes must be printed on both a business card and a large billboard. Explain why a vector graphic is more suitable than a bitmap.
Model answer
Q13 · Fetch-execute cycle (CS7) · 3 marks
Describe the steps of the fetch-execute cycle that fetch the next instruction from memory.
Model answer
Q14 · Performance factors (CS8) · 1 mark
A computer's data bus is widened from 32 bits to 64 bits. Which statement describes the effect?
Q15 · Performance factors (CS8) · 2 marks
Explain how cache memory improves the performance of a computer system.
Model answer
Q16 · Performance factors (CS8) · 2 marks
A computer is upgraded from a 2-core processor to a 4-core processor. A pupil expects every program to run twice as fast. Explain why this may not happen.
Model answer
Q17 · Environmental impact (CS9) · 3 marks
Describe how each of the following intelligent systems can reduce environmental impact: (a) a heating system, (b) a traffic control system, (c) a car management system.
Model answer
Q18 · Computer Misuse Act (CS10) · 1 mark
An employee guesses a colleague's password and logs in to read their emails. Nothing is changed or copied. Which offence has been committed?
Q19 · Computer Misuse Act (CS10) · 2 marks
A pupil gets into the school's records system without permission and changes their own test marks. Name the main offence under the Computer Misuse Act 1990 and justify your answer.
Model answer
Q20 · Tracking cookies (CS11) · 2 marks
Explain the security risk of tracking cookies.
Model answer
Q21 · DOS attacks (CS11) · 4 marks
An online shop suffers a denial of service attack. Describe: (a) one symptom users would notice, (b) one cost to the shop, (c) one type of fault the attack could cause, and (d) one reason someone might carry out the attack.
Model answer
Q22 · Encryption (CS12) · 1 mark
Asha wants to send Ben a message that only Ben can read. Which key should Asha use to encrypt it?
Q23 · Digital signatures (CS12) · 2 marks
Describe how a digital signature is used to show that a message really came from the person who claims to have sent it.
Model answer
Q24 · Digital certificates (CS12) · 1 mark
State the purpose of a digital certificate.
Model answer
Task Set C — Revision planning
Task Set C — Revision planning
Use your own Task Set B results to plan what to revise next. No auto-check.
C1
List every question you did not get full marks on, and the lesson it comes from.
One possible answer
C2
For your two weakest questions, describe exactly what you will do to fix each one. "Revise it" is not enough.
One possible answer
C3
Is there a pattern in the marks you lost — one area of the course, or one type of question? What does that tell you?
One possible answer
📁 File this in OneNote under: Higher Computing Science → Computer Systems → CS14
📌 Teacher notes — Shift+T to hide
Origin: an original, site-native 40-mark test written from the Higher course specification (Computer Systems content statements 1.1–1.4) and matched to the methods taught in CS1–CS12. It is not a copy of the department EOTT1/EOTT2 papers, which could not be opened when this was built. Swap questions in from those papers if preferred, but keep IDs B1–B24 attached to their original questions and give any new question the next free ID (B25…).
Suggested timing: 5 min warm-up and "How this test works" · 55 min test under exam conditions · 10 min self-marking · 10 min Task Set C.
Mark allocation: 1.1 = 16 (Q1–Q12) · 1.2 = 8 (Q13–Q16) · 1.3 = 3 (Q17) · 1.4 = 13 (Q18–Q24). Auto-checked: Q1–Q4, Q6–Q8, Q10, Q14, Q18, Q22 (12 marks). Q6 is 2 marks: 1 for the mantissa, 1 for the exponent — the auto-check is all-or-nothing, so award 1 by hand if only one part is right.