Compare CPU cores, cache and clock speed
Explain how core count, cache size and clock speed can affect performance without treating one measure as decisive.
Exam scope and assessment notes
This sequence follows Cambridge IGCSE Computer Science 0984, 2026–2028 syllabus Version 4. It covers subject content sections 3.1–3.3 only. The separately published 2029–2031 syllabus is not mapped here. Practice is original, self-checked and does not award an official Cambridge grade. Full timed papers and human subject-teacher review remain outstanding. Cambridge states that 0984 has the same 2026–2028 subject content as 0478, with 9–1 grading. In June and November, Cambridge lists 0984 in Administrative zone 3 and for centres in Oman and the UAE. Confirm availability for your centre and exam series with Cambridge International. The separately published 2029–2031 syllabus changes to Python 3 only and removes pseudocode; this 2026–2028 route does not cover those changes.
Before you begin
- No programming language is required. Be comfortable with place value and multiplication; each lesson introduces the computer-science notation it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is cache used for?
What you will learn
- Explain what a CPU core does
- Explain why cache can reduce memory waiting
- Relate clock speed to cycles per second and discuss performance limits
Three features can influence speed
A core can execute instructions; more cores can allow more work to be processed at once when software and tasks can use them. Cache is fast memory close to the CPU that keeps frequently needed instructions or data, reducing some trips to slower RAM.
Apply and check the rule
Clock speed is the number of clock cycles each second. A higher clock can allow more cycles in the same time, but actual performance also depends on the instruction workload, core use, cache behaviour and other design factors. Compare systems in context rather than using one specification alone.
Pause and explain
Why can extra CPU cores help one task but not another?
Worked example
Two CPUs have the same clock speed, but one has more cores. Which is guaranteed to finish every task faster?
Show the worked solution
- More cores can process parallel work.
- Some tasks cannot use all cores effectively.
- No CPU is guaranteed to be faster for every workload from core count alone.
Answer Neither is guaranteed to finish every task faster; the result depends on workload, software and other CPU features.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A clock runs at 3 GHz. Approximately how many cycles occur each second?
Give me a hint
Giga means one billion.
Compare my reasoning
- 3 GHz means 3 billion cycles per second.
- Write 3×10⁹ cycles each second.
3,000,000,000 cycles per second
Look for these in your work
- GHz interpreted
- Per-second unit included
Explain how a larger cache might improve CPU performance.
Give me a hint
Consider what happens when data is needed repeatedly.
Compare my reasoning
- Frequently used data or instructions can be kept near the CPU.
- The CPU can access cache faster than RAM.
- This can reduce time waiting for RAM, though it does not improve every workload equally.
A larger cache may keep more needed data close to the CPU and reduce some slower RAM accesses.
Look for these in your work
- Locality stated
- Access speed linked
- Conditional effect stated
A buyer compares CPU A with 8 cores at 2.5 GHz and CPU B with 4 cores at 3.4 GHz. Explain why the specifications alone do not determine which is better for a student's work.
Give me a hint
Compare parallel work and per-core cycles with software and other factors.
Compare my reasoning
- CPU A may handle more parallel tasks if software uses its cores.
- CPU B offers a higher clock rate per core for tasks that benefit from it.
- Cache, architecture, software, power and workload also affect performance; test the intended applications.
A may suit well-parallelised work and B may suit work limited by one core's speed. Cache, architecture and the actual software matter, so the core and clock figures alone do not prove a universal winner.
Look for these in your work
- Both specifications interpreted
- Workload dependency
- No unsupported absolute claim
Common mistakes
- Claiming more cores always make a single task proportionally faster
- Treating cache as permanent secondary storage
What can you explain now?
What does clock speed measure?
Compare with the explanation
Clock cycles per second
Clock speed gives the number of cycles generated each second.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Name three CPU features in the syllabus that can affect performance.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.