Community resourceWorksheet

J277 1.1.2 CPU performance

Part 2 of 6 · J277 1.1 · Systems architecture

The three characteristics OCR J277 uses to explain CPU performance: clock speed, cache size and number of cores.

Students will:

  • explain clock speed, cache size and number of cores
  • build a cause-and-effect chain for each characteristic
  • compare processor specifications
  • justify a processor choice from several pieces of evidence
  • explain why more of one characteristic is not always a proportional gain

Inside: 6 explanation cells, 3 multiple-choice questions, 2 fill-in-the-blanks cells and 4 written answers. 39 marks, about 75 minutes.

Series: J277 1.1 · Systems architecture, part 2 of 6.

Shared by Coding PathwayVerified teacher

  • 15 cells
  • About 75 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026
  • Updated 9 Sept 2026

Preview

The whole resource, exactly as a class sees it. Answers and marking are held back.

Systems architecture 2: CPU performance

CPU performance is affected by three characteristics named in OCR J277: clock speed, cache size and number of cores. You need to understand each characteristic and explain the effects of changing them individually or in combination.

Processor tables can look complicated at first. You do not need to decide from every number at once. Learn one cause-and-effect chain for each characteristic, then combine them when a question gives you a scenario.

By the end of this worksheet, you should be able to:

  • explain clock speed, cache size and number of cores
  • build cause-and-effect explanations for each characteristic
  • compare processor specifications
  • apply performance knowledge to a scenario
  • recognise why “more” does not always produce a proportional improvement
  • justify a processor choice using several pieces of evidence
Multiple choice1 mark

Before you begin, which component performs arithmetic calculations and logical comparisons?

  • AControl unit
  • BArithmetic logic unit
  • CCache
  • DRegister

1. Clock speed

The CPU's clock produces regular electronic pulses that coordinate processing. Clock speed is the number of clock cycles per second and is measured in hertz. Modern processor speeds are often expressed in gigahertz (GHz), where 1 GHz represents one billion cycles per second.

A higher clock speed can allow the processor to carry out more fetch-execute cycles, and therefore process more instructions, in the same time.

Build the explanation as a chain:

higher clock speed → more cycles per second → potentially more instructions processed per second → improved performance

Do not write only “the clock is faster”. Name the characteristic as clock speed and explain the effect.

Fill in the blanks4 marks
label 1 measures the number of label 2. It is often measured in label 3. Increasing it can allow more label 4 to be processed in the same time.
  • cores
  • cycles per second
  • clock speed
  • instructions
  • gigahertz
  • cache size

2. Cache size

Cache is small, fast memory in or close to the CPU. It stores frequently or recently used data and instructions.

A larger cache can hold more of the items that the processor may need again. If the required item is found in cache, the CPU can access it more quickly than from RAM. This can reduce waiting and improve performance.

Build the chain:

larger cache → more frequently used data and instructions can be held close to the CPU → fewer or quicker accesses than repeatedly retrieving them from RAM → improved performance

The required characteristic is cache size, not just “cache” or “memory”.

Written answer3 marks

Explain how increasing cache size can improve CPU performance.

Build a three-step chain: what a larger cache can hold, how access compares with RAM, and the effect on CPU waiting or processing.

Students type their answer here.

3. Number of cores

A core is a processing unit within a CPU that can carry out its own fetch-execute cycle. A multi-core processor contains more than one core.

More cores can allow more instructions or tasks to be processed at the same time. This can improve multitasking and programs that divide their work into parts that can run in parallel.

Build the chain:

more cores → more instructions or tasks can be processed simultaneously → less time needed for suitable workloads → improved performance

The improvement depends on the software and task. If a program cannot divide its work between cores, additional cores may be unused. Twice as many cores does not guarantee twice the performance.

Multiple choice, several answers3 marks

Which three statements about processor cores are accurate? Select all that apply.

  • AEach core can carry out its own fetch-execute cycle
  • BDoubling the number of cores always makes every program exactly twice as fast
  • CMore cores can process more instructions or tasks simultaneously
  • DA core is a permanent storage device for user files
  • ESoftware must be able to divide suitable work between cores to gain the full benefit
Fill in the blanks6 marks
Increasing label 1 can increase the number of label 2 completed each second. Increasing label 3 can keep more label 4 data and instructions close to the CPU. Increasing the label 5 can allow suitable tasks to be processed label 6.
  • simultaneously
  • secondary storage
  • clock speed
  • number of cores
  • sequentially
  • frequently used
  • cycles
  • cache size

4. Compare factors together

OCR can ask about characteristics individually or in combination. Read every specification rather than deciding from one number.

ProcessorClock speedCache sizeCores
A3.8 GHz8 MB4
B3.2 GHz16 MB8

Processor A has the higher clock speed. Processor B has the larger cache and more cores. There is no single correct choice without knowing the task.

For a program that mainly uses one core, A's higher clock speed may be more useful. For several parallel tasks, B's additional cores may be more useful. B's larger cache may also reduce slower accesses to RAM.

A sound recommendation follows this structure:

choice → relevant specification → how it affects processing → benefit in the scenario

The model below keeps the three mechanisms separate. Follow each row from the changed characteristic to its possible effect, then check the condition at the right.

Three causal routes from CPU characteristics to performance Three rows show that higher clock speed provides more cycles per second, larger cache can reduce slower RAM access, and more cores can process work simultaneously when software can divide the work. Characteristic → mechanism → possible performance effect Higher clock speed more cycles each second potentially more instructions processed each second Not the only factor compare like-for-like CPUs Larger cache more nearby storage more frequently used items may be found without using RAM Less waiting when the needed item is cached More cores more processing units instructions or tasks may be processed at the same time Software-dependent work must be divisible A sound comparison uses the mechanism and the workload, not just the largest number.
Written answer6 marks

Using the table above, compare processors A and B. Explain one possible performance advantage of each.

For each processor, quote the relevant characteristic and explain how it could affect processing.

Students type their answer here.

Multiple choice, several answers4 marks

Which four statements would be sufficiently precise in an exam answer? Select all that apply.

  • AThe processor is better because it has more clock
  • BA higher clock speed allows more clock cycles to be completed per second
  • CA larger cache can hold more frequently used data and instructions
  • DMore cache always makes every program twice as fast
  • EMore cores can allow suitable tasks to be processed simultaneously
  • FAdditional cores may give little benefit if the software cannot use them
Written answer6 marks

A video-editing application can divide rendering work across several cores. Processor C has 4 cores, a clock speed of 4.0 GHz and 8 MB cache. Processor D has 8 cores, a clock speed of 3.5 GHz and 16 MB cache.

Recommend one processor for the video editor and justify your choice.

State the choice first. Use at least two relevant characteristics, explain how they affect performance and include one drawback or limitation. A well-supported choice matters more than simply choosing the processor with the largest numbers.

Students type their answer here.

Written answer6 marks

Challenge: test the “more is always better” claim. Evaluate the statement, “The processor with the largest numbers in its specification will always run every program fastest.”

Build a connected response. Explain all three OCR characteristics, how they can work in combination and why the workload or software matters, then reach a judgement.

Students type their answer here.

Closed-book review

Without looking back, write one cause-and-effect chain for each characteristic:

  • higher clock speed → ...
  • larger cache size → ...
  • greater number of cores → ...

Then add one sentence explaining why more cores may not improve a particular program. Check that you used each full characteristic name.