💻 Paper 1 · Topic 3: Computer Hardware
3.1b CPU Performance Factors
Edexcel 1CP2 · GCSE Computer Science · ~12 min read · 🔒 Pro
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What Affects CPU Performance?

Three main factors determine how fast a CPU can process instructions:

1. Clock Speed

Measured in GHz (gigahertz). Each clock pulse allows the CPU to perform one operation. A higher clock speed means more operations per second.
Example: a 4 GHz CPU performs 4 billion cycles per second.
Effect: higher clock speed = faster processing.

2. Number of Cores

A core is an independent processing unit within the CPU. A multi-core processor has multiple cores that can each handle different instructions simultaneously (parallel processing).
A dual-core processor has 2 cores, quad-core has 4, etc.
Effect: more cores = more tasks done simultaneously (good for multitasking and parallel programs).

3. Cache Size

Cache is a small, very fast memory inside the CPU. Frequently used data and instructions are stored in cache so they don't need to be fetched from (slower) RAM each time.
There are typically multiple cache levels: L1 (smallest, fastest), L2, L3 (largest, slowest of the three).
Effect: larger cache = fewer slow RAM accesses = faster processing.

Summary Table

FactorWhat it isEffect on performance
Clock speedGHz — cycles per secondHigher = faster FDE cycle
Number of coresIndependent processing unitsMore = better parallel processing
Cache sizeFast memory near CPU (L1, L2, L3)Larger = fewer slow RAM accesses

Diminishing Returns

Simply increasing one factor doesn't always give proportional gains. For example:

  • A program that isn't written for parallel processing won't benefit from more cores
  • Increasing clock speed too much causes overheating
  • Cache helps most when the same data/instructions are reused frequently
Exam tip: Edexcel 1CP2 questions commonly ask: "State and explain three factors that affect CPU performance." Make sure you explain the effect of each factor — don't just name them. For example: "More cores allow multiple instructions to be executed simultaneously, improving performance when running parallel tasks."
⚠️ Common Mistakes
  • Saying "RAM" instead of "cache" — they're different! Cache is inside/near the CPU; RAM is separate
  • Claiming more cores always means faster — single-threaded programs don't benefit
  • Confusing clock speed (GHz) with cache (MB)
  • Not explaining HOW the factor improves performance
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Worksheet — 3.1b CPU Performance Factors

8 Edexcel-style questions · instantly marked

Q1State three factors that affect the performance of a CPU.[3]
✅ Mark scheme
Clock speed [1]; Number of cores [1]; Cache size [1].
Q2Explain how increasing clock speed improves CPU performance.[2]
✅ Mark scheme
Clock speed determines how many cycles per second the CPU performs [1]; a higher clock speed means more FDE cycles per second, so more instructions are processed [1].
Q3What is a core in a CPU?[2]
✅ Mark scheme
A core is an independent processing unit within the CPU [1]; each core can execute its own set of instructions simultaneously [1].
Q4Explain how cache memory improves CPU performance.[2]
✅ Mark scheme
Cache stores frequently used instructions/data [1]; the CPU can access this faster than RAM, reducing wait time [1].
Q5A CPU runs at 3 GHz. How many cycles does it perform per second?[1]
✅ Mark scheme
3 billion (3,000,000,000) cycles per second [1].
Q6Why might doubling the number of cores not double the speed of all programs?[2]
✅ Mark scheme
Some programs are written for single-threaded execution and cannot run tasks in parallel [1]; these programs cannot take advantage of extra cores [1].
Q7State the order of cache levels from fastest to slowest.[1]
✅ Mark scheme
L1 (fastest) → L2 → L3 (slowest of cache levels, but still much faster than RAM) [1].
Q8Explain one disadvantage of increasing clock speed too much.[2]
✅ Mark scheme
Increasing clock speed generates more heat [1]; this can cause overheating and require more cooling, potentially damaging the CPU [1].
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Mini Test — CPU Performance

Timed exam-style test.

← 3.1a CPU ArchitectureTopic 3Next: 3.1c Memory →
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